Dennis T Ray

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Scholarly Contributions

Books

• Shotwell, M. A., & Ray, D. T. (2016). Genetics: Lab Manual (Third Edition). Kendall Hunt Publishing Company.
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  Mark A. Shotwell and Dennis T. Ray. 2016. Genetics: Lab Manual (Third Edition), Kendall Hunt Publishing Company, 168 pages.Lab Exercises 1-8 were completely redone: Mitosis and Meiosis; Probability and Mendelian Genetics; Dominance Relationships, Gene Interaction, and Epistasis; Pedigree Analysis; Crossing Over and Linkage Mapping; Chromosomes and Karyotypes; Quantitative Genetics; and Population Genetics. The last three exercises were omitted and two new lab exercises included Bacterial Transformation; and PCR Amplification of DNA.Originally, this was written for our specific courses, but with the changes we made this year it can now be used by other universities, and this semester (Spring 2017) is used at 4 schools.
• Ray, D. T., & Shotwell, M. A. (2013). Genetics: Laboratory Manual: Second Edition Revised Printing. Kendal Hunt.

Chapters

• Abdel-Haleem, H., Luo, Z., & Ray, D. T. (2019). Chapter 6: Breeding and Genetic Improvement of Guayule, an Alternative Rubber Crop. In Advances in Plant Breeding Strategies, Industrial and Food Crops(pp 151-178). Springer Nature Switzerland AG. doi:https://doi.org/10.1007/978-3-030-23265-8_6
• Coffelt, T. A., Ray, D. T., & Dierig, D. A. (2015). 100 Years of Breeding Guayule. In Industrial Crops: Breeding for Bioenergy and Bioproducts/Springer Series, Industrial Crops Breeding for BioEneregy and Bioproducts(pp 351-367). Industrial Crops Breeding for BioEneregy and Bioproducts, Handbook of Plant Breeding, Vol. 9: Springer Science.
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  Terry Coffelt was the corresponding author.

Journals/Publications

• Shawn, T. L., Neff, M. W., & Ray, D. T. (2020). The 2020 ASHS Annual Conference - rapid transition to a fully virtual meeting. Chronica Horticulturae, 60(4), 14-15.
• Abdel-Haleem, H., Foster, M. A., Ray, D. T., & Coffelt, T. A. (2018). Phenotypic variations, heritability and correlations in dry biomass, rubber and resin production among guayule improved germplasm lines. Industrial Crops and Products, 112, 691-697. doi:https://doi.org/10.1016/j.indcrop.2017.12.072
• Ottman, M. J., & Ray, D. T. (2018). Plant spacing and row width effect on productivity of sweet sorghum. Agronomy Journal, 110(3), 1008-1016. doi:10.2134/agronj2017.07.0389
• Cruz, V. V., Lynch, A. L., Ray, D. T., Niaura, W. S., Purdy, P. H., & Dierig, D. A. (2017). Analysis of mode of reproduction of guayule (Parthenium argentatum A. Gray) using flow cytometry and identification of polyhaploids for breeding. Industrial Crops and Products, 107, 618-623. doi:http://dx.doi.org/10.1016/j.indcrop.2017.07.004
• Pearson, B. J., Moore, K. A., & Ray, D. T. (2017). Introduction: Developing Soft Skills in Tomorrow's Leaders. HortTechnology, 37(5), 579. doi:10.21273/HORTTECH0376-17
• Ray, D. T., Winzerling, J. J., & Staten, M. E. (2017). Career Skills: Our Process and Where we are Today. HortTechnology, 27(5), 586-590. doi:10.21273/HORTTECH03671-17
• Teetor, V. H., Schmalzel, C., & Ray, D. T. (2017). Growing sweet sorghum (Sorghum bicolor [L.] Moench) in clumps potentially reduces lodging in the arid-southwestern United States. Industrial Crops and Products, 107, 458-462. doi:http://dx.doi.org/10.1016/j.indcrop.2017.05.064
• Liu, J., Bronson, K. F., Thorp, K. R., Mon, J., Badaruddin, M., Mccloskey, W. B., Ray, D. T., Chu, Q., & Wang, G. (2014). Lesquerella seed and Oil Yield Response to Split-Applied N Fertilizer. Industrial Crops and Products, 60, 273-279.
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  This is work from the Lesquerella grant that I am the PI, and Sam Wang was the Corresponding Author.
• Dierig, D. A., Dahlquist, G. H., Coffelt, T. A., Ray, D. T., Isbell, T. A., & Wang, G. (2013). Registration of WCL-LO4-Gail Lesquerella with Improved Harvest Index. Journal of Plant Registrations, 7, 339-341.
• Dierig, D. A., Dahlquist, G. H., Coffelt, T. A., Ray, D. T., Isbell, T. A., & Wang, G. (2013). Registration of WCL-LO4-gail lesquerella with improved harvest index. Journal of Plant Registrations, 7(3), 339-341.
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  Abstract: WCL-LO4-Gail lesquerella (Physaria fendleri L.) germplasm line (Reg. No. GP-34, PI 666045) was publicly released jointly by the USDA-ARS and the University of Arizona, in 2012 as part of the new crops breeding program. The germplasm was developed by mass selection originating from lesquerella germplasm WCL-LO3. The germplasm has an average oil content of 29% and 44% lesquerolic acid. It has a harvest index of 16.5, a plant biomass of 157 g, and a seed yield of 23.5 g plant-1. The unique characteristic of this germplasm is its demonstrated improved harvest index. The release of WCL-LO4-Gail will beneft public and private breeders with new germplasm for variety development. It will also benefit growers and producers with the highest yielding available germplasm for production. © Crop Science Society of America.
• Duclos, D. V., Ray, D. T., & Taylor, A. G. (2013). Investigating seed dormancy in switchgrass (Panicum virgatum L.): understandding the physiology and mechanisms of coat-imposed seed dormancy. Industrial Crops and Products, 45, 377-387.
• Duclos, D. V., Ray, D. T., Johnson, D. J., & Taylor, A. G. (2013). Investigating seed dormancy in switchgrass (Panicum virgatum L.): Understanding the physiology and mechanisms of coat-imposed seed dormancy. Industrial Crops and Products, 45, 377-387.
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  Abstract: Switchgrass (Panicum virgatum L.), a perennial warm-season grass established by seed has been recommended by the US Department of Energy as a model herbaceous biofuel crop. Neoteric seeds may be dormant resulting in delayed and sporadic germination and emergence, jeopardizing establishment of a good plant stand. Switchgrass dormancy may be alleviated by mechanical or chemical scarification, stratification, and after-ripening, suggesting physical and/or physiological dormancy. The underlying mechanisms and physiology of dormancy in these seeds; however, are not well understood. This work investigates the physiology of switchgrass seed dormancy; first by identifying the contribution of the different switchgrass structures (glumes, lemma, palea, pericarp/testa, endosperm) on regulating germination, and then by testing specific mechanisms of coat-imposed dormancy. We sequentially removed structures of freshly harvested seeds of two upland (Cave-in-Rock, Trailblazer) and two lowland (Alamo, Kanlow) cultivars. The main structure inhibiting germination was the pericarp/testa, with the lemma and palea (bracts) having a secondary effect that differed by genotype. Seeds with glumes and bracts removed, and pericarp/testa cut with endosperm either attached or removed just above the embryo, resulted in high germination percentages and rate, indicating no morphological dormancy, and no effect of the endosperm on germination. The lemma, palea, and pericarp/testa were neither a barrier for water uptake nor contained inhibitory compounds. By adjusting the oxygen concentration of the environment and the physical integrity of the covering structures, we found the enclosing structures acted as barriers to oxygen. Puncturing the pericarp/testa of seeds with glumes and bracts removed, enhanced germination at 1, 10, 21 or 100% oxygen. Combined results showed that the structural integrity of the pericarp/testa (primary) and lemma/palea (secondary) influenced germination, suggesting an important mechanical effect of these layers as barriers for radicle protrusion. Therefore, a combination of seed-coat mechanisms regulates germination in switchgrass seeds. © 2013 Elsevier B.V.
• Dierig, D., Dahlquist, G., Coffelt, T., Ray, D., Isbell, T., & Wang, G. (2012). Registration of WCL-L04-Gail lesquerella with improved harvest index.
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  Publically jointly released germplasm line by USDA-ARS and the University of Arizona.
• Pessarakli, M., Kopec, D., Harivandi, A., & Ray, D. (2012). Growth Responses and Nitrogen Uptake by Saltgrass (Distichlis spicata L.), a Halophytic Plant Species, Under Salt Stress, Using the N15 Technique. International Journal of Agronomy.
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  Article ID 896971, 9 pages, doi:10.1155/2012/896971(on-line publication).
• Dierig, D. A., Wang, G. S., McCloskey, W. B., Thorp, K. R., Isbell, T. A., Ray, D. T., & Foster, M. A. (2011). Lesquerella: New crop development and commercialization in the U.S.. Industrial Crops and Products, 34(2), 1381-1385.
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  doi:10.1016/j.indcrop.2010.12.023
• Dierig, D. A., Wang, G., McCloskey, W. B., Thorp, K. R., Isbell, T. A., Ray, D. T., & Foster, M. A. (2011). Lesquerella: New crop development and commercialization in the U.S.. Industrial Crops and Products, 34(2), 1381-1385.
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  Abstract: While Lesquerella fendleri Gray (Wats.) is not yet a commercial crop, its history serves as a model for new crop development. The most important characteristic is the absence of any significant biological barriers to commercialization. Other potential crops may have valuable, high-demand products but possess traits difficult to overcome such as seed shattering or poor yield capacity. Lesquerella has a distinctive plant architecture that is conducive to seed productivity under a variety of conditions, and the trait could be further exploited. The plant also has high amounts of within-species and interspecific genetic diversity allowing breeding improvements in traits including oil quantity and quality. The unique seed oil is predominately composed of a hydroxy fatty acid, lesquerolic acid (C20:1OH), that is similar to ricinoleic acid (C18:1OH) found in castor oil. Improvements in agronomics will help increase seed yields, water use efficiency, while reducing crop production costs. New tools offered by remote sensing will help plant breeders and growers assess crop development. Defining herbicides and obtaining registrations for use in lesquerella appears to be the biggest obstacle for commercialization of this crop. The improvements in agronomics, breeding, genetics, and the expansion of new markets started in the 1980's, and has made lesquerella a viable potential crop that could utilize thousands of hectares in arid climates of the world provided research continues. © 2010.
• Dierig, D., Wang, G., McCloskey, W., Thorp, K., Isbell, T., Ray, D., Foster, M., & Crafts-Brandner, S. (2011). Lesquerella: New Crop Development and Commercialization in the U. S.. Industrial Crops and Products, 34, 1381-1385.
• Pessarakli, M., Kopec, D. M., & Ray, D. T. (2011). Growth responses of various saltgrass (Distichlis spicata) clones under salt stress conditions. Journal of Food, Agriculture and Environment, 9(3-4), 660-664.
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  Abstract: Continuous desertification of arable lands mandates use of low quality/saline water for irrigation, especially in regions experiencing water shortage. Using low quality/saline water for irrigation imposes more stress on plants which are already under stress in these regions. Thus, a logical solution could be finding a salt tolerant plant species to survive/sustain under such salinity stress conditions. Since the native plants are already growing under such conditions and are adapted to the stress, they are the most suitable candidates for use under these harsh arid saline soil conditions. If the salt stress tolerant species/genotypes of these native plants are identified, there would be a substantial savings in inputs in using them under these stressful conditions. Our studies on various native grasses indicated that saltgrass has a great potential to be used under harsh environmental desert conditions and combat desertification. The objectives of this study were to find the most salinity tolerant types of various saltgrass clones and to recommend them as the potential species for use under arid regions and areas with saline soils or saline water resources for sustainable agriculture and combating desertification. Various saltgrass clones were studied in a greenhouse to evaluate their growth responses under salinity stress conditions. Grasses were grown vegetatively in a hydroponics system under 4 saline treatments [EC = 6 (control), 20, 34, and 48 dSm -1 salinity stress] with 3 replications of each salinity treatment in a randomized complete block (RCB) design experiment. During this period, shoots were clipped bi-weekly for dry matter (DM) weight determination. At the last harvest, roots were also harvested and DM weights determined. Grass quality was weekly evaluated. Although growth responses reduced at the high salinity levels, all the grasses showed a high degree of salinity tolerance. However, there was a wide range of variations observed in salinity tolerance among the clones. The superior salinity tolerant clones were identified which could be recommended for sustainable production under arid regions and combating desertification.
• Pessarakli, M., Kopec, D., & Ray, D. (2011). Growth responses of various saltgrass (Distichlis spicata) clones under salt stress. Journal of Food, Agriculture & Environment, 9, 660-664.
• Teetor, V. H., Duclos, D. V., Wittenberg, E. T., Young, K. M., Chawhuaymak, J., Riley, M. R., & Ray, D. T. (2011). Effects of planting date on sugar and ethanol yield of sweet sorghum grown in Arizona. Industrial Crops and Products, 34(2), 1293-1300.
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  Abstract: Sweet sorghum (Sorghum bicolor (L.) Moench) is an annual crop currently being investigated for biofuel production in the arid southwest United States (U.S.). Sweet sorghum is an ideal candidate because it can be grown under reduced inputs (water, fertilizer) and responds more efficiently to stresses than traditional crops. Many varieties have been bred for high sugar, syrup, and forage production, but much biodiversity still remains to be utilized.Studies performed in 2006 and 2007 found that high biomass and percent juice extracted were the best predictors of potential ethanol yield per area. This investigation was undertaken to determine what effects planting dates have on overall sugar and predicted ethanol yields.Four varieties (Dale, M81E, Theis, and Topper) were planted in April, May, June, and July of 2008. They were harvested at physiological maturity, with dates ranging from August 26 to December 2. Biomass, juice weight, and Brix of the juice were recorded in the field. Samples were analyzed in the laboratory by High Performance Liquid Chromatography (HPLC) for fructose, glucose, and sucrose.Theoretical ethanol yields were calculated based on biomass, juice weight, and percent sugar. These were compared to actual yields obtained from laboratory-scale fermentations of the harvested juice, which ranged from 7.4% to 11.2% (58.1-88.6gL-1). Since our predictive model uses the maximum conversion rate of sugar to ethanol and this was not reached in the lab, the predicted yields were always higher than the actual yields. However, the model can be a useful tool for estimating ethanol yield per area.Total sugars and predicted ethanol production were influenced by planting date, but the degree of the effects depended on the cultivar planted. Overall a May planting date at this location is preferable due to consistently higher values for the yield components analyzed, and Theis is not recommended due to its high susceptibility to heat. Sweet sorghum juice has been successfully fermented into ethanol, which indicates this crop may be able to play a transitory role in the emerging biofuel market. © 2010 Elsevier B.V.
• Teetor, V., Duclos, D., Wittenberg, E., Young, K., Chawhuaymak, J., Riley, M., & Ray, D. (2011). Effects of Planting Date on Sugar and Ethanol Yield of Sweet Sorghum Grown in Arizona. Industrial Crops and Products, 34, 1293-1300.
• Coffelt, T. A., & Ray, D. T. (2010). Cutting height effects on guayule latex, rubber, and resin yields. Industrial Crops and Products, 32(3), 264-268.
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  Abstract: Guayule (Parthenium argentatum Gray) is a perennial shrub native to the Chihuahuan Desert. While guayule traditionally has been cultivated for rubber, more recently it is being cultivated for its hypoallergenic latex. Other uses including termite resistant wood products and as an energy source have also been identified. Major advances have been made since 1970 in the development of improved guayule germplasm. However, the effects of harvesting practices such as cutting height and frequency on latex concentration and yield of newly developed germplasm have not been reported. These results are needed in order to develop production schemes for successful commercialization of guayule. The objectives of this study were to determine the yield and concentration of latex, rubber, and resin of five guayule lines harvested at two cutting heights over 3 years and five harvesting schedules. Harvesting at 100% of plant height gave higher yields than harvesting at 50% of plant height independent of the harvest schedule. Harvesting at 100% after 4 years of growth gave the highest yields, but more research is needed to determine if harvesting on a 2-year schedule may be better for harvesting equipment and extraction equipment. AZ-2 and AZ101 were the largest plants, while N9-3 and 11591 were smaller with AZ-1 intermediate. As indicated in previous studies, the environment plays a large role in determining biomass, latex, rubber, and resin yields in guayule. In the future, optimum harvesting schemes at 100% of plant height may need to be developed for each line and environment. © 2010.
• Ray, D. T., Foster, M. A., Coffelt, T. A., & McMahan, C. (2010). Guayule: Culture, breeding and rubber production. Industrial Crops and Uses, 384-410.
• Zerai, D. B., Glenn, E. P., Chatervedi, R., Zhongjin, L. u., Mamood, A. N., Nelson, S. G., & Ray, D. T. (2010). Potential for the improvement of Salicornia bigelovii through selective breeding. Ecological Engineering, 36(5), 730-739.
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  Abstract: Salicornia bigelovii Torr. is an annual salt marsh plant that produces seed oils, protein meal, fresh salad greens and forage on seawater irrigation. We compared S. bigelovii lines produced in two breeding programs with wild germplasm in greenhouse trials on brackish water (10 ppt NaCl) irrigation. S. bigelovii is an out-crossing species that is also capable of selfing, and the breeding programs showed it is possible to use both hybridization and pedigree breeding to improve the germplasm. Lines selected in a breeding program carried out in Eritrea, Africa, had smaller plant size and lower biomass yields than the starting germplasm, due to the need to compress the growth cycle within the cool months of the year in that hot climate, but seed yields and harvest index were improved. Lines produced from wild germplasm by mass selection and hybridization in Tucson, Arizona had higher biomass yield than starting germplasm. We conclude that S. bigelovii has sufficient genetic diversity among wild accessions and cultivars to support a crop improvement program. © 2010 Elsevier B.V. All rights reserved.
• Coffelt, T. A., Nakayama, F. S., Ray, D. T., Cornish, K., & McMahan, C. M. (2009). Post-harvest storage effects on guayule latex, rubber, and resin contents and yields. Industrial Crops and Products, 29(2-3), 326-335.
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  Abstract: Guayule is a new crop being commercialized for hypoallergenic latex production. Because natural processes that occur in the plant following harvest, notably dehydration, result in rapid loss of latex and immediate processing of guayule shrub for latex on a commercial scale is not feasible, storage conditions that maintain latex concentration and yield need to be established. The objective of this study was to determine the effects of different storage conditions on the extractable latex, total rubber, resin, and guayulin A and B contents, and extractable latex, total rubber, and resin yields in harvested guayule shrub. The experiment was established using plants transplanted into the field at the University of Arizona Maricopa Agricultural Center, Maricopa, AZ, USA, on 22 March 2001. A randomized complete block design with four replications was used. Two germplasm lines (11591 and AZ-2) were used for this experiment. Twenty plants of each line were harvested six times (November 2002, March 2003, July 2003, November 2003, March 2004, and July 2004) from each field plot. Two plants of each line were randomly assigned to each of 10 storage treatment combinations reflecting wet, dry, or wet alternated with dry conditions prior to chipping for latex extraction. Extractable latex content, total rubber content, resin content, and guayulin A and B contents were determined after storage and compared with freshly harvested shrub. Plant biomass, latex yield, rubber yield, and resin yield were also determined and compared with fresh harvested shrub. AZ-2 was significantly lower in latex, rubber, and guayulin A content than 11591, and significantly higher in biomass, latex yield, rubber yield, resin content, resin yield, and guayulin B content. The results from this study show that moist storage of harvested shrub prior to dry chipping allows a higher yield of latex. Storing the shrub under moist conditions may allow more flexible harvesting and processing schedules, by limiting post-harvest latex losses and increasing the time interval between harvesting and processing.
• Coffelt, T. A., Nakayama, F. S., Ray, D. T., Cornish, K., McMahan, C. M., & Williams, C. F. (2009). Plant population, planting date, and germplasm effects on guayule latex, rubber, and resin yields. Industrial Crops and Products, 29(1), 255-260.
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  Abstract: Guayule (Parthenium argentatum Gray) is a perennial shrub native to the Chihuahuan Desert. While guayule traditionally has been cultivated for rubber, more recently it is being cultivated for its hypoallergenic latex. Other uses including termite resistant wood products and an energy source have also been identified. However, the effects of various agronomic practices, such as planting and harvesting dates, plant spacing, cutting height and frequency, irrigation frequency, and herbicide application, on latex concentration and yield of newly developed germplasm have not been reported. The objectives of this study were to determine the yield and concentration of latex, rubber, and resin of four guayule lines planted at two populations and two planting dates. Four guayule lines (AZ-1, AZ-3, AZ-5, and 11591) were transplanted at two dates (28 November 2000 and 7 June 2001) and two plant populations (27,000 and 54,000 plants ha-1). Treatments were replicated four times. Each treatment plot was subdivided into six subplots for harvesting at 6-month intervals beginning 1 year after transplanting. Results showed that transplanting date did not affect plant size or latex concentration or yield consistently. Instead, it appeared that the time of harvest (fall vs. spring) was more important. The sixth (last harvest) in the fall planting date and the fifth harvest date in the spring planting date were the optimum for plant biomass and latex, rubber, and resin concentrations and yields. The lines AZ-1 and AZ-3 were larger, whereas AZ-5 had higher latex and rubber concentrations than the control, 11591. The greater plant population (54,000 plants ha-1) had higher biomass, rubber, and resin yields than the lower population (27,000 plants ha-1) at the early harvest dates, but not at the later harvest dates (5 and 6). More studies must to be conducted to determine the optimum plant population and transplanting date for other newly developed guayule germplasm lines.
• Cornish, K., Williams, J. L., Kirk, M., Teetor, V. H., & Ray, D. T. (2009). Evaluation & control of potential sensitizing & irritating chemical components in natural rubber latex extracted from the industrial crop guayule. Industrial Biotechnology, 5(4), 245-252.
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  Abstract: Guayule natural rubber is commercially available as an emulsion base-material for latex medical devices, including medical gloves and catheters. These products do not cause reactions in Type I latex allergic humans. In addition to natural rubber, guayule produces terpene resin comprised of hundreds of isoprenoid compounds. One group, the guayulins, is a major terpenoid component of guayule resin; the most abundant, guayulin A, comprises 1-10% of the resin fraction. An earlier study concluded that guayulins are contact sensitizers in guinea pigs, although they appeared much less sensitizing in humans. The possibility that residual guayulins may be present in the guayule natural rubber emulsions at a sensitizing level is of concern. We quantified the levels of guayulin and resin in purified natural rubber emulsions, using HPLC. Guayulin concentrations fell rapidly, due to hydrolysis at high pH, reaching a steady state after 4-6 weeks. The localized lymph node assay (LLNA) in mice was used to assess sensitization potential of guayule resin and guayulin A. Guinea pig patch tests were used to assess irritation and sensitization. Mouse ear swelling and rabbit repeated patch testing were used to assess irritation. No sensitization or irritation by guayulin A was observed. Guayule resin was irritating at concentrations of 10% and above, but no sensitization occurred. The LLNA and dermal test data indicate that it is extremely unlikely that guayule latex products will cause sensitization or irritation due to the presence of trace guayulins or other resin compounds co-extracted with the guayule natural rubber emulsion. © 2009, Mary Ann Liebert, Inc.
• Teetor, V. H., Ray, D. T., & Schloman Jr., W. W. (2009). Evaluating chemical indices of guayule rubber content: Guayulins A and B. Industrial Crops and Products, 29(2-3), 590-598.
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  Abstract: Guayule (Parthenium argentatum Gray) is now a commercial crop for the production of high-quality, hypoallergenic natural rubber latex. Because guayule is relatively resistant to both insect and disease pests, its cultivation requires little chemical input. It has been postulated that guayule's chemical defense system is based on terpene derivatives such as guayulins A and B. The goals of this research were to: (1) describe the distribution of guayulins A and B throughout the plant, (2) determine whether guayulins can be used as a predictor of rubber content/yield (is guayulin content related to rubber content), and (3) determine whether the guayulin content/distribution has been changed through plant breeding. Two plants each of three different lines (11591, AZ-1, and AZ-3) and two ages (1 and 2 years old) were harvested at the soil line in the fall of 2002 and spring of 2003. Plants were separated into eight parts: brown leaves, green leaves, stem tips, stems less than 5 mm in diameter, stems between 5 and 10 mm, stems greater than 10 mm, green stems, and flower parts. Samples were analyzed for guayulins A and B and rubber content. Guayulins A and B and rubber were found in all plant parts, but were most prevalent in stems larger than 10 mm in diameter, and were significantly correlated with each other in these stems. Guayulin A was found in greater concentrations than guayulin B. There were no significant differences between plant ages for rubber, or guayulin content at the time of harvest, or guayulins for harvest season. Rubber percent was higher in spring, which agrees with numerous other investigations. Guayulin A in the stems is correlated with the total rubber in the plant, suggesting it as a potential selection tool. However, rubber in the same plant parts has a higher correlation with total plant rubber and remains a better and easier selection criterion than guayulin A. The extent to which guayulin contents differed between older, relatively unimproved lines and newer improved lines was evaluated. Variety 11591 had a higher concentration of guayulin A than guayulin B, so that the ratio of A to B was much higher than in the two improved lines (AZ-1 and AZ-3). It appears that the ratio of guayulin A to guayulin B has been changed in the two newer selections, but it is unclear whether this will affect pest resistance. © 2008 Elsevier B.V. All rights reserved.
• Xu, Y., Marron, M. T., Seddon, E., McLaughlin, S. P., Ray, D. T., Whitesell, L., & Gunatilaka, A. L. (2009). 2,3-Dihydrowithaferin A-3β-O-sulfate, a new potential prodrug of withaferin A from aeroponically grown Withania somnifera. Bioorganic and Medicinal Chemistry, 17(6), 2210-2214.
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  PMID: 19056281;Abstract: Preparations of the roots of the medicinal plant Withania somnifera (L.) Dunal commonly called ashwagandha have been used for millennia in the Ayurvedic medical tradition of India as a general tonic to relieve stress and enhance health, especially in the elderly. In modern times, ashwagandha has been shown to possess intriguing antiangiogenic and anticancer activity, largely attributable to the presence of the steroidal lactone withaferin A as the major constituent. When cultured using the aeroponic technique, however, this plant was found to produce a new natural product, 2,3-dihydrowithaferin A-3β-O-sulfate (1), as the predominant constituent of methanolic extracts prepared from aerial tissues. The characteristic bioactivities exhibited by 1 including inhibition of cancer cell proliferation/survival, disruption of cytoskeletal organization and induction of the cellular heat-shock response paralleled those displayed by withaferin A (2). The delayed onset of action and reduced potency of 1 in cell culture along with previous observations demonstrating the requirement of the 2(3)-double bond in withanolides for bioactivity suggested that 1 might be converted to 2 in cell culture media and this was confirmed by HPLC analysis. The abundant yield of 1 from aeroponically cultivated plants, its good aqueous solubility and spontaneous conversion to 2 under cell culture conditions, suggest that 1 could prove useful as a readily formulated prodrug of withaferin A that merits further evaluation in animal models. © 2008 Elsevier Ltd. All rights reserved.
• Henrique, M., Veatch-Blohm, M. E., & Ray, D. T. (2007). Quality of guayule seeds separated by physical attributes. Industrial Crops and Products, 25(1), 55-62.
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  Abstract: Guayule (Parthenium argentatum Gray) is being developed as a new commercial crop to be grown in arid and semiarid regions. Guayule stands are presently established using transplants; however, establishment by direct-seeding would reduce costs and make production more economical. A major difficulty in field establishment by direct-seeding is the variation in the quality of guayule seeds. Guayule seeds vary greatly in color, size, and weight, which are the attributes believed to be associated with the observed germination differences among and within seed lots. To determine the importance of these attributes, guayule seeds from different seed lots were separated by size (diameter) and color, each separation class was weighed and then seed quality determined by germination percentage and rate. X-ray analysis was used to distinguish filled from unfilled seeds, and this was related to the germination results. In six guayule breeding lines (N565, 11591, AZ-2, AZ-3, AZ-4, and AZ-5), the highest quality seeds were darker (opaque-black and gray), small to medium in diameter (1.4-1.6 mm), and were heavier (a greater proportion of filled seeds). Color appeared to be a more efficient separator for seed quality than seed size; however, separation by size may be acceptable on a large scale and still provide higher quality and more uniform seed lots. © 2006 Elsevier B.V. All rights reserved.
• Veatch-Blohm, M., Ray, D. T., & Gehrels, A. (2007). Night temperature, rubber production, and carbon exchange in guayule. Industrial Crops and Products, 25(1), 34-43.
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  Abstract: Guayule (Parthenium argentatum Gray), a native of the Chihuahuan desert, produces the majority of its rubber during the winter months. Increased rubber production is thought to be induced by cold night temperatures, but the factors involved in rubber induction are not completely understood. The purpose of this study was to answer three questions about rubber production in the winter: (1) how do immature plants (
• Jorge, M. H., Veatch-Blohm, M. E., Ray, D. T., & Foster, M. A. (2006). Guayule seed germination under different conditioning treatments. Industrial Crops and Products, 24(1), 60-65.
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  Abstract: Guayule (Parthenium argentatum Gray), a latex producing shrub from northern Mexico and southwestern Texas, has been considered a viable alternative commercial crop for arid lands throughout the world. Stand establishment by direct seeding has been ineffectual because of problems with seed germination. Seed dormancy has been ascribed as one of the main reasons for low germination. Special seed treatments, such as physical and chemical conditioning, have been devised to overcome embryo and seed coat dormancy, thereby improving germination and emergence. However, the treatments described in the literature have not been as effective as expected, and many of them are costly and time consuming. The objective of this study was to determine the effects of nine preconditioning treatments on the percentage and rate of germination and emergence, and seedling fresh weight. Three-year-old seed of lines AZ-101, AZ-3, and N9-3 were analyzed with X-ray to determine the seed lot quality. The results showed differences in quality (defined as seeds containing embryos and endosperm) among the three lines; however, no differences were found for percentage and rate of germination and emergence, and seedling fresh weight among the nine treatments. These results suggest that in older seed lots seed quality is of greater importance in determining germination and emergence than conditioning treatments. © 2006 Elsevier B.V. All rights reserved.
• McMahan, C. M., Cornish, K., Coffelt, T. A., Nakayama, F. S., III, R. M., Brichta, J. L., & Ray, D. T. (2006). Post-harvest storage effects on guayule latex quality from agronomic trials. Industrial Crops and Products, 24(3), 321-328.
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  Abstract: Current guayule commercialization efforts are based upon the production of hypoallergenic latex. The objective of this study was to determine how latex yield and quality are affected by post-harvest plant storage in order to provide flexibility in the harvesting, chipping, and processing steps for guayule latex. The experiments were conducted on two lines (11591 and AZ-2) at the University of Arizona Maricopa Agricultural Center, from March 2001, through December 2004. Weight-average molecular weight of guayule latex increased as the plants aged from 1.7 to 2.7 years. Guayule latex quality was affected by shrub storage conditions, and addition of moisture extended the storage time for guayule shrub without negatively impacting molecular weight for both varieties. However, under extreme conditions, for example, high temperatures and extended dry storage times, polymer molecular weight reduction of up to 30% occurred. © 2006 Elsevier B.V. All rights reserved.
• Schloman Jr., W. W., Teetor, V. H., & Ray, D. T. (2006). Protein levels affect the cure efficiency and allergenic potential of polyisoprene latices. Rubber Chemistry and Technology, 79(4).
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  Abstract: Commercial MR latex has a higher total protein content than guayule (GR) latex. Some MR proteins are allergens bound to the rubber particle surface. Washing NR latex with a non-ionic surfactant displaced these particle-bound proteins and reduced allergens by more than 95%. The cost of such deproteination was reduced vulcanization efficiency, as determined by crosslink density. The extent of vulcanization correlated well with both total protein and allergen levels. Compared with films prepared from untreated NR latex, films from both surfactant-treated NR latex and GR latex had lower states of cure. Where particle-bound proteins were still present, as they are in GR latex, crosslink development could be completed by heat aging. In contrast, crosslink development in the film from surfactant-treated NR was complete after dipping and drying. The resulting films yielded high levels of extractable protein allergens.
• Veatch-Blohm, M. E., Ray, D. T., & McCloskey, W. B. (2006). Water-stress-induced changes in resin and rubber concentration and distribution in greenhouse-grown guayule. Agronomy Journal, 98(3), 766-773.
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  Abstract: Guayule (Parthenium argentatum A. Gray) is naturally subject to periods of water stress in its native habitat. It has been shown that, under cultivation, rubber yields increase with increasing irrigation, but rubber concentration per plant decreases. The effect of irrigation on resin concentration is unclear. The purpose of this study was to understand how resin concentration is affected by water stress, and why water stress increases rubber concentration. Greenhouse-grown guayule plants were subjected to water stress in four experiments, each of 3 mo duration. Two experiments were conducted in the summer, the active growth period, and two experiments were conducted in the winter. The water-stressed plants were irrigated when the average soil water potential reached either -0.6 MPa (first summer experiment) or -0.3 MPa (all subsequent experiments). Water-stress effects were monitored by measuring growth, C exchange, biomass, and resin and rubber production. Water-stressed plants had lower C exchange, growth, and leaf-to-stem ratio than well-watered plants. Resin concentration did not respond consistently to water stress. Rubber concentration was generally higher in the water-stressed plants than in the well-watered plants as a result of decreased leaf biomass in both the summer (33 vs. 45 g kg-1) and winter (36 vs. 52 g kg-1) and decreased stem diameter in the summer (8.1 vs. 11.0 mm). Rubber is deposited mainly in the bark; therefore, reduced leaf biomass and stem diameter contribute to higher rubber concentration in the water-stressed plants by increasing the relative amount of bark. © American Society of Agronomy.
• Coffelt, T. A., Ray, D. T., Nakayama, F. S., & Dierig, D. A. (2005). Genotypic and environmental effects on guayule (Parthenium argentatum) latex and growth. Industrial Crops and Products, 22(1), 95-99.
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  Abstract: Guayule (Parthenium argentatum Gray) is the best potential source of hypoallergenic latex to replace latex products from the Hevea (Hevea brasiliensis) plant that cause Type I allergies. However, information is not available on environmental effects on latex content and growth of newly released germplasm lines. This knowledge is needed to enhance guayule breeding efforts. The objectives of this study were to evaluate the genotype, environment, and genotype × environment effects on latex content and plant growth of guayule. Four lines were planted in the field at Maricopa, Arizona, USA on 6 April 1995 and 6 March 1996 and at Marana, Arizona, USA on 11 April 1995 and 12 June 1996. Plant height and width measurements were made in the spring of 1997 and latex content and biomass determined in the spring of 1997 and 1998. The main factors that included location, line, and plant age were significant and the interactions not significant for all traits measured. Environment accounted for over 50% of the variability observed in all traits, followed by plant age (16%) and line (10%). These results point to the tremendous impact that environment has on guayule plant growth, biomass, and latex content. We could not determine from these tests whether temperature, soil type, moisture, fertility, or a combination of these or other environmental factors were responsible for this response. Some of the non-significant interactions may have been significant if a larger or wider germplasm base could have been evaluated. Additional studies are needed to determine the environmental factor(s) responsible for the large environmental response we observed.
• Cornish, K., McMahan, C. M., Pearson, C. H., Ray, D. T., & Shintani, D. K. (2005). Biotechnological development of domestic rubber producing crops. Rubber World, 233(2), 40-44.
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  Abstract: The biotechnological development of crops used to produce domestic rubber, to achieve significant gains in latex and rubber yield, was described. Molecular approaches appear to be the most suitable approach for making substantial improvements in rubber yield and quality in alternative rubber-producing plant species suitable for cultivation in temperate, rather than tropical, regions. P.argentatum lines developed from conventional plant breeding programs are already being produced on commercial scale. However, a combination of biochemistry-based approaches and genomics and proteomics methods using model systems, could generate the fundamental understanding needed to fully exploit molecular methods and generate significantly improved new lines.
• Henrique, M., & Ray, D. T. (2005). Germination characterization of guayule seed by morphology, mass and, X-ray analysis. Industrial Crops and Products, 22(1), 59-63.
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  Abstract: Guayule is a shrub native to northcentral Mexico and southwestern Texas and is economically important because it produces non-allergenic latex. Seed quality is an important factor in guayule stand establishment and found to vary greatly among seed lots. We hypothesized that this variation was due to the presence or absence of internal structures (e.g., embryo and endosperm) within the seed. The objective of this study was to characterize seed lots as to seed size, color and weight, and then analyze the relationship between X-ray image pattern of each and germination percentage. X-ray was used to discriminate between filled, partially filled, and unfilled seed, and thus, the relationship between internal structures and seed viability. Two seed sizes, 1.80 and 1.57 mm, of breeding line 11591 were separated into four color grades (bright-black, opaque-black, gray and yellow). Seeds were weighed and each category X-rayed. Germination tests were then performed. Results showed that yellow and bright-black seeds tended to be lighter in weight than gray and opaque-black seeds. It was possible to separate color grades by weight. In addition, germination percentage was higher with heavier seed than with lighter seed. After separation by X-ray and germination analysis, results showed that filled seed had a higher germination percentage than partially filled and unfilled seeds. Data from the X-ray image patterns and germination tests strongly suggest that the presence of internal structures plays a major role in germination of guayule seed. We conclude that X-ray could be used in seed lots to improve the quality of guayule seed germination by separating the filled seeds from the unfilled or partially filled seeds. © 2004 Elsevier B.V. All rights reserved.
• Ray, D. T., Coffelt, T. A., & Dierig, D. A. (2005). Breeding guayule for commercial production. Industrial Crops and Products, 22(1), 15-25.
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  Abstract: Breeding a new domestic crop, such as guayule, is not appreciably different from enhancement and breeding of conventional crops. In both instances, plant breeders take the available germplasm and search for genetic variability in the desired traits. The major differences are that in new crops plant breeders are often working with an unfamiliar species that is not yet fully domesticated and the available germplasm is often limited. The main objective of the guayule breeding program is to facilitate successful commercialization by developing higher yielding cultivars. Improvement has been accomplished, with newer lines yielding up to 250% more rubber than lines developed in the 1940s and 1950s. This is surprising because the genetic base from which improvements have been made appears to be very narrow, and because guayule reproduces predominately by apomixis (asexual reproduction by seed). Improvements through breeding are dependent upon genetic diversity within the available germplasm, and being able to identify different genotypes. The available germplasm exhibits extreme variability both within and between lines for morphological traits such as height, width, and biomass; chemical constituents such as rubber, resin, and latex contents; and genetic and chromosomal markers. The measured variation is due partly to the facultative (asexual reproduction and sexuality coexisting) nature of apomixis in guayule, which periodically releases genetic variation among progeny. A great amount of this measured variation is due to environment, and selections, to take advantage of genetic differences, must be made within the first 2 years of growth. There have been relatively few individuals involved in guayule breeding. Thus, with limited resources and time, most of the improvements have been made through single-plant selections from within populations. Although this method has the potential for only modest long-term gains, improvements occur relatively quickly. Indirect measures have been developed to increase breeding efficiency. For instance, most selections are made for plant height, width and biomass because they are highly correlated with rubber yield. As guayule approaches commercialization, breeding will become a priority and other breeding schemes will be tested and utilized such as: mass selection; recurrent selection among sexually reproducing diploids, followed by chromosome doubling; family selection; crossing high yielding apomictic plants; and crossing high yielding apomictic plants to sexual diploid plants to release new genetic combinations. Crown Copyright © 2004 Published by Elsevier B.V. All rights reserved.
• Veatch, M. E., Ray, D. T., Mau, C. J., & Cornish, K. (2005). Growth, rubber, and resin evaluation of two-year-old transgenic guayule. Industrial Crops and Products, 22(1), 65-74.
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  Abstract: Guayule (Parthenium argentatum Gray) is a desert shrub that is a source of hypoallergenic, high-quality latex and rubber. Improvements in rubber content and yield have been made through conventional selection techniques. Further improvements are being attempted by transforming guayule with one of three genes encoding various allylic diphosphate synthases in the rubber biosynthesis pathway. The objective of this study was to evaluate the effect of these transgenes on growth, rubber and resin production, in field-grown guayule. Tissue culture-generated transgenic plants of the lines AZ 101, AZ-2 and N6-5 were planted in two field plots in 2001 and 2002. In both plots, plant height and width were measured monthly. Branches from each plant were sampled every four months starting at one year of growth. Resin and rubber were quantified by gravimetric analysis after being sequentially extracted with acetone (resin) and cyclohexane (rubber). The 2001 plot was harvested at the end of two years of growth. Transformation had no significant effect on growth of AZ-2 and N6-5 in the two years of the 2001 planting and the first year of the 2002 planting. In the 2001 planting, transformation appeared to have a drastic effect on the height and width of transformed AZ 101 compared with its empty vector control; however, the field in this study was not randomized and lacked non-transformed controls. In the 2002 planting, which was randomized and contained both positive and negative controls, the AZ 101 transformants were significantly larger than the empty vector AZ 101 control, but were not significantly different from the non-transformed controls. In the 2001 planting, resin concentration increased throughout the year up to January 2003, but decreased by the time of harvest in March 2003. Rubber concentration, on the other hand, was high in May 2002, but decreased throughout the summer, before steadily increasing during the winter months. © 2004 Elsevier B.V. All rights reserved.
• Dierig, D. A., Tomasi, P. M., Salywon, A. M., & Ray, D. T. (2004). Improvement in hydroxy fatty acid seed oil content and other traits from interspecific hybrids of three Lesquerella species: Lesquerella fendleri, L. pallida, and L. lindheimeri. Euphytica, 139(3), 199-206.
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  Abstract: Interspecific hybridization offers potential to improve the hydroxy fatty acid (HFA) content of lesquerella. Lesquerella fendleri is currently being developed for cultivation as a potential new industrial oilseed crop because of its seed productivity. However, it has lower HFA content compared to L. pallida and L. lindheimeri. The objectives of this research were to improve the HFA oil content of L. fenderi through interspecific hybridization and to characterize hybrids and successive generations for seed oil fatty acid profile, fertility, seed set and other morphological traits. In this work, three species were successfully hybridized, self-pollinated, and backcrossed. Ovule culture was used in some cases to produce progeny where interspecific hybrids did not produce viable embryos. The traits measured were petal length, ovules per silique, seeds per silique, and weight of 1000 seed. Patterns of leaf trichomes were used to distinguish between parents and hybrids. Seed per silique indicated that autofertility occurred in L. pallida but not in the other two species. HFA oil content of L. fendleri seed were 50.5% compared to 80 and 84% for L. pallida and L. lindheimeri, respectively. The HFA oil content of the hybrids ranged from 57 to 70% in A2 and A3 generations, and the range of values depended on the parents used in the crosses. These measurements will help predict the value of different interspecific crosses for breeding. Segregation for various yield related traits should allow selection for favorable improvements in the HFA trait and in seed yield. © 2004 Kluwer Academic Publishers.
• Keys, R. N., & Ray, D. T. (2002). Characterization of apomictic potential in guayule (Parthenium argentatum) in vivo and in vitro. Journal of the American Society for Horticultural Science, 127(3), 404-408.
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  Abstract: Guayule (Parthenium argentatum Gray), a latex-producing perennial desert shrub and potential industrial crop for semiarid regions, exhibits reproductive modes ranging from sexual, self-sterile diploids to predominantly apomictic, self-compatible polyploids. The objectives of this study were to develop and evaluate a rapid, simple technique for characterizing apomictic potential (percentage of ovules that produce apomictic embryos) in guayule breeding lines. Initial in vivo experiments were based on an auxin test that permitted quantification of apomictic frequency in grasses. In our trials, floral application of NAA or IBA resulted in embryo production similar to that of open-pollinated controls, but 2,4-D inhibited embryo production. Breeding lines could be separated based on embryo production using an in vivo auxin test; however, accuracy of the results was questionable because 1) pollen release and insect activity within isolation bags prevented distinguishing between sexual and apomictic embryos, and 2) high temperatures and large humidity fluctuations could have affected results. Thus, in vitro flower culture was investigated using liquid medium, because it would provide better control of these factors. Flowers developed normally in vitro, except that pollen was not released from the anthers; therefore, any embryos produced in vitro were considered to be apomictic. Embryo production was similar on both Nitsch and Nitsch and Woody Plant Media. Addition of growth regulators inhibited embryo production. Embryo production was tested on Nitsch and Nitsch medium without growth regulators for seven breeding lines. Based on statistical analyses, four classes of apomictic potential were identified, ranging from none (sexual) to high. Chemical names used: 2,4-dichlorophenoxy acetic acid (2,4-D); indole-3-butyric acid (IBA); α-naphthaleneacetic acid (NAA).
• Dierig, D. A., Ray, D. T., Coffelt, T. A., Nakayama, F. S., Leake, G. S., & Lorenz, G. (2001). Heritability of height, width, resin, rubber, and latex in guayule (Parthenium argentatum). Industrial Crops and Products, 13(3), 229-238.
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  Abstract: Plant breeding in guayule, a rubber and latex producing plant, has not been as effective as predicted or desired. A surprisingly large amount of variability has been reported in this apomictic crop for traits such as plant height, width, resin, rubber, and latex contents. This study was designed to calculate the proportion of the total measured variability due to the environment and the proportion due to genetic influences within and between three-released germplasm lines. Plant heights were measured at 1, 2 and 3-years-of-age; plant width, and latex contents at 2 and 3-years-of-age; and resin and rubber content at 2-years-of-age. Broad-sense-heritabilities were estimated for each trait and year by dividing the genotypic by the total variance. To estimate the genetic component of the measured variance for each trait, the environment effects (variance from clonally propagated plants) were subtracted from the total variance (variance from open-pollinated (OP) seed propagated plants). In general, the variances of the means for the measured traits were lower in the clonally propagated plants compared with the apomictic OP seed propagated plants. The heritability estimates calculated for each trait differed from year to year. For instance, heritability for plant height was estimated in line AZ-2 to be 0.84 at 1 year of age; 0.47 at 2 years of age; and 0.0 at 3 years of age. These values imply that a large portion of the observed variation in this line is attributed to genetic effects in the first 2 years of growth. As the plant grows over several seasons, the environment effects compound, masking the genetic effects, making effective selection choices more difficult. Heritability for latex content for the same line was estimated to be 0.97 for the second year and 0.55 for the third year. Selections for the measured traits in this study appear to be most effective during the first and second years of growth, with effectiveness diminishing during the third year. Most selections previous to this study were performed between 3 and 5 years of growth, thus suggesting one reason for the lack of significant progress in most breeding programs. © 2001 Elsevier Science B.V. All rights reserved.
• Dierig, D. A., Tomasi, P. M., & Ray, D. T. (2001). Inheritance of male sterility in Lesquerella fendleri. Journal of the American Society for Horticultural Science, 126(6), 738-743.
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  Abstract: Lesquerella fendleri (Gray) Wats. (lesquerella, Brassicaceae), native to the southwestern United States, is a potentially useful industrial oilseed crop. The seed oil contains hydroxy fatty acids, similar to castor (Ricinus communis L.) seed oil. The unique properties of the oil, along with coproducts, allow additional applications that would not compete with castor oil. Plants with vestigial anthers (male-sterile) were discovered in a greenhouse-grown, nonselected population in 1993. The inheritance of the trait was investigated through four crop seasons. Crosses were made among male-sterile and male-fertile plants from an open pollinated population, thus, they were heterozygous for many traits. Statistical analysis indicated that male sterility is expressed as a result of two nonlinked nuclear genes with epistatic relations and different cytoplasms, which cause partial or total fertility restoration. These ratios fit a 13:3 epistatic ratio, indicating that male sterility is controlled by homozygous recessive alleles at one locus in combination with at least one dominant allele at the second locus, i.e., ms1ms1 Ms2_. Some cross results were skewed in favor of fertile phenotypes presumably due to cytoplasmic effects causing partial fertility restoration. Male-sterile lines could be used for hybrid development and this information will be helpful in implementing a strategy for hybrid development. Hybrid plants and higher yields will enhance the potential for commercialization of this new alternative crop.
• Stumpf, D. K., Ray, D. T., & W.W., J. S. (2001). Identification of a contact allergen in guayule latex and formulated guayule latex products [3]. JAOCS, Journal of the American Oil Chemists' Society, 78(2), 217-218.
• Ray, D. T., Dierig, D. A., Thompson, A. E., & Coffelt, T. A. (1999). Registration of six guayule germplasms with high yielding ability. Crop Science, 39(1), 300-.
• Brahim, K., Ray, D. T., & Dierig, D. A. (1998). Growth and yield characteristics of Lesquerella fendleri as a function of plant density. Industrial Crops and Products, 9(1), 63-71.
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  Abstract: There is little information available regarding the response of Lesquerella fendleri to planting density. The effects of plant density on growth, yield, and yield components of L. fendleri were studied in central Arizona at plant populations of 250000, 500000, 750000, 1000000, and un-thinned controls of 1658000 plants/ha in 1992-1993 and 1500000 plants/ha in 1993-1994. In the 1992-1993 tests, increasing density resulted in a significant decrease in plant width and number of branches, while causing an increase in taproot length in populations up to 750000 plants/ha. There were no effects on seed size; however, density significantly reduced the number of seeds/silique for the 750000 and 1658000 plants/ha treatments. Seed yield/plant and harvest index/plant were significantly reduced with increasing density, but yield/ha increased with density up to 1000000 plants/ha. At 1658000 plants/ha, shattering was excessive and resulted in loss of seeds. The greatest seed yields/ha were obtained at 750000 plants/ha and 1000000 plants/ha densities. The oil content did not vary significantly from 500000 to 1658000 plants/ha, but treatments in this range produced seeds with significantly higher oil content than the 250000 plants/ha treatment. Differences in oil yield/ha reflected differences in seed yield/ha. The 1993-1994 harvest did not show significant differences for seed and oil yields among density treatments. Higher temperatures in 1993-1994 were believed to increase the oil content and seed yield in the higher plant densities. Plant densities of 750000 and 1000000 plants/ha are recommended for lesquerella growing areas comparable to central Arizona. At these densities, maximum seed yields should be obtained even with annual temperature fluctuations. Also, maximum plant heights were obtained at these densities, minimizing seed loses during combine harvest.
• Brahim, K., Stumpf, D. K., Ray, D. T., & Dierig, D. A. (1996). Lesquerella fendleri seed oil content and composition: Harvest date and plant population effects. Industrial Crops and Products, 5(3), 245-252.
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  Abstract: Yield losses of Lesquerella fendeleri L. seeds, caused by shattering and seed oil content reduction by excessive desiccation could be minimized by the appropriate choice of harvest dates. However, no information is available on harvest dates to maximize economic returns at any planting density. This research was undertaken to study the effects of harvest dates and plant populations on oil yield and composition in L. fendleri. Mechanically seeded field plots of L. fendleri were thinned at 103 days after sowing (DAS) to density treatments of 250,000, 500,000, 750,000, 1,000,000, and an nonthinned control of 1,500,000 plants/ha. These plants were grown in 1993-94 at The University of Arizona. Maricopa Agricultural Center in central Arizona, and were harvested at 203, 229, 243, and 264 DAS. Eight fatty acids, which make up 87-96% of mature seed oil, were investigated. These included palmitic (C16:0), palmitoleic (C16:1), stearic (C18:0), oleic (C18:1), linoleic (C18:2), linolenic (C18:3), lesquerolic (C20:1-OH), and auricolic (C20:2-OH) fatty acids. Generally, seed at the earliest harvest of 203 DAS had lower concentrations of palmitoleic, stearic, oleic, lesquerolic, and auricolic acids, and lower total oil content than those harvested at 229, 243, and 264 DAS. Also at 203 DAS, the 750,000 plants/ha treatment produced the highest fatty acid content yield, although both this oil and that from the 1,000,000 plants/ha treatment lacked auricolic acid. During this period, the major contributing fatty acids to oil content were oleic, linoleic, linolenic, and lesquerolic. Harvest at 229 DAS resulted in an increase in oil content for all treatments except the 750,000 plants/ha. Lesquerolic acid was the dominant oil for the nonthinned control. At 243 DAS, higher oil contents were observed in the 250,000, 750,000, and 1,000,000 plants/ha densities, with lesquerolic acid again the dominant fatty acid. At final harvest (264 DAS), lesquerolic acid content was virtually the same among the density treatments. No significant differences for seed yield, fatty acid composition or content were found among plant populations. The seed yield averaged over all population densities was 1344 kg/ha with a fatty acid content of 21.9%, giving an oil yield 267 kg/ha (calculated as total fatty acid content).
• Ray, D. T., & McCreight, J. D. (1996). Yellow-tip: A cytoplasmically inherited trait in melon (Cucumis melo L.). Journal of Heredity, 87(3), 245-247.
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  Abstract: A new chlorophyll-deficient mutant is the first cytoplasmically inherited trait described in melon. This mutant is characterized by yellow apices, with the leaves and stems progressively turning green in color as the branches mature. A protocol is proposed for naming and symbolizing cytoplasmic traits in melon. This mutation is named yellow-tip and is symbolized cyt-Yt. As a chlorophyll-deficient mutation, it is potentially useful in genetic, physiological, and biochemical studies.
• Ray, D. T., Orum, T. V., Bigelow, D. M., & Alcorn, S. M. (1995). Selection of diploid and screening of polyploid guayule lines for Verticillium tolerance. Industrial Crops and Products, 4(4), 303-310.
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  Abstract: Guayule (Parthenium argentatum Gray) produces a high quality hypoallergenic latex, that is of interest for use in the medical industry. In order to meet the anticipated demand, guayule will need to be planted in mild climatic zones over a wide geographic area, and often following cotton (Gossypium sp.) or other crops susceptible to the root-invading fungus Verticillium dahliae Kleb. Since guayule has been shown previously to be susceptible to V. dahliae, the goals of this work were: (1) to develop a diploid guayule line that is tolerant to V. dahliae through mass selection, and (2) to evaluate improved guayule lines for Verticillium tolerance. To achieve the first goal, a diploid guayule population was subjected to three cycles of selection, with only the plants with the greatest tolerance and the highest rubber yields used in the subsequent cycles of selection. Second, fifteen improved polyploid and three diploid lines were evaluated for tolerance to V. dahliae under greenhouse conditions. Cuttings were found to be more tolerant than seedlings, and tolerance increased with age of the plant at the time of inoculation. The Verticillium screened diploids expressed greater tolerance than an unscreened diploid population in both greenhouse and field trials. Among the 18 improved lines, 13 of which had not been previously evaluated, a Verticillium-screened diploid line (418-6) had the highest tolerance ranking, but was not significantly better than four unscreened polyploid lines. Continued evaluation of improved lines will help growers in making informed decisions about which lines to plant for their specific locations. The Verticillium-tolerant diploid germplasm material developed in this study is available to plant breeding programs. © 1995.
• Ray, D. T., Dierig, D. A., Thompson, A. E., & Diallo, M. M. (1993). Parent-offspring relationships in apomictic guayule. Journal of the American Oil Chemists' Society, 70(12), 1235-1237.
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  Abstract: The genetic base of guayule (Parthenium argentatum Gray) germ plasm that is available is narrow; yet, significant variability has been described within this germ plasm. This variability is surprising because guayule reproduces by facultative apomixis (asexual reproduction by seed), but evidence suggests that progress through selection is feasible. It has been hypothesized that this variation has arisen through periodic sexual reproduction; however, this has not been quantified. This study was designed to describe and compare eight components of yield and the expression of two isozyme systems in twenty parent plants and half-sib, open-pollinated families from each parent. Extensive variation for all characters was found among both the parents and the progeny, with fresh and dry weights being highly correlated to rubber yield. Parent-offspring regressions were not significantly different from zero. This implies low heritabilities for the major components of yield in guayule, and we believe that family selection, rather than single-plant selection, may generate higher-yielding and more genetically uniform lines at an escalated rate than single-plant selection. Periodic sexuality resulting in genetic variation was estimated by differences in isozyme expression within the half-sib families. Fifteen of the twenty progeny families were polymorphic for either esterase or peroxidase or both isozymes. This amount of sexuality is significant, and guayule must be considered an open-pollinated crop. We conclude from this study that we should rethink our breeding procedures to include controlled pollination and family selection. © 1993 American Oil Chemists' Society.
• Endrizzi, J. E., & Ray, D. T. (1992). Mapping of the cl₁, R₁, yg₁, and Dw loci in the long arm of chromosome 16 of cotton. Journal of Heredity, 83(1), 1-5.
• Gathman, A. C., Ray, D. T., & Livingston, M. (1992). Comparison of three stability measures in guayule. Industrial Crops and Products, 1(1), 67-74.
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  Abstract: Guayule (Parthenium argentatum Gray), a desert shrub native to the Chihuahuan desert of North America, is being domesticated as a potential rubber source. Two Uniform Regional Guayule Variety Trials were conducted in eleven locations using a total of twelve entries. Data from each of these trials were used to compute stability coefficients using the methods of Finlay and Wilkinson (1963), Eberhart and Russell (1966) and Zhang and Geng (1986). Results and interpretations of these methods were compared. Zhang and Geng's method was the most useful because it allowed comparison of entries grown in the two different yield trials. Using this method, the following conclusions were reached: Arizona breeding line AZ101 was significantly less stable than average in biomass and resin yield, '11605' was less stable than average for percent rubber, and 'Cal-6' and 'Cal-7' were less stable than average for rubber yield. Six entries ('N565', 'N576', '11591', '11605', '11619' and '12229') were significantly more stable than average for biomass yield, resin yield and rubber yield. Germplasm line N396 was also more stable than average for resin yield and percent resin. AZ101 was more stable than average for rubber percentage and rubber yield. Over all entries, there was a negative correlation between stability and yields of resin and rubber. © 1992.
• Ray, D. T., Coates, W., Livingston, M., & Garrot Jr., D. J. (1992). Mechanical pollarding as a means to increase rubber yields in guayule (Parthenium argentatum, Asteraceae). Industrial Crops and Products, 1(1), 11-15.
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  Abstract: Guayule (Parthenium argentatum Gray, Asteraceae) is a potential domestic source of natural rubber, but is presently not competitive economically with imported Hevea rubber. Guayule can become competitive by either increasing rubber yield or reducing the costs of cultural practices, or both. Pollarding, harvesting the branches by cutting leaving the root-crown to regrow new branches, can potentially increase both rubber yields and reduce the costs of stand establishment. The objective of this study was to determine the efficiency of mechanical-pollarding, and to determine if there were increased rubber yields one year after pollarding. A mechanical clipper was used to pollard shrub (accession N396), planted at the standard density of 36.650 plants ha. 17 and 29 months after stand establishment. Mechanical pollarding at 17 months left 19% of the branches unclipped on both a fresh and dry weight basis, representing 16% of the potential resin and rubber yield. After regrowth for one year (29 months), pollarded plants had increased fresh weight, dry weight and resin yield over non-pollarded plants of 25, 24 and 15%, respectively. However, rubber yield increased by only 3%, due mainly to the low rubber content in the regrowth. After a single pollarding (17 months) 98% of the plants survived and regenerated new growth. Plants pollarded two consecutive years (17 and 29 months) had only a 66% survival rate. The low rubber yield in the regrowth after one year, and the reduced survival rate of plants pollarded two consecutive years, suggests that a clipping interval of two years may be optimal for line N396. © 1992.
• Dierig, D. A., Thompson, A. E., & Ray, D. T. (1991). Effects of field storage on guayule rubber quantity and quality. Rubber Chemistry and Technology, 64(2), 211-.
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  Abstract: Successful commercialization of guayule (Parthenium argentatum Gray) depends on breeding and genetics to select and develop new high-yielding cultivars with good rubber quantity and quality. Many factors affect the physical properties of natural rubber (NR). The present study was undertaken to determine the effect of postharvest field storage of whole guayule plants on the quantity and quality of NR under Arizona conditions. Several different USDA lines, along with an interspecific hybrid, were included to study varietal differences. Plants in this study were grown under two irrigation regimes to test the effect of wet and dry growth conditions on NR.
• Endrizzi, J. E., & Ray, D. T. (1991). Linkage analysis of open bud (ob₂) and yellow petal (Y₁) in cotton. Genome, 34(3), 461-463.
• Endrizzi, J. E., & Ray, D. T. (1991). Monosomic and monotelodisomic analysis of 34 mutant loci in cotton. Journal of Heredity, 82(1), 53-57.
• Garrot Jr., D. J., Kilby, M. W., Stedman, S. W., Fangmeier, D. D., Ottman, M. J., Harper, J. M., Husman, S. H., & Ray, D. T. (1990). Irrigation scheduling using the crop water stress index in Arizona. ASAE Publication, 281-286.
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  Abstract: Field studies were conducted on five crops in Arizona to determine relationships between crop yield and the crop water stress index (CWSI). Small plots and/or commercial fields of long and short staple cotton, wheat, pecans, and watermelon were irrigated at preselected CWSI values representing low to high crop water stress levels. When using optimum CWSI irrigation scheduling values, a lower CWSI irrigation threshold should be used based on the time expected to elapse between the last CWSI reading and the actual irrigation event.
• Mamood, A. N., Ray, D. T., & Waller, G. D. (1990). Seed set in Guayule (Parthenium argentatum, asteraceae) in relation to insect pollination. Economic Botany, 44(4), 440-444.
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  Abstract: Guayule (Tarthenium argentatum, Asteraceae) is one of two major plant species grown for natural rubber. Studies were conducted to determine the effect of honey bee (Apis mellifera) pollination and season on seed set and total seed yield/ha. The experiments involved four pollination treatments: plants caged with bees; plants caged without bees; plants open pollinated (uncovered); and plants individually covered. Seeds were harvested monthly July-September 1984, and May-September 1985. Plots with bees produced at least 150% more seeds than plots without bees, and there were no qualitative differences in the seed weights among treatments. Highest seed yield was in May and September. Results indicate that (1) insect pollination in guayule increases seed yield and (2) fewer seeds are produced in the warmest months. © 1990 The New York Botanical Garden.
• Dierig, D. A., Ray, D. T., & Thompson, A. E. (1989). Variation of agronomic characters among and between guayule lines. Euphytica, 44(3), 265-271.
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  Abstract: A selected group of 42 guayule (Parthenium argentatum Gray) lines were evaluated on the basis of various morphological characteristics and compared to a total population of 234 lines. The objective of this study was to determine the amount of variation that existed both within and among guayule lines over a 2-year period. The parental lines all reproduced apomictically, and as expected, many lines exhibited a high degree of uniformity for every measured character. However, many other lines were extremely variable for varying numbers of characters. This appears to be due to varying degrees and combinations of apomeiosis, thus establishing a long-term source of genetic variation. The high amount of variability existing among and within these guayule lines indicates that significant progress by selection for both rubber percentage and yield is feasible. © 1989 Kluwer Academic Publishers.
• Dierig, D. A., Thompson, A. E., & Ray, D. T. (1989). Relationship of morphological variables to rubber production in guayule. Euphytica, 44(3), 259-264.
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  Abstract: The objective of this study was to find measurable characters to aid the plant breeder in predicting both rubber percentage and rubber yield of guayule (Parthenium argentatum Gray). A field of 234 guayule breeding lines was harvested by clipping in February 1986. Forty-two of these lines were selected for further evaluation on the basis of superior regrowth, rubber content and yield. These 42 lines were reharvested in February 1987. Nineteen variables were evaluated including percent rubber and resin, rubber and resin yield (g/plant), plant height (cm), width (cm), and volume (m3), fresh and dry weight (kg/plant), percent dry weight, stem number, mean stem diameter (cm), total and mean stem circumference (cm), total and mean stem area (cm2), total stem circumference/total stem area (cm-1), and regeneration at two dates. Dry weight (kg/plant) had the best correlation to rubber yield (r=0.85), and plant volume best predicted dry weight (r=0.83). These variables did not correlate as highly with percent rubber. The best statistical regression model for percent rubber included four variables, fresh and dry weight, percent dry weight, and plant volume. This model accounted for 51% of the variation. In comparison, the best regression of rubber yield had an R2=0.85 for plant height and width, volume, and dry weight. © 1989 Kluwer Academic Publishers.
• Gathman, A. C., & Ray, D. T. (1987). Meiotic analysis of 14 Cuphea species and two interspecific hybrids. Journal of Heredity, 78(5), 315-318.
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  Abstract: Melotic anlaysis of 14 species in the genus Cuphea confirmed haploid chromosome numbers from 6 to 22. All accessions within a species were found to have the same number of chromosomes with the exception of C. leptopoda accession 264, which had n = 8, while the other three accessions were n = 10. The probability of chlasma formation between a pair of chromosome arms was calculated for each accession and values ranged from 0.565 to 0.905. An Interspecific hybrid between two diplold Cuphea species was formed and the melotic pairing data used to establish a protocol for estimating genomic affinity in Cuphea. Melotic analysis of another Interspecific hybrid between the autotetra-plold, C. caesarlata, and its diplold progenitor, C. llavea, showed that the genomes have differentiated very little and that diplodization in C. caesarlata must have occurred quite rapidly. © 1987, American Genetic Association.
• Schioman Jr., W. W., Garrot Jr., D. J., & Ray, D. T. (1986). Water stress and seasonal effects on rubber quality in irrigated guayule. Journal of Agricultural and Food Chemistry, 34(4), 683-685.
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  Abstract: Guayule (line N396) was harvested monthly from January through July, 1984, from irrigated plots grown in Tucson, AZ. Irrigations were scheduled according to the crop water stress index (CWSI) to maintain three irrigation regimes. Plots were irrigated when their respective CWSI values reached or exceeded 0.3 (wet), 0.6 (medium), and 0.9 (dry). Individual plants from four replicated plots of each regime were analyzed for rubber molecular weight by gel permeation chromatography. The molecular weight (M̄w) values for all three irrigation regimes increased from January through March during the plants' winter quiescent period. Molecular weight decreased between March and April for all regimes when active growth resumed. By May, M̄w had increased above March values. Between irrigation regimes, significant differences in M̄w were observed only in January and June, with the dry plots yielding the highest molecular weight in both instances. © 1986 American Chemical Society.
• Schloman Jr., W. W., Garrot Jr., D. J., Ray, D. T., & Bennett, D. J. (1986). Seasonal effects on guayule resin composition. Journal of Agricultural and Food Chemistry, 34(2), 177-179.
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  Abstract: Rubber and resin levels in guayule line N396 were monitored on a whole-shrub basis from January through July 1984. This sample interval included the period of cold-weather stress associated with rubber formation and the period of renewed vegetative growth. Monthly levels were also determined for selected resin components. Fatty acid triglycerides were most abundant (>8000 ppm) in January, with lower levels (2300-4400 ppm) in succeeding months. Triterpenoid levels showed relatively little variation (1700-2500 ppm for argentatin A). Sesquiterpene esters were most abundant in March (3600 ppm for guayulin A) and July (2900 ppm) and least abundant in April and May (
• Fangmeier, D. D., Samani, Z., Garrot Jr., D., & Ray, D. T. (1985). WATER EFFECTS ON GUAYULE RUBBER PRODUCTION.. Transactions of the American Society of Agricultural Engineers, 28(6), 1947-1950.
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  Abstract: Guayule Parthenium argentatum Gray was transplanted in April and October 1980 near Litchfield Park, west of Phoenix, AZ. Four irrigation application depths were applied to plots in a randomized block design. Shrubs were harvested in June 1982, winter 1982-83, and January 1984. Dry matter produced, rubber content, and rubber yield were determined. Dry matter production increased with increasing water. Rubber content decreased with increasing water. Rubber yield showed a slight increase with increasing water. Estimated production costs show guayule is not economical to produce at current rubber prices. For the growing conditions at the site, 500 mm of irrigation water application annually would be most economical but more costly than guayule grown under better soil conditions.
• Fangmeier, D. D., Samani, Z., Garrot Jr., D., Ray, D. T., Fangmeier, D. D., Samani, Z., Garrot Jr., D., & Ray, D. T. (1984). WATER REQUIREMENTS OF GUAYULE FOR RUBBER PRODUCTION.. Paper - American Society of Agricultural Engineers.
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  Abstract: Guayule Parthenium argentatum Gray was transplanted in April and October 1980 near Litchfield Park west of Phoenix, Arizona. Four irrigation application depths were applied to plots in a randomized block design. Shrubs were harvested in June 1982, Winter 1982-83, and January 1984. Dry matter produced, rubber content and rubber yield were determined. Average dry matter production increased with increasing water. Average rubber content decreased with increasing water. Average rubber content decreased with increasing water. Average rubber yield showed a slight increase with increasing water. An economic analysis showed guayule is not economical to product at current rubber prices.
• Ray, D. T. (1984). Metaphase I configurations of the reciprocal translocations in a cytogenetic tester set of Gossypium hirsutum L. Journal of Heredity, 75(5), 371-377.
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  Abstract: Twenty reciprocal translocations of the cytogenetic tester set of G. hirsutum were cytologically characterized. Nineteen of the 20 heterozygous translocations had a modal chiasma frequency of four per quadrivalent, 14 of which formed predominantly ring multivalents without interstitial chiasmata and five usually formed ring multivalents with at least one interstitial chiasma at MI. The remaining translocation averaged 3.27 chiasmata per quadrivalent and oriented predominantly as an alternate chain. Ten of the 20 reciprocal translocations formed predominantly alternate orientations at MI. Eight of these 10 lines were reciprocal translocations between two large A subgenome chromosomes. This suggests that the large A subgenome chromosomes allow the quadrivalent to be more flexible, resulting in easy reorientation to the stable alternate configuration. The constraints imposed by the chiasmata within the chromosome arms also appear to influence the orientation of the centromeres in quadrivalents at MI. Lines, In which a high frequency of multivalents with interstitial chiasma were observed, had a significantly lower frequency of multivalents with either one or two centromeres not involved in spindle attachment or with 3:1 orientations. © 1984, American Genetic Association.
• Ray, D. T., & Endrizzi, J. E. (1982). A tester-set of translocations in Gossypium hirsutum L. Journal of Heredity, 73(6), 429-433.
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  Abstract: The chromosomes in 62 translocations of Gossyplum hirsutum L. were identi fied over a period of years by Dr. M. S. Brown in Texas. The use of some of these translocation lines has given conflicting results, Indicating that either the chromosomes in certain lines were identified incorrectly, or that the purity or lineage of the seed lines is questionable. A tester-set consisting of 20 translocation lines, which identifies all 26 chromosomes of cotton, was selected for reidentificatlon of their chromosomes. Results showed that, except for one line, the chromosomes involved in each translocation of the tester-set were the same as originally identified. © 1982, American Genetic Association.

Presentations

• Mealing, V. S., Sproul, E., Summers, H., Elshikha, D., Wang, S., Ray, D. T., Teetor, V. H., Dierig, D. A., Dittmar, S., & Landis, A. E. (2021, June). Using Monte Carlo Analysis to Support Field Data Integration into LCAs. International Symposium on Sustainable Systems and Technology. Virtual: ISSST Network.
• Ray, D. T. (2020, June 1). How STEM Skills are Put to Use in Solving Problems or for Innovation. AZ 4-H Summit. Tucson (Virtual): University of Arizona Cooperative Extension: 4-H Youth Development.
• Wang, G. (., Dierig, D., & Ray, D. T. (2019, September 11). Guayule Response to Plant Population. AAIC 2019 Annual Meeting. Tucson, Arizona: Association for the Advancement of Industrial Crops.
• Ray, D. T. (2018, July 30 - August 3). The Use of Student Preceptors to Make a Large Class Smaller. Annual Conference, 2018, American Society for Horticultural Science. Washington DC: American Society for Horticultural Science.
• Ray, D. T. (2017, September 19-22). Thoughts on Integrating Your Teaching, Research, Extension, and Service. 2017 ASHS Annual Conference. Waikoloa Hawaii: American Society for Horticultural Science.
• Pantell, A., Park, S., Cruz, V. M., Ray, D. T., Niaura, W. S., & Dierig, D. A. (2016, Fall). Rate of Apomixis in USDA Germplasm for Guayule Breeding. AAIC 2016: International Conference: Industrial Crops: Promoting Sustainability, September 24-28, 2016. Rochester, New York: Association for the Advancement of Industrial Crops.
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  From our work with Bridgestone Americas, Inc.
• Ray, D. T., Winzerling, J., & Staten, M. (2016, Summer). Career Skills: Our Process and Wher We are Today. American Society for Horticultural Science, Annual Conference, August 8-11, 2016. Atlanta, Georgia: American Society for Horticultural Science.
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  Invited Talk: Workshop - Developing Soft Skills in Tomorrow's LeadersSponsored by the Teaching Methods Working Group
• Teetor, V. H., Schmalzel, C., & Ray, D. T. (2016, Fall). Planting Sweet Sorghum (Sorghum bicolor [L.] Moench) in Clumps Reduces Lodging but not Yields. AAIC 2016, International Conference, Industrial Crops: Promoting Sustainability, September 24-28, 2016. Rochester, New York: Association for the Advancement of Industrial Crops.
• Ray, D. T. (2015, January 27). School of Plant Sciences Faculty Research Overviews. The School of Plant Sciences Interdisciplinary Seminar Series. Marley 230: School of Plant Sciences.
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  One of three Faculty Research Overviews, along with Eliot Herman and Mohammed Pessarakli.
• Ray, D. T. (2015, January 29). Developing New/Alternative Crops. Herbarium Lunch Seminar. UA Herbarium: UA Herbarium.
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  Research emphasizes evaluation and enhancement of new and/or underutilized plant germplasm suitable for cultivation in arid environments. Present focus is on the evaluation and development of new rubber and biofuel crops.
• Teetor, V. H., Schmalzel, C., & Ray, D. T. (2015, October 18-22). Stalk Size of Sweet Sorghum is Affected by Planting Arrangement. 27th Annual Meeting, Association for the Advancement of Industrial Crops. Lubbock, Texas: Association for the Advancement of Industrial Crops.
• Ray, D. T. (2013, December 16). The Status of the Guayule Breeding Program at the UA. USDA-ARS, ALARC Seminar Series.
• Ray, D. T. (2013, December 2). Guayule Breeding. School of Plant Sciences Faculty Research Forum.
• Ray, D. T. (2013, October 12-16). Advances in Guayule Breeding, Genetics and Agronomics. AAIC 25th Annual Meeting New Crops: Bioeneergy, Biomaterials, Food, and Health. Washington, D.C.: Association for the Advancement of Industrial Crops.
• Teetor, V. H., Johnson, D., Schmalzel, C., Rooney, W. L., & Ray, D. T. (2013, October 12-16). Evaluation of Sweet Sorghum Germplasm fo Maturity in Arizona. AAIC 25th Annual Meeting New Crops: Bioeneergy, Biomaterials, Food, and Health. Washington, D.C.: Association for the Advancement of Industrial Crops.
• Teetor, V. H., Schmalzel, C., & Ray, D. T. (2013, October 12-16). Varying Dates of Planting and Harvest to Maximize Productivity of Sweet Sorghum for Ethanol Production in Arizona. AAIC 25th Annual Meeting New Crops: Bioeneergy, Biomaterials, Food, and Health. Washington, D.C.: Association for the Advancement of Industrial Crops.
• Ray, D. T. (2012, February). Sweet Sorghum as a Potential Feedstock for Liquid Biofuel in Arizona: A Plant Scientist's Perspective. Honors Forum Lunch.

Poster Presentations

• Chen, Y., Dierig, D. A., Wang, S., Ray, D. T., Barberan, A., & Neilson, J. W. (2021, August). Using Network Analysis to Identify Critical Soil Microorganisms Associated with Guayule Growth Stages. 2021 SBAR Annual Retreat. Tucson, Arizona: Sustainable Bioeconomy for Arid Regions.
• Evancho, B., Schmalzel, C., Lewis, M., Teetor, V. H., & Ray, D. T. (2021, August). Response by Guayule to Nitrogen Fertilizer in a Semi-Hydroponic System. ASHS Annual Conference, August 5-9, 2021, Denver, Colorado. Denver, Colorado: American Society for Horticultural Science.
• Ray, D. T., Teetor, V. H., & Schmakzel, C. (2021, August). Guar as an Alternative Crop in Semi-Arid Areas of Arizona, New Mexico, and Texas. ASHS Annual Conference, August 5-9. Denver, Colorado: American Society for Horticultural Science.
• Dierig, D., Waller, P. M., Teegerstrom, T., Mccloskey, W. B., Ray, D. T., & Evancho, B. E. (2020, October). Guayule Production in the Arid Southwest. Arizona Cooperative Extension 2020 Virtual Conference. Virtual: Arizona Cooperative Extension.
• Lewis, M. D., Teetor, V. H., & Ray, D. T. (2020, August 10-13). Screening Guayule Germplasm for Tolerance to Salt Stress. ASHS Annual Conference. Virtual: American Society for Horticultural Science.
• Schmalzel, C., Teetor, V. H., & Ray, D. T. (2020, August 10-13). Performance of Guar Germplasm in Southern Arizona. ASHS Annual Conference. Virtual: American Society for Horticultural Science.
• Evancho, B., Moreno, L., Peck, A., Judkins, A., Salas, J., Pearson, L., Chaney, C., Schmalzel, C., Teetor, V., & Ray, D. T. (2019, September 12). Guayule Root Morphological Differences Induced by Planting Methods. SBAR 2019 Annual Retreat. Tucson, Arizona: Sustainable Bioeconomy for Arid Regions.
• Evancho, B., Rock, C., Dery, J. L., & Ray, D. T. (2019, July 23, 2019). Changing Agriculture in the Southwestern United States: A Survey of the Arizona Agriculture Community. ASHS 2019 Annual Conference. Las Vegas, Nevada: American Society for Horticultural Science.
• Lewis, M., Judkins, A., Teetor, V., & Ray, D. T. (2019, September 12). Evaluating Guayule Germplasm for Salt Tolerance. SBAR 2019 Annual Retreat. Tucson, Arizona: Sustainable Bioeconomy for Arid Regions.
• Godfrey, D., Bennett, M., Willmon, J., Waltz, Q., Coronado, G., Teetor, V., Schmazel, C., & Ray, D. T. (2018, August 1 - August 3). Vegetative Propagation in Parthenium argentatum (Gray). Sustainable Bioeconomy for Arid Regions. Tucson, AZ: National Institute for Food and Agriculture.
• Willmon, J., Hu, J., Teetor, V. H., & Ray, D. T. (2018, July 30 - August 3). Screening Parthenium argentatum for resistance to Phymatotrichum omnivorum. Annual Conference, 2018, American Society for Horticultural Science. Washington DC: American Society for Horticultural Science.
• Teetor, V. H., Main, M., Majeau, G., & Ray, D. T. (2017, September 19-22). Farm to Fuel: Guayule as a Feedstock for a Sustainable Bioeconomy in Arid Regions. 2017 ASHS Annual Conference. Waikoloa, Hawaii: American Society for Horticultural Science.
• Ray, D. T., Teetor, V. H., & Schmalzel, C. (2016, Summer). Are There Advantages to Altering Planting Arrangement of Sweet Sorghum?. American Society for Horticultural Science, Annual Conference, August 8-11, 2016. Atlanta, Georgia: American Society for Horticultural Science.
• Ray, D. T., Teetor, V. H., & Schmalzel, C. (2015, August 4-7). Planting Method Affects Stalk Size in Sweet Sorghum. ASHS 2015 Annual Conference. New Orleans, LA: American Society for Horticultural Sciences.
• Teetor, V. H., & Ray, D. T. (2015, October 29). Stalk Size Affected by Planting Method in Sweet Sorghum. 2015 CALS Poster Forum. UA Student Union Ballroom: Reseach Administration, CALS.
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  The goal of this event is to showcase all projects at CALS, including work done in academic departments and extension, and to foster collaboration.
• Spanier, A., Hought, J., Steen, C., Teetor, V. H., & Ray, D. T. (2014, July 28-3`1, 2014). Clonal Propagation of Guayule through Cuttings. Annual Conference of the American Society for Horticultural Science. Orlando, Florida.
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  I was the presenting author.
• Spanier, A., Ray, D. T., & Steen, C. (2014, January 25, 2014). Guayule Clone Propagation through Cuttings. Undergraduate Biology Research Program. Tucson, AZ: Undergraduate Biology Research Program.
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  This was Adam's UBRP project and the was the presenter.
• Ray, D. T., Teetor, V. H., Johnson, D., & Schmalzel, C. L. (2013, July 22-25). Evaluating Sweet Sorghum Germplasm for Maturity in Arizona. ASHS Annual Conference. Palm Desert, California: American Society for Horticultural Science.
• Stover, M. G., Teetor, V. H., Johnson, D. J., & Ray, D. T. (2013, January 19). Evaluation of Sugar Content in Sweet Sorghum Exposed to Water Stress over Time. 24th Conference of the Undergraduate Biology Research ProgramUndergraduate Biology Research Program.
• Wang, G. (., Wang, G. (., McCloskey, W. B., McCloskey, W. B., Bronson, K., Bronson, K., Thorp, K., Thorp, K., Ray, D. T., & Ray, D. T. (2013, July 22-25). Lesquerella Yield and Oil Quality Response to N Fertilizer Rate and Irrigation. ASHS Annual Conference. Palm Desert, California: American Society for Horticultural Science.

Others

• Ogden, K., Ray, D. T., Chavarria, S., & Dierig, D. A. (2022, January). Guayule-based Job Creation in the Arid Regions' Bioeconomy. SBAR Center for Excellence Briefing Paper.
• Dierig, D. A., Cruz, V. M., Abdel-Haleem, H., Evancho, B., Wang, S., Heinitz, C., & Ray, D. T. (2021, November). Comprehensive Evaluation of USDA Germplasm in Arizona. SBAR Fact Sheet.
• Idowu, J., Angadi, S., & Ray, D. T. (2021, March). Guar as a Rotation Crop. SBAR Fact Sheet.
• Idowu, J., Ray, D. T., Cruz, V. M., & Dierig, D. A. (2021, October). Guayule Growing Range Expansion in the Southwest. SBAR Center of Excellence Briefing Paper.
• Ogden, K., Ray, D. T., Chavarria, S., & Dierig, D. A. (2021, December). Guayule-based Job Creation in the Arid Regions' Bioeconomy. SBAR Center of Excellence Briefing Paper.
• Ogden, K., Ray, D. T., Chavarria, S., & Dierig, D. A. (2021, October). Sustainable Bio-economy for Arid Regions. SBAR Center of Excellence Briefing Paper.
• Rom, C. R., Ray, D. T., Sams, C., Santos, K., Dickson, R., Campbell, C., Campbell, R., Stover, E., Reiger, M., Olmstead, M., McCollum, L., Kopsell, D., & Kopsell, D. (2018, July 30). Creating Your Future: Strategic Planning Forum. Annual Conference, 2018, American Society for Horticultural Science.
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  Session for undergraduate and graduate students, attending the 2018 ASHS Annual Conference, on career planning. I was involved in planning, moderating, and presenting at the session.
• Shotwell, M., Ray, D., Shotwell, M., & Ray, D. (2011, Fall). Genetics: Laboratory Manual (Second Edition). Kendall/Hunt Publishing Company.
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  Pages 1-214