Jiahuai Hu

Interests

Teaching

Plant Disease Diagnosis, Plant Disease Management

Research

Etiology, biology, and epidemiology of phytopathogenic fungi , bacteria, nematodes and virusesDevelopment, validation and implementation of existing and new plant disease diagnostic toolsBiological, cultural and chemical management of crop diseases

Courses

Scholarly Contributions

Journals/Publications

• Hu, J. (2024). First Report of Causing Rubbery Rot on Potato in Arizona. Plant disease.
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  In January 2023, stand loss due to seed decay (
• Faske, T., Hu, J., Mueller, J., Becker, O., Bradley, C., Bernard, E., Bond, J., Desager, J., Gorny, A., Grabau, Z., Kemerait, R., Koehler, A., Lawrence, K., Sikora, E., Thomas, S., Walker, N., Wheeler, T., Ye, W., & Zhang, L. (2023). Summarized distribution of the southern root-knot nematode, Meloidogyne incognita, in field crops in the United States. Plant Health Progress. doi:https://doi.org/10.1094/PHP-04-23-0031-BR
• Hu, J. (2023). First Report of Causing Sooty Spot on Postharvest Clementines in the United States. Plant disease.
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  In 2022, post-harvest symptoms of black spots were observed at an incidence of 2-5% on easy peeling clementines (citrus × clementina) in a fresh fruit market in Phoenix metropolitan area, Arizona. Black lesions on the fruit rind were superficial, circular, dry, and firm with gray sporulation. Gray or black aerial mycelium was also noticed on top of the black spots. Black spots were distributed over the entire fruit surface without any regular patterns. Maceration of rind and flesh was also noticed under refrigerated storage conditions. Two isolates were obtained (S13 and S14) and cultured on potato dextrose agar (PDA) at 25oC for 14 days. The colony color and texture of both isolates were identical on PDA: olivaceous black with abundant sporulation, margin entire edge to slightly undulate. Conidia were 0-1 septate and globose or ellipsoid with sizes ranging from 4-10 × 2-4 μm (n = 15). Ramoconida were also 0-1 septate and ellipsoid to cylindrical with sizes ranging from 15-30 × 2-5 μm (n = 15). Conidiophore had a width of 3-6 μm (n = 15). Isolates were identified as Cladosporium ramotenellum based on these morphological features (Bensch et al. 2012). The IDs of these two isolates were further confirmed by genomic DNA isolation, PCR amplification and sequencing of the ITS1-5S-ITS2-28S region of rDNA (V9G/LR5 de Hoog and Gerrits van den 1998, primers ITS4/ITS5 White et al.), actin gene (ACT-512F/ACT-783R, Carbone and Kohn 1999), and elongation factor 1α gene (EF1-1018F/EF1-1620R, Stielow 2015). Sequences of the two isolates were identical and thus only one sequence of each gene was deposited in the GenBank. A BLASTn search of actin sequence (233-bp, OQ185511) revealed 99.1% match with ex-type sequence EF 679538 (strain CBS:121628) of C. ramotenellum holotype (query coverage: 97%). BLASTn analysis of a portion of EF-1α gene (579-bp, OQ185512) revealed more than 99.7% similarity with sequences KU933429 (ATCC strain 16022) and MT881827 (strain 18EPLE003) of C. ramotenellum (query coverage: 100%). The ITS sequence (1519-bp, OQ236707) was identical to the ITS sequences of C. ramotenellum strains in easy peeler mandarins from Peru (Murciano et al. 2021). Pathogenicity tests were carried out twice on fresh easy-peeling clementine fruit. The inocula (1 x 105 spores/ml) were prepared in sterile distilled water containing 0.1% Tween 20 (TW) by mixing the conidial suspensions of two isolates from 7-day-old PDA cultures. Ten fruit were washed, surface sanitized with 70% ethanol, and wound-inoculated by immersing five fruit in spore suspension for 1 min. Five control fruit were wound-inoculated with TW. Inoculated and control fruit were stored in separate zip-lock bags for one week. Black spots resembling those observed on naturally infected fruit were present on inoculated fruit, while control fruit remained symptomless. C. ramotenellum was reisolated and was morphologically identical to the original isolates, thus completing Koch's postulates. C. ramotenellum has been reported as a fungal pathogen causing sooty spots on easy peeler mandarins from Peru (Murciano et al. 2021). To our knowledge, this is the first report of C. ramotenellum causing postharvest sooty spot and decay on clementines in the United States. Results show that infected fruit is potentially a pathogen source for long-distance dispersal. This occurrence was communicated to the state regulatory agencies for regulatory actions on imports of citrus fruit from countries with the occurrence of C. ramotenellum.
• Hu, J. (2022). Detection of Seiridium cardinale causing bark cankers on Leyland cypress (x Cupressocyparis leylandii) in Arizona. Plant Health Progress. doi:https://doi.org/10.1094/PHP-04-22-0039-BR
• Hu, J. (2022). Occurrence of Grapevine Red Blotch Virus in Wine Grapes in Arizona. Plant Health Progress. doi:https://doi.org/10.1094/PHP-03-22-0030-BR
• Hu, J. (2022). First report of Globisporangium heterothallicum causing seedling disease on guayule in Arizona. Plant disease.
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  Guayule (Parthenium argentatum A. Gray) is known for producing low-allergenic latex that is used in high end rubber products for medical use such as rubber gloves, catheters, and condoms. Currently, there are growing efforts from tire industry to commercialize guayule for rubber production in Arizona. During May 2019, wilting and death of c. 25% of seedling plants were observed in direct-seeded guayule fields in central Arizona. Symptoms of root rots and hypocotyl constriction were observed on affected seedling plants. To identify the causal agent, four symptomatic plants were collected to isolate the putative pathogen. Small pieces of symptomatic root (2-5 mm) were surface sterilized in 0.6% sodium hypochlorite for 1 min, rinsed copiously in sterile distilled water, blotted dry, and plated on 10% clarified V8-PARP (Jeffers and Martin 1986). Four oomycete-like isolates with abundant hyphal swellings were purified by transferring tips of single hypha onto new 20% CV8 plates and incubating at 23°C for one week. Sporangia were formed abundantly, globose or lemon-shaped (average 20 ± 4 × 20 ± 4 μm, n = 15). Isolates did not produce oospores (heterothallic). Genomic DNA was extracted from the mycelia of two isolates using DNeasy Plant Pro Kit (Qiagen Inc., Valencia, CA) according to the manufacturer's instructions. The internal transcribed spacer (ITS) region of rDNA and mitochondrially encoded cytochrome c oxidase 1 (cox 1) gene were amplified with primers ITS1/ITS4 (White et al., 1990) and OomCoxI-Levup/OomCoxI-Levlo (Martin and Tooley, 2003; Robideau et al., 2011) and the resulting amplicons were sequenced (GenBank Accession No. OL514636 and OL539842). A BLASTn search of 808-bp amplicon (OL514636) revealed 100% match with ITS sequences MT039880 which was G. heterothallicum causing root and crown rot of pepper in Turkey. BLAST analysis of the 658-bp amplicon (OL539842) showed 99.39 % identity with the COX 1 sequence of G. heterothallicum from tomato in Australia (MT981128). To fulfill Koch's postulates, pathogenicity tests were conducted twice on 2-week-old 'Az 2' guayule plants grown in 1.9-liter pots filled with a steam-disinfested potting mix. Pots were placed in a plastic container and watered three times a week by flooding, to create waterlogged conditions. Plants were maintained in a greenhouse and fertilized weekly with a 20-20-20 fertilizer at 1mg/ml. Twenty plants in 5 pots (4 plants/pot) were challenged with a G. heterothallicum isolate by drenching pot with 50 ml of a 1×106 zoospore/ml suspension. Twenty plants in 5 pots, serving as a control, received each 50 ml of distilled water. Symptoms of wilting and water-soaked root rot, and plant death were observed 2 weeks afterward, whereas control plants remained asymptomatic. G. heterothallicum was reisolated from necrotic roots of inoculated plants but not from control plants. G. heterothallicum has been increasingly reported as a pathogen of damping-off or root and crown rot on hosts such as alfalfa in Minnesota (Berg et al., 2017), soybean in Pennsylvania (Coffua et al., 2016), spinach in Sweden (Larsson, 1994), corn in China (Gan, et al., 2010), pepper in Turkey (Dervis, et al., 2020). To our knowledge, this is the first report of G. heterothallicum causing guayule seedling diseases in the United States. The presence of broad-host-range pathogen G. heterothallicum suggests that new strategies are needed for managing this pathogen to increase stands in direct-seeded guayule production system.
• Sanogo, S., Lamour, K., Kousik, S., Lozada, D. N., Parada Rojas, C. H., Quesada-Ocampo, L., Wyenandt, C. A., Babadoost, M., Hausbeck, M. K., Hansen, Z., Ali, E., McGrath, M., Hu, J., Crosby, K., & Miller, S. A. (2022). Phytophthora capsici, 100 Years Later: Research Mile Markers from 1922 to 2022. Phytopathology.
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  In 1922, was described by Leon Hatching Leonian as a new pathogen infecting pepper ( L.), with disease symptoms of root rot, stem and fruit blight, seed rot, and plant wilting and death. Extensive research has been conducted on over the last 100 years. This review succinctly describes the salient mile markers of research on with current perspectives on the pathogen's distribution, economic importance, epidemiology, genetics and genomics, fungicide resistance, host susceptibility, pathogenicity mechanisms, and management.
• Wright, G. C., & Hu, J. (2021). Canker and Wood Rot Pathogens in Southwest Arizona Lemon Orchards. Plant Pathology, 15. doi:https://doi.org/10.1111/ppa.13476
• Faske, T. R., Kandel, Y. R., Allen, T., Grabau, Z., Hu, J., Kemerait, R., Lawrence, G., Lawrence, K. S., Mehl, H. L., Overstreet, C., Thiessen, L., & Wheeler, T. A. (2022). Meta-analysis of the field efficacy of seed- and soil-applied nematicides on and across the U. S. Cotton Belt. Plant disease.
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  Meta-analysis was used to compare yield protection and nematode suppression provided by two, seed- and two, soil-applied nematicides against and on cotton across three years and several trial locations in the United States Cotton Belt. Nematicides consisted of thiodicarb- and fluopyram-treated seed, aldicarb and fluopyram applied in-furrow and combinations of the seed treatments and soil-applied fluopyram. The nematicides had no effect on nematode reproduction or root infection but had a significant impact on seed cotton yield response (¯D) with an average increase of 176 and 197 kg/ha relative to the nontreated control in M. incognita and R. reniformis infested fields, respectively. However, because of significant variation in yield protection and nematode suppression by nematicides, five or six moderator variables [cultivar resistance (M. incognita only), nematode infestation level, nematicide treatment, application method, trial location, and growing season] were used depending on nematode species. In infested fields, greater yield protection was observed with nematicides applied in-furrow and seed-applied + in-furrow than solo seed-applied nematicide applications. Most notably of these in-furrow nematicides were aldicarb and fluopyram (>131 g/ha) with or without a seed-applied nematicide compared to thiodicarb. In infested fields, moderator variables provided no further explanation of the variation in yield response by nematicides. Furthermore, moderator variables provided little explanation of the variation in nematode suppression by nematicides in and infested fields. The limited explanation by the moderator variables on the field efficacy of nematicides in and infested fields demonstrates the difficulty of managing these pathogens with nonfumigant nematicides across the U. S. Cotton Belt.
• Hu, J. (2021). A selective medium for the recovery and enumeration of Fomitopsis meliae from lemon orchards. Plant Health Progress, 10. doi:https://doi.org/10.1094/PHP-10-21-0124-RS
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  A selective medium (FMS medium) was developed for the isolation and quantification of Fomitopsis meliae, the causal agent of lemon canker and brown wood rot, from plants, soil, and air. The optimal concentration and combination of fungicides and antibiotics was evaluated to determine the most selective condition for growing F. meliae. The resultant composition of the medium (FMS) per litre (pH 3.5) was: 16 mg thiophanate-methyl, 8 mg dichloran, 5 mg 2-phenylphenol, 100 mg fluopyram, 0.5 mg fludioxonil, 100 mg chloramphenicol, 100 mg streptomycin, 15 g malt extract, 2.5 g mycological peptone, and 15 g agar. The fungus was successfully isolated and enumerated from air, soil and plant tissues using FMS medium. Furthermore, FMS medium almost completely inhibited the growth of other plant pathogenic fungi, soil and air saprophytes. This selectivity was high enough to estimate spore inoculum of F. meliae in an air sample or as a spore trapping device in commercial lemon orchards. FMS medium will be useful for studying epidemiology and management of F. meliae.
• Hu, J. (2021). Cotton Root Rot. University of Arizona Cooperative Extension Publication, 4. doi:https://extension.arizona.edu/pubs/cotton-root-rot
• Hu, J. (2021). First Report of 'Candidatus Phytoplasma trifolii' Related Strain Associated with Yellowing and Witches'-Broom of Industrial Hemp (Cannabis sativa) in Arizona. Plant disease.
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  In Arizona, industrial hemp (Cannabis sativa) is a newly cultivated crop for fiber, oil, cosmetic products, and health food. During July to September 2020, two fields of industrial hemp crops were identified in southern Arizona with 10 to 30% incidence of plants showing witches' broom. Disease incidence was assessed by counting symptomatic plants in 4 randomly selected rows of 25 plants in each field. Symptoms ranged from leaf mottling and yellowing on mildly affected plants to leaf curling and shortened internode length of stem on severely affected plants (Fig. 1). Shoots were randomly collected from eight symptomatic plants and three asymptomatic plants in the same area. Genomic DNA was extracted from 200 mg of each sample using DNeasy Plant Pro Kit (Qiagen Inc., Valencia, CA) according to the manufacturer's instructions. Phytoplasma was tested by a real-time PCR assay and TaqMan probe targeting the 23S ribosomal RNA gene that detects a wide range of known Phytoplasmas (Hodgetts et al., 2009). Beet curly top virus (BCTV) was targeted using BCTV-specific primers BCTV1 and BCTV2 following a method by Rondon (Rondon et al., 2016). BCTV was not detected in the plants, but Phytoplasmas were detected in all eight symptomatic plants, but not in the three control plants. The positive DNA samples were used to identify the phytoplasma by nested PCR using universal phytoplasma-specific primer pairs P1/P6 (Deng, S. et al. 1991) and R16F2n/R16R2 (Gundersen et al., 1996) targeting the 16S rRNA gene and the resulting 1.25 kb fragment in 4 positive samples was subjected to Sanger sequencing (Eton Bioscience, San Diego). All 4 sequences were identical and deposited in GenBank under accession MW981356. BLASTn results indicated 100% identity with that of several 'Candidatus Phytoplasma trifolii' strains on potato (KR072666, KF178706) in Washington and chile peppers (HQ436488) in New Mexico. It also shared 99.84% identity with the sequence of the reference strain of Candidatus Phytoplasma trifolii' (AY390261) that caused clover proliferation. The phytoplasma AZH1 was classified as a member of subgroup A within group16SrVI using iPhyClassifier, an interactive online tool for phytoplasma classification and taxonomic assignment (Zhao et al., 2013). Phylogenetic analysis revealed that the phytoplasma AZH1 clustered with other isolates of 'Candidatus Phytoplasma trifolii' (Fig. 2), including the strain NV1 associated with witches' broom on C. sativa in Nevada (Feng et al. 2019). This is the first report of 'Candidatus Phytoplasma trifolii' related strain associated with yellowing and witches' broom on hemp in Arizona. This finding is significant as the observation of symptoms at 30% incidence in one field suggested that the identified pathogen may pose a significant threat to the production of industrial hemp production in Arizona.
• Hu, J. (2021). First Report of Crown and Root Rot Caused by Pythium myriotylum on Hemp (Cannabis sativa) in Arizona. Plant disease.
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  During August and September 2020, symptoms of leaf chlorosis, stunting, and wilting were observed on indoor hemp plants (Cannabis sativa L. cv. 'Wedding Cake') in a commercial indoor facility located in Coolidge, Arizona. Plants were grown in soilless coconut coir growing medium (Worm Factory COIR250G10), watered with 1.5 to 2.1 liters every 24 h through drip irrigation, and supplemented with 18 h of lighting. About 35% of plants displayed symptoms as described above and many symptomatic plants collapsed. To identify the causal agent, crown and root tissues from four symptomatic plants were harvested and rinsed with tap water. Tissue fragments (approx. 2 to 4 mm in size) were excised from the margins of the stem and root lesions, surface sterilized in 0.6% sodium hypochlorite for 1 min, rinsed well in sterile distilled water, blotted dry, and plated on potato dextrose agar (PDA) and on oomycete-selective clarified V8 media containing pimaricin, ampicillin, rifampicin, and pentachloronitrobenzene (PARP). Plates were incubated at room temperature (21-24 oC). Five isolates resembling Pythium were transferred after 3 days and maintained on clarified V8 media. Morphological characteristics were observed on grass blade cultures (Waterhouse 1967). Grass blades were placed on CV8 inoculated with the isolate. After a 1-day incubation at 25°C, the colonized blades were transferred to 8 ml of soil water extract in a Petri dish. Ten sporangia and oogonia were selected randomly and their diameters were measured under the microscope. Sporangia were mostly filamentous, undifferentiated or inflated lobulate, ranging from 7 to 17 µm in diameter. Knob-like appressoria were observed on branching clusters. Bulbous-like antheridia were formed on branched stalk with 1-8 antheridia per oogonium. Globose oogonia were terminal or intercalary and ranged from 21 to 33 µm in diameter. Globose oospores were mostly aplerotic and ranged from 15 to 21 μm in diameter. Based on these morphological characteristics, isolates were tentatively identified as Pythium myriotylum (Watanabe, 2002). Genomic DNA was extracted from mycelial mats of two isolates using DNeasy Plant Pro Kit (Qiagen Inc., Valencia, CA) according to the manufacturer's instructions. The internal transcribed spacer (ITS) region of rDNA was amplified with primers ITS1/ITS4 and two identical nucleotide sequences were obtained and deposited under accession number MW380925. A BLASTn search revealed ≥ 98% query coverage and 100% match with sequences HQ237488.1, KY019264.1, and KM434129, which were isolates of P. myriotylum from palm, tobacco, and ginger, respectively. To fulfill Koch's postulates, pathogenicity tests were conducted with 2 isolates using plants of 'Wedding Cake' grown in 12 1.9-liter pots filled with a steam-disinfested potting mix (Sungro Professional Growing Mix). Pots were placed in a plastic container and watered to flooding three times a week. Plants were maintained in a greenhouse with 18 h/10 h day/night supplemental light cycle (15-28 oC). Plants were fertilized weekly with Peters Professional fertilizer at 1mg/ml. Four plants were inoculated with each isolate at three weeks after seed sowing by placing two 5-mm mycelial plugs from active growing 4 days-old cultures on PDA media adjacent to the main root mass at an approximately 3 cm depth. Four plants were inoculated with blank PDA plugs as controls. Symptoms of leaf chlorosis, crown rot and wilting were observed after four weeks while control plants remained symptomless. P. myriotylum was re-isolated from necrotic roots of inoculated plants after surface-sterilization, but not from control plants. The pathogenicity test was repeated once. While P. myriotylum often occurs in warmer regions and has a wide host range of >100 host plant species including numerous economically important crops (Wang et al., 2003), there are only two reports of this pathogen on indoor hemp plants in a greenhouse in Connecticut (McGehee et al., 2019) and in Canada (Punja et al., 2019). This is the first report of P. myriotylum causing root and crown rot of indoor hemp in Arizona. A more careful water management in soilless growth medium to reduce periods of saturation would minimize the risk of Pythium root rot in indoor hemp production.
• Hu, J. (2021). Verticillium wilt of cotton. University of Arizona Cooperative Extension Publication, 7. doi:https://extension.arizona.edu/pubs/verticillium-wilt-cotton
• Hu, J. (2021). Verticillium wilt of pistachio. University of Arizona Cooperative Extension Publication, 4. doi:https://extension.arizona.edu/pubs/verticillium-wilt-pistachio
• Hu, J., & Masson, R. (2021). Beet curly top virus of industrial hemp. University of Arizona Cooperative Extension Publication, 8. doi:https://extension.arizona.edu/pubs/beet-curly-top-virus-industrial-hemp
• Hu, J., & Masson, R. (2021). First Report of Crown and Root Rot Caused by Pythium aphanidermatum on Industrial Hemp (Cannabis sativa) in Arizona. Plant disease, 105(8), 2. doi:https://doi.org/10.1094/PDIS-01-21-0065-PDN
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  During July and August 2020, symptoms of leaf yellowing and browning, sudden wilting, and death were observed on industrial hemp plants (Cannabis sativa L.) in several drip-irrigated fields in Yuma and Graham county, Arizona. About 85% of plants showed severe crown and root rot symptoms. A high percentage of affected plants collapsed under intensive heat stress. Shriveled stem tissue with necrotic lesions can often be seen at the base of the plant, extending upwards more than 5 cm. Internal tissue of main stem and branches was darkened or pinkish brown. Outer cortex of root bark was often completely rotten, exposing the white core. Cottony aerial mycelium was visible on the surface of stalk of some of the infected plants in two fields in Yuma. To identify the causal agent, a total of twenty symptomatic plants were collected from several fields across the state. Crown and root tissues from affected plants were harvested and rinsed in tap water to remove soils. Approximately 2 to 4 mm tissue fragments were excised from the margins of the affected stem and root lesions, surface sterilized in 0.6% sodium hypochlorite for 1 min, rinsed copiously in sterile distilled water, blotted dry, and plated on potato dextrose agar (PDA), and on oomycete-selective clarified V8 medium containing pimaricin, ampicillin, rifampicin, and pentachloronitrobenzene (PARP). Plates were incubated at room temperature for 2 days. Sixteen isolates were recovered and their mycelial colonies resembled the morphology of Pythium. Based on the culture morphology on V8 medium, all isolates were tentatively identified as P. aphanidermatum with fast-growing, aseptate hyphae ranging from 3 to 7 μm in width, globose oogonia ranging from 25 to 31 μm in diameter, barrel-shaped antheridia, globose oospores ranging from 15 to 21 μm in diameter (10 measurements) (Watanabe, 2002). Genomic DNA was extracted from mycelial mats of three isolates using DNeasy Plant Pro Kit (Qiagen Inc., Valencia, CA) according to the manufacturer's instructions. The internal transcribed spacer (ITS) region of rDNA was amplified with primers ITS1/ITS4 and three nucleotide sequences were obtained. All three sequences were identical and deposited under accession number MW380253 in GenBank. A BLASTn search revealed that MW380253 had a 100% query coverage and 100% match with sequences MK611609.1, KJ162355.1, and AY598622.2, obtained from isolates of P. aphanidermatum. To fulfill Koch's postulates, pathogenicity tests were conducted with 2 isolates using 12 seeds of a hemp line 14 sown in 12 1.9-liter pots filled with a steam-disinfested potting mix. Pots were placed in a plastic container and watered three times a week by flooding, to create waterlogged conditions. Plants were maintained in a greenhouse supplemented with artificial lighting of 14 h/10 h day/night light cycle. Plants were fertilized weekly with a 20-20-20 fertilizer at 1mg/ml. Three weeks after sowing, four plants were inoculated with each isolate by drenching each plant with 200 ml of a 1×105 zoospore/ml suspension. Four plants, serving as control, received each 200 ml of distilled water. Symptoms of leaf chlorosis, crown and root rot, and wilting were observed 3 weeks afterwards, while control plants remained asymptomatic. P. aphanidermatum were re-isolated from necrotic roots of inoculated plants, but not from control plants. P. aphanidermatum was previously detected on industrial hemp in a research plot in Indiana (Beckerman et al., 2017) and is also known to affect other crops in Arizona during the summer months as well (Olsen & Nischwitz, 2011). This report is the first publication documenting P. aphanidermatum on field grown hemp in Arizona. Industrial hemp (Cannabis sativa) is an emerging crop in Arizona. The first plantings of hemp were in June of 2019, where 5,430 acres of hemp was planted in thirteen counties in Arizona before the end of the year. The Arizona Department of Agriculture Industrial Hemp Program, 2019 Year End Report confirms that nearly one-quarter of all hemp planted in 2019 did not receive a final state inspection due to crop loss. This disease is a potential constraint to hemp production in hot, arid climates, where copious water is used in combination with plastic mulch and/or drainage is poor.
• Hu, J., & Masson, R. (2021). Pythium crown and root rot of industrial hemp. University of Arizona Cooperative Extension Publication, 4. doi:https://extension.arizona.edu/pubs/pythium-crown-root-rot-industrial-hemp
• Hu, J., & Rueda, A. (2022). First Report of Phytophthora parsiana Causing Crown and Root Rot on Guayule in the United States. Plant disease, 2. doi:https://doi.org/10.1094/PDIS-10-21-2239-PDN
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  Guayule (Parthenium argentatum A. Gray) is a perennial shrub plant (approximately 50 cm in height) cultivated in the southwestern United States. It produces natural low-allergenic latex, resins and high-energy biofuel feedstock. During August 2021, a crown and root rot disease was observed on 2-year-old plants of direct-seeded guayule cultivar 'Az 2' in research plots located in Pinal county, Arizona, where a record 36 cm of rainfall fell during monsoon season. Symptoms included yellowing of leaves, wilting, and plant death. Average disease incidence was 16%. Isolation from necrotic crown and root tissues on 10% clarified V8-PARP (Jeffers and Martin 1986) yielded Phytophthora-like colonies. Three isolates were subcultured on V8 agar and chlamydospores and hyphal swellings were abundant in 2-week-old cultures. All three isolates produced abundant noncaducous and nonpapillate sporangia ranging from 33 to 54 μm × 20 to 39 μm (average 45.5 × 28.5 μm, n = 20) in soil water extract solution. Isolates did not produce oospores after 2 weeks on carrot agar at 20°C in the dark. Isolates had optimum vegetative growth at 30 oC and grew well at 35 oC. There was no growth at 5 and 40 oC. Genomic DNA was extracted from the mycelia of three isolates using DNeasy Plant Pro Kit (Qiagen Inc., Valencia, CA) according to the manufacturer's instructions. The internal transcribed spacer (ITS) region of rDNA, mitochondrially encoded cytochrome c oxidase 1 (cox 1) gene, and beta-tubulin (β-tub) gene were amplified with primers ITS1/ITS4 (White et al., 1990), COXF4N/COXR4N and TUBUF2/TUBUR1 (Kroon et al., 2004) and the resulting 3 amplicons were sequenced (GenBank Accession No. OK438221, OK484426, and OK484427). A BLASTn search of 811-bp amplicon (OK438221) revealed 99% match (762/766) with ITS sequences MG865562 which was Phytophthora parsiana Ex-type CPHST BL 47 from Iran. BLAST analysis of the 867-bp amplicon (OK484427) showed 99% identity (866/867) with the COX 1 sequence of P. parsiana (KC733455) from Virginia. BLAST analysis of the 941-bp amplicon (OK484426) showed 99% identity (928/938) with the β-tub sequence of P. parsiana (AY659746). To fulfill Koch's postulates, pathogenicity tests were conducted twice on 2-week-old 'Az 2' guayule seedlings grown in 10 plants per 1.9-liter pot filled with a steam-disinfested potting mix. Pots were placed in a plastic container and watered three times a week by flooding, to create waterlogged conditions. Plants were maintained in a greenhouse with 12 h day/12 h night (15-28 oC) and fertilized weekly with a 20-20-20 fertilizer at 1mg/ml. Fifty plants in 5 pots were challenged with a P. parsiana isolate by drenching each pot with 50 ml of a 1×105 zoospore/ml suspension. Fifty plants in 5 pots, serving as a control, received each 50 ml of distilled water. Symptoms of wilting, root rot, and plant death were observed 1 week afterward in inoculated plants, whereas control plants remained asymptomatic. P. parsiana was reisolated from necrotic roots of inoculated plants but not from control plants. To our knowledge, this is the first report of crown and root rot in guayule caused by P. parsiana in Arizona. P. parsiana is a species known for causing root rot on woody plants such as pistachio in California (Fichtner et al., 2016) and Iran (Mostowfizadeh-Ghalamfarsa et al., 2008). Arizona is home of desert woody guayule plant. P. parsiana may represent a significant barrier to commercialization of guayule for rubber in low desert areas of Arizona. The origin, distribution, and virulence of the pathogen on Arizona guayule is currently unknown. Disease resistance evaluation may help identify resistance in guayule germplasm that are useful in breeding for resistant cultivars.
• Hu, J., & Schalau, J. W. (2021). First report of a ‘Candidatus Phytoplasma fraxini’-related strain associated with witches’-broom of Arizona ash. New Disease Reports, 44(e12023), 4. doi:https://doi.org/10.1002/ndr2.12023
• Hu, J., & Wright, G. (2021). First Report of Fomitopsis meliae Causing Brown Wood Rot on Living Lemon Trees in Arizona and California. Plant disease.
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  Arizona is one of the largest producers of premium lemons for fresh market in the world. In 2018, 54,000 metric tons of lemons were produced on more than 7,300 acres. In recent years, wood rot diseases have become increasingly important in desert citrus production, with an incidence rate of 70 to 100% in some lemon orchards in Yuma, and lower rates in lemon orchards in the California desert. In 2018 and 2019, A brown wood rot showing symptoms of leaf chlorosis, branch gummosis and wilt, and branch breakage was the most common disease in many lemon orchards. Where disease was observed, a white mycelial mass often covered split exposed internal wood and basidiocarps were found on fallen decaying wood on orchard floors. The fungal colony, consistently isolated from decaying wood on malt extract agar or potato dextrose agar (PDA), was white, dense, and cottony-floccose. The 7-day-old culture had a distinct mushroom odor and hyphae were hyaline, thin-walled, and clamped generative. Genomic DNA was extracted from the mycelia of three isolates using DNeasy Plant Pro Kit (Qiagen Inc., Valencia, CA) according to the manufacturer's instructions. The internal transcribed spacer (ITS) region of rDNA was amplified with primers ITS1/ITS4 (White et al., 1990). The resulting three nucleotide sequences were identical and deposited under accession number MW221272 in GenBank. A BLASTn search revealed 97.45% and 99.94% match with sequences HQ248221.1 and KT718002.1, respectively, which were isolates of Fomitopsis meliae with a query coverage at 100%. To fulfill Koch's postulates, pathogenicity tests were conducted on 30-year-old 'Lisbon' (Citrus x limon (L.) Osbeck) lemon trees at the Yuma Agriculture Center Mesa farm from February to July in 2019: ten branches (6-to-10 cm in diameter) from ten different trees were inoculated with each of three representative isolates. The inoculum was prepared by growing each isolate on wheat grains for three weeks at 23 to 25oC. Tree branches were inoculated by inserting five colonized wheat grains in 2-cm holes which were drilled into the branches and then covered with Parafilm. Five branches were inoculated with sterile grains and used as a control. Disease was assessed four months later by removing inoculated branches, splitting them in half through the inoculation point, and measuring the length of the wood area affected by wood rot. Brown discoloration of the wood extended an average of 3.9, 4.2, and 4.9 cm per isolate into wood tissues surrounding the inoculation hole, while control branches remained healthy. Fomitopsis meliae was consistently re-isolated from decayed wood based on morphology and ITS sequences. To our knowledge, this is the first report of brown wood rot caused by Fomitopsis meliae in lemon in Arizona and California. Fomitopsis species often attack conifers, hardwoods, and fruit trees (Adaskaveg et al., 1993, Gilbertson & Ryvarden, 1987). A species of Fomitopsis was detected in 40-year-old sweet orange trees and was highly pathogenic on lemons in southern Italy (Roccotelli et al., 2014). The ITS sequence of this Fomitopsis species (HM126455.1) shared 99% identity with those of Fomitopsis palustris (KJ995920.1) or F. ostreiformis (KC595918.1), but only 93.2% identity with that of F. meliae isolates identified in this study. Fomitopsis meliae can cause substantial pre-mature mortality of lemon trees and represents a major threat to the survival and profitability of lemon production in Arizona.
• Hu, J., & Wright, G. C. (2021). Canker and Wood Rot Pathogens in Southwest Arizona Lemon Orchards. Plant Pathology, 15. doi:https://doi.org/10.1111/ppa.13476
• Hu, J. (2020). Alfalfa mosaic virus (AMV) infections in garbanzo beans. University of Arizona Cooperative Extension Publication, 4. doi:https://extension.arizona.edu/pubs/alfalfa-mosaic-virus-amv-infections-garbanzo-beans
• Hu, J. (2020). Goss’s bacterial wilt and leaf blight of corn. University of Arizona Cooperative Extension Publication, 2. doi:https://extension.arizona.edu/pubs/goss%E2%80%99s-bacterial-wilt-leaf-blight-corn
• Hu, J. (2020). Phymatotrichopsis root rot of grape. University of Arizona Cooperative Extension Publication, 3. doi:https://extension.arizona.edu/pubs/phymatotrichopsis-root-rot-grape
• Hu, J. (2020). Phytophthora rots of apple and pistachio. University of Arizona Cooperative Extension Publication, 2. doi:https://extension.arizona.edu/pubs/phytophthora-rots-apple-pistachio
• Hu, J. (2020). Pierce’s disease of grape. University of Arizona Cooperative Extension Publication, 5. doi:https://extension.arizona.edu/pubs/pierce%E2%80%99s-disease-grape
• Hu, J. (2020). Pistachio foliar fungal diseases. University of Arizona Cooperative Extension Publication, 2. doi:https://extension.arizona.edu/pubs/pistachio-foliar-fungal-diseases
• Hu, J. (2020). Pistachio soilborne diseases. University of Arizona Cooperative Extension Publication, 4. doi:https://extension.arizona.edu/pubs/pistachio-soilborne-diseases
• Hu, J. (2020). Symptom identification of citrus brown wood rot (BWR). University of Arizona Cooperative Extension Publication, 4. doi:https://extension.arizona.edu/pubs/symptom-identification-citrus-brown-wood-rot
• Hu, J. (2020). Symptom identification of pecan Phymatotrichopsis Root Rot (PRR). University of Arizona Cooperative Extension Publication, 4. doi:https://extension.arizona.edu/pubs/symptom-identification-pecan-phymatotrichopsis-root-rot-prr
• Hu, J. (2021). Evaluation of nematicide products and their combinations for root-knot management in Arizona, 2020. Plant Disease Management Reports, 15(V029), 1. doi:10.1094/PDMR15
• Hu, J., & Norton, E. R. (2020). Alternaria leaf spot of cotton. University of Arizona Cooperative Extension Publication, 4. doi:https://extension.arizona.edu/pubs/alternaria-leaf-spot-cotton
• Hu, J., & Norton, E. R. (2020). Fusarium wilt of cotton. University of Arizona Cooperative Extension Publication, 4. doi:https://extension.arizona.edu/pubs/fusarium-wilt-cotton
• Hu, J., & Norton, E. R. (2020). Symptom identification and management of cotton seedling diseases. University of Arizona Cooperative Extension Publication, 4. doi:https://extension.arizona.edu/pubs/symptom-identification-management-cotton-seedling-diseases
• Hu, J., Masson, R., & Dickey, L. (2020). First Report of Beet Curly Top Virus Infecting Industrial Hemp (Cannabis sativa) in Arizona. Plant disease.
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  Industrial hemp (Cannabis sativa) is an emerging crop in Arizona, with many uses, including fiber, cosmetic products, and health food. In 2020, severe curly top disease outbreaks were observed in several hemp fields in Yuma and Graham Counties, Arizona, where disease incidence and severity were considerably high, up to 100% crop loss occurring in some fields. A wide range of symptoms have been observed at different infection stages and plant growth stages at the time of infection. Early stage symptoms manifest as light green-to-yellowing of new growth, similar to sulfur or micronutrient deficiency, usually combined with older leaves with dark green "blotchy" mosaic mottling overlaying light green chlorosis. Mosaic mottling of older leaves continues into mid-growth stage, and is coupled with more severe yellowing and witch's broom (stunted leaves and shortened internode length of stem) of apical meristematic tissue. Curling and twisting of new leaves has also been observed. Symptoms often appear to be isolated to individual branches, with other branches showing no visual symptoms, often outgrowing and covering affected branches until harvest. Late stage symptoms include severe leaf curling with or without twisting, continued stunting, and necrosis of yellow leaves, resulting in significant yield reduction. Severely affected plants dwarfed by the virus experienced high mortality rates later into the season, most likely attributed to reduced ability to overcome abiotic stress conditions. These symptoms indicated the likelihood of curly top caused by Beet curly top virus (BCTV), which has been recently reported in Colorado (Giladi et al., 2020). Shoots were collected from thirty-eight symptomatic and nine asymptomatic hemp plants from July to August, 2020. Leaves were also collected as positive control from four chili pepper plants with or without curly top symptoms in Cochise County. Genomic DNA was extracted using DNeasy Plant Pro Kit (Qiagen Inc., Valencia, CA) according to the manufacturer's instructions. BCTV-specific primers BCTV1 and BCTV2 were used to detect BCTV following a method by Rondon (Rondon et al., 2016). A 500 bp DNA fragment, indicative of BCTV, was amplified from all symptomatic hemp and chili pepper samples, but not from asymptomatic samples. Sequence analysis of this 500 bp DNA fragment revealed 98.99 % identity with GenBank accession MK803280, which is Beet curly top virus isolate from hemp identified in Western Colorado (Giladi et al., 2020). The full-length genomes of BCTV isolates from hemp and chili peppers were generated with additional primers 328F/945R (620bp), 455F/ 945R (490bp), OutR/ 2213F (1,190bp), 2609R/ 1278R (1,340bp), BCTV2/ 2609R (1,890bp) (Rondon et al., 2016, Strausbaugh et al., 2008). The complete nucleotide sequence (MW182244) from hemp was 2,929 bp and had 99.35% sequence identity with GenBank accession KX867055, which was a Worland strain of Beet curly top virus isolated from an Idaho sugar beet plant (Strausbaugh et al., 2017). Our hemp BCTV genome sequences shared 96.08% identity with the hemp strain of BCTV from Colorado (MK803280) and 99.50% identity with the BCTV isolate (MW188519) from chili pepper identified in this study. BCTV was reported on outdoor hemp in Western Colorado, in 2020 (Giladi et al., 2020). This is the first report of BCTV in Arizona causing curly top of industrial hemp in the field. In Arizona, BCTV is widespread on many agronomic crops including chili peppers and spread primarily by the phloem-feeding beet leafhoppers: Circulifer tenellus (Hemiptera: Cicadellidae) (Bennett, 1967). Due to the wide distribution of beet leafhoppers and abundant range of host plants for the virus, BCTV may become one of the most yield-limiting factors affecting the emerging industrial hemp production systems in Arizona.
• Hu, J. (2019). Evaluation of fungicide treatments on chile pepper for Phytophthora blight control in Arizona, 2018. Plant Disease Management Reports, 13(V129), 1.
• Hu, J. (2019). Evaluation of seed treatment products for increasing cotton stand and yield in Arizona, 2018. Plant Disease Management Reports, 13(CF046), 1. doi:10.1094/PDMR13
• Hu, J. (2019). First Report of Onion Bulb Rot Caused by Pantoea agglomerans in Arizona. Plant Disease, 103(6), 1408-1408. doi:10.1094/pdis-10-18-1749-pdn
• Hu, J. (2020). Evaluation of seed treatment products for increasing stand of direct-seeded guayule in Arizona, 2019. Plant Disease Management Reports, 14(ST001), 1. doi:10.1094/PDMR14
• Hu, J. (2020). Fungicide management of Septoria leaf spot of pistachio in Arizona, 2019. Plant Disease Management Reports, 14(PF007), 1. doi:10.1094/PDMR14
• Hu, J., & Norton, E. R. (2019). Evaluation of nematicide products and their combinations for root-knot management in Arizona, 2018. Plant Disease Management Reports, 14(N010), 1. doi:10.1094/PDMR13
• Hu, J., & Norton, E. R. (2020). Evaluation of nematicide products and their combinations for root-knot management in Arizona, 2019. Plant Disease Management Reports, 16(N001), 1. doi:10.1094/PDMR16
• Hu, J., & Norton, E. R. (2020). Evaluation of seed treatments and seeding rate for increasing cotton stand and yield in Arizona, 2019. Plant Disease Management Reports, 15(CF074), 1. doi:10.1094/PDMR15
• Hu, J., & Wright, G. C. (2019). Huanglongbing of Citrus. University of Arizona Cooperative Extension Publication, 7. doi:https://extension.arizona.edu/pubs/huanglongbing-citrus
• Hu, J. (2018). Cotton Stem Blight and Boll Rot. University of Arizona Cooperative Extension, 3. doi:https://extension.arizona.edu/pubs/cotton-stem-blight-boll-rot
• Hu, J. (2018). Evaluation of Syngenta foliar fungicide treatments on chile pepper for powdery mildew control in Arizona, 2017. Plant Disease Management Reports, 12(V129), 1. doi:10.1094/PDMR12
• Hu, J. (2018). Pecan Bacterial Leaf Scorch. University of Arizona Cooperative Extension Publication, 5. doi:https://extension.arizona.edu/pubs/pecan-bacterial-leaf-scorch
• Hu, J. (2018). Phymatotrichopsis Root Rot in Pecan. University of Arizona Cooperative Extension Publication, 5. doi:https://extension.arizona.edu/pubs/phymatotrichopsis-root-rot-pecan
• Hu, J. (2018). Vegetable Diseases Caused by Phytophthora capsici in Arizona. University of Arizona Cooperative Extension Publication, 8. doi:https://extension.arizona.edu/pubs/vegetable-diseases-caused-phytophthora-capsici-arizona
• Hu, J., & Kopec, D. M. (2018). Evaluation of fungicide treatments for bermudagrass decline control in Arizona, 2017. Plant Disease Management Reports, 12(T040), 1. doi:10.1094/PDMR12
• Hu, J., & Ottman, M. J. (2018). Stripe Rust of Small Grains. University of Arizona Cooperative Extension Publication, 4. doi:https://extension.arizona.edu/pubs/stripe-rust-small-grains
• Hu, J., Handique, U., & Norton, E. R. (2018). First Report of Sclerotinia Boll Rot and Stem Blight of Cotton in Arizona. Plant Disease, 102(8), 1. doi:https://doi.org/10.1094/PDIS-12-17-1897-PDN
• Wang, N., Jiang, J., & Hu, J. (2018). Control of Citrus Huanglongbing via Trunk Injection of Plant Defense Activators and Antibiotics.. Phytopathology, 108(2), 186-195. doi:10.1094/phyto-05-17-0175-r
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  Citrus huanglongbing (HLB) or greening is a devastating disease of citrus worldwide and no effective control measure is currently available. Plant defense activators environmentally friendly compounds capable of inducing resistance against many plant pathogens. Earlier studies showed that foliar spray of plant defense inducers could slow down HLB disease progress. In this study, eight plant defense activators and three antibiotics were evaluated in three field trials for their effect to control HLB by trunk injection of young and mature sweet orange trees. Results showed that four trunk injections of several activators, including salicylic acid, oxalic acid, acibenzolar-S-methyl, and potassium phosphate, provided significant control of HLB by suppressing 'Candidatus Liberibacter asiaticus' titer and disease progress. Trunk injection of penicillin, streptomycin, and oxytetracycline hydrochloride resulted in excellent control of HLB. In general, antibiotics were more effective in reduction of 'Ca. L. asiaticus' titer and HLB symptom expressions than plant defense activators. These treatments also resulted in increased yield and better fruit quality. Injection of both salicylic acid and acibenzolar-S-methyl led to significant induction of pathogenesis-related (PR) genes PR-1 and PR-2 genes. Meanwhile, injection of either potassium phosphate or oxalic acid resulted in significant induction of PR-2 or PR-15 gene expression, respectively. These results suggested that HLB diseased trees remained inducible for systemic acquired resistance under field conditions. In summary, this study presents information regarding controlling HLB via trunk injection of plant defense activators and antibiotics, which helps citrus growers in decision making regarding developing an effective HLB management program.
• Hu, J., & Wang, N. (2016). Evaluation of the Spatiotemporal Dynamics of Oxytetracycline and Its Control Effect Against Citrus Huanglongbing via Trunk Injection. Phytopathology, 106(12), 1495-1503.
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  Citrus huanglongbing (HLB) or greening is a devastating bacterial disease that has destroyed millions of trees and is associated with phloem-residing 'Candidatus Liberibacter asiaticus' (Las) in Florida. In this study, we evaluated the spatiotemporal dynamics of oxytetracycline in planta and its control effect against HLB via trunk injection. Las-infected 'Hamlin' sweet orange trees on 'Swingle' citrumelo rootstock at the early stage of decline were treated with oxytetracycline hydrochloride (OTC) using trunk injection with varying number of injection ports. Spatiotemporal distribution of OTC and dynamics of Las populations were monitored by high-performance liquid chromatography method and qPCR assay, respectively. Uniform distribution of OTC throughout tree canopies and root system was achieved 2 days postinjection. High levels of OTC (>850 µg/kg) were maintained in leaf and root for at least 1 month and moderate OTC (>500 µg/kg) persisted for more than 9 months. Reduction of Las populations in root system and leaves of OTC-treated trees were over 95% and 99% (i.e., 1.76 and 2.19 log reduction) between 2 and 28 days postinjection. Conditions of trees receiving OTC treatment were improved, fruit yield was increased, and juice acidity was lowered than water-injected control even though their differences were not statistically significant during the test period. Our study demonstrated that trunk injection of OTC could be used as an effective measure for integrated management of citrus HLB.
• Hu, J., Akula, N., & Wang, N. (2016). Development of a Microemulsion Formulation for Antimicrobial SecA Inhibitors. PloS one, 11(3), e0150433.
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  In our previous study, we have identified five antimicrobial small molecules via structure based design, which inhibit SecA of Candidatus Liberibacter asiaticus (Las). SecA is a critical protein translocase ATPase subunit and is involved in pre-protein translocation across and integration into the cellular membrane in bacteria. In this study, eleven compounds were identified using similarity search method based on the five lead SecA inhibitors identified previously. The identified SecA inhibitors have poor aqueous solubility. Thus a microemulsion master mix (MMX) was developed to address the solubility issue and for application of the antimicrobials. MMX consists of N-methyl-2-pyrrolidone and dimethyl sulfoxide as solvent and co-solvent, as well as polyoxyethylated castor oil, polyalkylene glycol, and polyoxyethylene tridecyl ether phosphate as surfactants. MMX has significantly improved the solubility of SecA inhibitors and has no or little phytotoxic effects at concentrations less than 5.0% (v/v). The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the SecA inhibitors and streptomycin against eight bacteria including Agrobacterium tumefaciens, Liberibacter crescens, Rhizobium etli, Bradyrhizobium japonicum, Mesorhizobium loti, and Sinorhizobium meliloti phylogenetically related to Las were determined using the broth microdilution method. MIC and MBC results showed that the 16 SecA inhibitors have antibacterial activities comparable to that of streptomycin. Overall, we have identified 11 potent SecA inhibitors using similarity search method. We have developed a microemulsion formulation for SecA inhibitors which improved the antimicrobial activities of SecA inhibitors.
• Hu, J., Telenko, D., Phipps, P. M., & Grabau, E. A. (2016). Comparative susceptibility of peanut genetically engineered for sclerotinia blight resistance to non-target peanut pathogens. EUROPEAN JOURNAL OF PLANT PATHOLOGY, 145(1), 177-187.
• Telenko, D. E., Phipps, P. M., Hu, J., Hills, H., & Grabau, E. A. (2015). Quantifying transgene flow rate in transgenic Sclerotinia-resistant peanut lines. Field Crops Research, 178, 69-76. doi:10.1016/j.fcr.2015.03.016
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  Abstract Multi-year transgenic field trials were conducted to assess the extent of pollen-mediated transgenic flow in Virginia to support a petition requesting deregulated status for Blight Blocker peanuts from USDA Animal and Plant Health Inspection Service (APHIS) Biotechnology Regulatory Services (BRS). We measured transgene flow from transgenic lines to their non-transgenic parental cultivars. A colorimetric method based on quantification of hydrogen peroxide released from oxalic acid in the presence of the oxalate oxidase was used to screen seed embryos from non-transgenic rows at various distances from the transgenic source. The overall transgene flow rate in three cultivars was 0.2094% based on screening over 85,000 seeds. In general, the transgene flow rate greatly declined past 10 m from the transgene source. However, a transgene flow rate of less than 0.05% did occur sporadically at greater distances than 10 m. In conclusion, transgene flow in peanut can be spatially confined to provide negligible rates using relatively short separation distances. The extremely low rate of transgene flow at greater distance was dependent on ecological and environmental contexts, particularly on foraging patterns and flight distance of pollinators.
• Cevallos-Cevallos, J. M., Gu, G., Richardson, S. M., Hu, J., & van Bruggen, A. H. (2014). Survival of Salmonella enterica Typhimurium in water amended with manure. Journal of food protection, 77(12), 2035-42.
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  Outbreaks of Salmonella enterica have been associated with water sources. Survival of S. enterica in various environments has been studied but survival in water has rarely been attempted. In two separate experiments, we examined the survival of S. enterica Typhimurium in clean spring water at various eutrophication levels and temperatures. In the first experiment, lasting for 135 days, survival of S. enterica (10(10) CFU/ml) in water with 0, 50, 100, 500, and 1,000 mg/liter of added carbon at 7, 17, and 27°C was monitored weekly. In the second experiment, lasting for 3 weeks, survival of S. enterica in water at 0, 100, and 200 mg/ liter of added carbon and 27°C was studied daily. Each experiment had four replicates. Dissolved organic carbon was measured daily in each experiment. At the beginning, midpoint, and end of the survival study, microbial communities in both experiments were assessed by denaturing gradient gel electrophoresis (DGGE). Even at minimal carbon concentrations, S. enterica survived for at least 63 d. Survival of Salmonella was highly dependent on eutrophication levels (as measured by dissolved organic carbon) and temperature, increasing at high eutrophication levels, but decreasing at high temperatures. Survival was also strongly affected by microbial competition or predation.
• Hu, J., Johnson, E. G., Wang, N. Y., Davoglio, T., & Dewdney, M. M. (2014). qPCR Quantification of Pathogenic Guignardia citricarpa and Nonpathogenic G. mangiferae in Citrus. Plant disease, 98(1), 112-120.
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  Citrus black spot, a major citrus disease caused by Guignardia citricarpa, was recently introduced in Florida. The nonpathogenic fungal endophyte G. mangiferae is commonly found in the same citrus tissues as G. citricarpa. Quantitative polymerase chain reaction (qPCR) assays based on internal transcribed spacer (ITS)-1 genes were developed to detect, quantify, and distinguish between these morphologically similar organisms in environmental samples. The primer/probe sets GCITS and GMITS were more than 95% efficient in single-set reactions in complex environmental DNA samples. Detection of 10 fg of G. citricarpa and G. mangiferae DNA was possible. Pycnidiospore disruption resulted in detection of single pycnidiospores with 78 (59 to 102; 95% confidence interval [CI]) and 112 (92 to 136; 95% CI) ITS copies for G. citricarpa and G. mangiferae, respectively. Detection was from partially decomposed leaves where fruiting bodies cannot be morphologically distinguished. Temperature and wetting period have significant effects on Guignardia spp. pseudothecia production in leaf litter. Based on relative biomass or the proportion of nuclei detected, G. citricarpa and G. mangiferae respond more strongly to wetting period than temperature. This qPCR assay will provide additional epidemiological data on black spot in tissues where G. citricarpa and G. mangiferae are not easily distinguished.
• Hu, J., Telenko, D. E., Phipps, P. M., & Grabau, E. A. (2014). Assessment of peanut quality and compositional characteristics among transgenic sclerotinia blight-resistant and non-transgenic susceptible cultivars. Journal of agricultural and food chemistry, 62(31), 7877-85.
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  This study presents the results of a comparison that includes an analysis of variance and a canonical discriminant analysis to determine compositional equivalence and similarity between transgenic, sclerotinia blight-resistant and non-transgenic, susceptible cultivars of peanut in 3 years of field trials. Three Virginia-type cultivars (NC 7, Wilson, and Perry) and their corresponding transgenic lines (N70, W73, and P39) with a barley oxalate oxidase gene were analyzed for differences in key mineral nutrients, fatty acid components, hay constituents, and grade characteristics. Results from both analyses demonstrated that transgenic lines were compositionally similar to their non-transgenic parent cultivar in all factors as well as market-grade characteristics and nutritional value. Transgenic lines expressing oxalate oxidase for resistance to sclerotinia blight were substantially equivalent to their non-transgenic parent cultivar in quality and compositional characteristics.
• Li, Y., & Hu, J. (2014). Inheritance of mefenoxam resistance in Phytophthora nicotianae populations from a plant nursery. European Journal of Plant Pathology, 139(3), 545-555. doi:10.1007/s10658-014-0410-0
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  Three sexual crosses involving isolates of P. nicotianae with differing sensitivity to mefenoxam were established to study the inheritance of mefenoxam resistance. Mefenoxam sensitivity was determined by measuring the mycelial growth on both mefenoxam-amended clarified V8 agar and non-amended agar and then calculating the relative growth. When both parents had the same phenotype (both were resistant or both were sensitive), all F 1 progeny had the parental phenotype and no segregation for a major effect gene was observed in sensitivity to mefenoxam. However, variations in the mycelial growth of progeny indicated the segregation of minor-effect genes. When the cross involving the mefenoxam-resistant isolate 3A4 and a sensitive parent, the F 1 progeny segregated for mefenoxam resistance in a ratio of 1:1 (resistant: sensitive), indicating that the mefenoxam resistance is controled by a single dominant gene. Mating type was not linked to the mefenoxam-resistance gene locus. One RAPD marker linked in trans to the MEX locus was obtained by bulked segregant analysis using RAPD markers and was converted to a sequence characterized amplified region marker (SCAR). The SCAR maker identified in this study is a limited but useful tool for differentiating homozygous resistant isolates from sensitive isolates of P. nicotianae.
• Gu, G., Hu, J., Cevallos-Cevallos, J. M., Richardson, S. M., Bartz, J. A., & van Bruggen, A. H. (2011). Internal colonization of Salmonella enterica serovar Typhimurium in tomato plants. PloS one, 6(11), e27340.
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  Several Salmonella enterica outbreaks have been traced back to contaminated tomatoes. In this study, the internalization of S. enterica Typhimurium via tomato leaves was investigated as affected by surfactants and bacterial rdar morphotype, which was reported to be important for the environmental persistence and attachment of Salmonella to plants. Surfactants, especially Silwet L-77, promoted ingress and survival of S. enterica Typhimurium in tomato leaves. In each of two experiments, 84 tomato plants were inoculated two to four times before fruiting with GFP-labeled S. enterica Typhimurium strain MAE110 (with rdar morphotype) or MAE119 (without rdar). For each inoculation, single leaflets were dipped in 10(9) CFU/ml Salmonella suspension with Silwet L-77. Inoculated and adjacent leaflets were tested for Salmonella survival for 3 weeks after each inoculation. The surface and pulp of ripe fruits produced on these plants were also examined for Salmonella. Populations of both Salmonella strains in inoculated leaflets decreased during 2 weeks after inoculation but remained unchanged (at about 10(4) CFU/g) in week 3. Populations of MAE110 were significantly higher (P
• Ross, D. S., Richardson, P. A., Moorman, G. W., Lea-cox, J. D., Kong, P., Hu, J., Hong, C., & Ghimire, S. R. (2011). Distribution and Diversity of Phytophthora species in Nursery Irrigation Reservoir Adopting Water Recycling System During Winter Months. Journal of Phytopathology, 159(11-12), 713-719. doi:10.1111/j.1439-0434.2011.01831.x
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  Irrigation water recycling is an increasingly important practice in agriculture in the context of diminishing water supply and the regulatory requirements in some parts of the world. This practice potentially accumulates and disseminates plant pathogens including Phytophthora species that pose a great threat to agriculture and forest ecosystems. Despite a high economic importance of Phytophthora species, the current understanding of their aquatic ecology is very limited. Therefore, a study was conducted to investigate the distribution and diversity of Phytophthora species in an irrigation reservoir of a commercial nursery in eastern Virginia over two consecutive winters. Multiple baits were deployed in surface water at a run-off entrance, 20, 40, 60 and 80 m from the entrance and near the pump inlet and at various depths at the 20-m station. Ten different Phytophthora species were detected in this study that included P. citrophthora, P. gonapodyides, P. hydropathica, P. inundata, P. irrigata, P. megasperma, P. pini, P. polonica, P. syringae and P. tropicalis. Phytophthora recovery declined through the winters from November to March. It also declined with distance from the run-off entrance. These results suggest that water decontamination during winter irrigation events is required at this nursery and possibly in the nurseries from the southern part of the United States. The placement of the pump inlet away from run-off entrance may be a viable strategy to reduce the crop health risk.
• Shew, B. B., Phipps, P. M., Partridge-telenko, D. E., Livingstone, D. M., Hu, J., & Grabau, E. A. (2011). Sclerotinia blight resistance in Virginia-type peanut transformed with a barley oxalate oxidase gene.. Phytopathology, 101(7), 786-93. doi:10.1094/phyto-10-10-0266
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  Transgenic peanut lines expressing oxalate oxidase, a novel enzyme to peanut, were evaluated for resistance to Sclerotinia blight in naturally infested fields over a 5-year period. Area under the disease progress curve (AUDPC) for transgenic lines in single rows planted with seed from single-plant selections averaged 78, 83, and 90% lower than nontransgenic parents in 2004, 2005, and 2006, respectively. In addition, AUDPC in 14 transgenic lines planted with bulked seed in two-row plots averaged 81% lower compared with nontransgenic parents in 2005 and 86% lower in 16 transgenic lines in 2006. Six transgenic lines yielded 488 to 1,260 kg/ha greater than nontransgenic parents in 2005, and 10 lines yielded 537 to 2,490 kg/ha greater in 2006. Fluazinam (0.58 kg a.i./ha) fungicide sprays in 2008 and 2009 reduced AUDPC in transgenic and nontransgenic lines but AUDPC was lowest in transgenic lines. Without fluazinam, yields of transgenic lines averaged 1,133 to 1,578 kg/ha greater than nontransgenic lines in 2008 and 1,670 to 2,755 kg/ha greater in 2009. These results demonstrated that the insertion of barley oxalate oxidase in peanut conveyed a high level of resistance to Sclerotinia blight, and negated the need for costly fungicide sprays.
• Hu, J., Hong, C., Stromberg, E. L., & Moorman, G. W. (2010). Mefenoxam Sensitivity in Phytophthora cinnamomi Isolates. Plant disease, 94(1), 39-44.
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  Phytophthora cinnamomi is a destructive root pathogen of numerous woody plant species in the ornamental plant nursery. Sixty-five isolates of P. cinnamomi were evaluated for mefenoxam sensitivity on 20% clarified V8 agar amended with mefenoxam at 0 or 100 μg/ml. In the presence of mefenoxam at 100 μg/ml, eight isolates were intermediately sensitive, with mycelium growth ranging between 11 and 18% of the nonamended control, and 57 isolates were highly sensitive, with little or no mycelium growth. Five intermediately sensitive and five sensitive isolates were chosen to characterize their responses to mefenoxam at 0, 0.1, 1, 10, and 100 μg/ml. For intermediately sensitive isolates, the mefenoxam concentration causing 50% inhibition of mycelium growth (EC values) ranged between 0.03 and 0.08 μg/ml; EC values for sensitive isolates varied from 0.01 to 0.02 μg/ml. Five intermediately sensitive and seven sensitive isolates were selected further to assess in vivo sensitivity to mefenoxam using Lupinus angustifolius 'Russell Hybrids'. Lupine seedlings were treated with distilled water or mefenoxam at label rate (Subdue MAXX, 1 fl. oz. of product per 100 gal.) and then, 2 days later, inoculated with a 5-mm-diameter mycelial plug of P. cinnamomi on each cotyledon. Mefenoxam-treated plants averaged more than 96% less disease than water-treated plants. Mefenoxam provided adequate protection of lupines from infection by all 12 isolates regardless of their in vitro levels of sensitivity to mefenoxam. The ability to develop mefenoxam resistance was assessed in P. cinnamomi isolates with different mefenoxam sensitivity by UV mutagenesis and adapting mycelium to increasing concentrations of mefenoxam. Both UV mutagenesis and mycelium adaptation generated isolates with reduced sensitivity to mefenoxam. These isolates, however, did not grow as quickly as their corresponding parent. This study suggests that P. cinnamomi populations from ornamental nurseries in Virginia are sensitive to mefenoxam.
• Phipps, P. M., Hu, J., & Eisenback, J. D. (2009). Cost and Benefit of Seed Treatments and Temik 15G in Furrow for Seedling Disease and Nematode Control in Virginia, 2008. Plant Disease Management Report.
• Stromberg, E. L., Moorman, G. W., Hu, J. H., & Hong, C. X. (2008). Mefenoxam sensitivity and fitness analysis of Phytophthora nicotianae isolates from nurseries in Virginia, USA. Plant Pathology, 57(4), 728-736. doi:10.1111/j.1365-3059.2008.01831.x
  More info

  Mefenoxam is one of the most commonly used fungicides for managing diseases caused by Phytophthora spp. on ornamentals. The objectives of this study were to determine whether Phytophthora nicotianae, a destructive pathogen of numerous herbaceous annual and perennial plant species in nurseries, has developed resistance to mefenoxam, and to evaluate the fitness of mefenoxam-resistant isolates. Ninety-five isolates of P. nicotianae were screened for sensitivity to mefenoxam on 20% clarified V8 agar at 100 a.i. µg mL−1. Twenty-five isolates were highly resistant to this compound with EC50 values ranging from 235·2 to 466·3 µg mL−1 and four were intermediately resistant with EC50 values ranging from 1·6 to 2·9 µg mL−1. Sixty-six isolates were sensitive with EC50 values less than 0·04 µg mL−1. Nine resistant and seven sensitive isolates were tested for mefenoxam sensitivity on Pelargonium × hortorum cv. White Orbit. Mefenoxam provided good protection of pelargonium seedlings from colonization by sensitive isolates, but not by any resistant isolates. Four resistant and four sensitive isolates were compared for fitness components and their relative competitive ability on Lupinus Russell Hybrids in the absence of mefenoxam. Resistant isolates outcompeted sensitive ones within 3 to 6 sporulation cycles on lupin seedlings, regardless of their initial proportions in mixed zoospore inoculum. Resistant isolates exhibited greater infection rate and higher sporulation ability than sensitive ones when they were applied separately onto lupins. These results suggest that fungicide resistance may pose a serious challenge to the continued effectiveness of mefenoxam as a control option for nursery growers.
• Hu, J., Hong, C., Stromberg, E. L., & Moorman, G. W. (2007). Effects of Propamocarb Hydrochloride on Mycelial Growth, Sporulation, and Infection by Phytophthora nicotianae Isolates from Virginia Nurseries. Plant disease, 91(4), 414-420.
  More info

  Propamocarb hydrochloride is a systemic fungicide commonly used for control of Phytophthora diseases of nursery crops. Here we report on the effect of this compound on different growth stages of Phytophthora nicotianae, a major pathogen of numerous herbaceous and some woody ornamental plants. A total of 71 isolates were assayed for sensitivity to propamocarb at two concentrations of 1.8 mg/ml (label rate) and 10 mg/ml using clarified V8 agar as a base medium. All isolates grew at 10 mg/ml with the most sensitive isolate having 34.8% relative growth compared with growth on nonamended medium. Nine isolates were selected and further tested for mycelial growth at 0, 1, 10, 25, 50, and 100 mg/ml, and for sporangium production, zoospore motility, and germination at 0, 5, 50, 500, 5,000, and 50,000 μg/ml. EC values ranged from 2.2 to 90.1 mg/ml for mycelial growth, 133.8 to 481.3 μg/ml for sporangium production, 88.1 to 249.8 μg/ml for zoospore motility, and 1.9 to 184.6 μg/ml for zoospore germination, respectively. In addition, 17 selected isolates were evaluated for propamocarb sensitivity on Pelargonium × hortorum cv. White Orbit. Two days after seedlings were treated with propamocarb at 3.6 mg/ml, they were inoculated by either inverting one 5-mm-diameter plug of a 3-day-old culture or applying a 10-μl drop containing 20 zoospores onto each cotyledon. Propamocarb hydrochloride provided good protection of geranium seedlings from zoospore infections but not from mycelial infections. These results suggest that this fungicide must be used preventively for Phytophthora disease management and that mycelial growth may not be the most reliable measurement to determine the development of fungicide resistance to this compound in Phytophthora species at production facilities and in the landscape.

Proceedings Publications

• Hu, J. (2019, Jan/Spring). Fusarium species and Fusarium wilt pathogens associated with roots of cottons in Arizona. In The Beltwide Cotton Conference.

Presentations

• Hu, J. (2024, December/Winter). Crop Disease Update for 2023 Growing Season . Field Crops Clinics. Buckeye, AZ,.
• Hu, J., & Norton, E. R. (2024, Jan/Spring). 2023 Nematode Research Trial Results for Managing Cotton Root-knot Nematode. The Beltwide Cotton Conference/ Nematode Research Committee. Fort Worth, TX, USA.
• Hu, J., & Norton, E. R. (2024, Jan/Spring). 2023 Seed Treatment Trial Results for Cotton Seedling Diseases. The Beltwide Cotton Conference/ National Cotton Disease Council Seed Treatment Committee. Fort Worth, TX, USA: Cotton Incorporated.
• Hu, J. (2023, April/Spring). IR4 project update for Arizona. 2023 Western Region SLR/CLC Meeting. Davis, CA.
• Hu, J. (2023, August/Summer). Update on Plant Disease Diagnostics in Arizona. The Annual Meeting of the Western Plant Diagnostic Network. Denver, CO: WPDN.
• Hu, J. (2023, December/Winter). Identification and Management of Emerging Grapevine Diseases. Arizona Winter Viticulture Symposium. Tucson, AZ.
• Hu, J. (2023, January/Spring). Common diseases and disorders of citrus. Citrus Clinic in Mesa. Mesa, Arizona: Maricopa County Master Gardener.
• Hu, J. (2023, January/Spring).

  Arizona Crop Disease Update: Overview of the 2022 Growing Season

  . The 90th Annual Board Meeting, Arizona Crop Improvement Association. Sedona, Arizona: Maricopa County Master Gardener.
• Hu, J. (2023, January/Spring). Citrus Diseases and Disorders in Arizona. Virtual Citrus Clinic Workshop. Mesa, Arizona: Maricopa County Master Gardener.
• Hu, J. (2023, May/summer). 2022 Crop Diseases Update. La Paz County Crop Update Meeting. Parker, Arizona.
• Hu, J. (2023, May/summer). Urban Landscape Tree Diseases in Arizona Low Desert. The 32th Annual Desert Horticulture Conference. Tucson, Arizona.
• Hu, J. (2023, September/Fall). Common Tree Diseases: How to Identify Them and Protect Urban Forest. The Annual Conference & Workshop, Arizona Community Tree Council. Camp Verde, Arizona.
• Hu, J. (2023, September/Fall). Diseases of ornamentals; Arizona Plant Diagnostic Network. Plant Pest and Disease Seminar. Tucson, AZ.
• Hu, J., & Norton, E. R. (2023, Jan/Spring). 2022 Nematode Research Trial Results for Managing Cotton Root-knot Nematode. The Beltwide Cotton Conference/ Nematode Research Committee. New Orleans, LS USA.
• Hu, J., & Norton, E. R. (2023, Jan/Spring). 2022 Seed Treatment Trial Results for Cotton Seedling Diseases. The Beltwide Cotton Conference/ National Cotton Disease Council Seed Treatment Committee. New Orleans, LS USA: Cotton Incorporated.
• Hu, J. (2022, April/Spring). Updates on Emerging Plant Diseases in Arizona. The 2022 National Plant Diagnostic Network Meeting: Propelling diagnostics into the future. University of California, Davis: The National Plant Diagnostic Network.
• Hu, J. (2022, December/Winter). Lemon canker and wood rot disease update. Desert Southwest Citrus and Date Workshops in Phoenix. Phoenix, Arizona.
• Hu, J. (2022, December/Winter). Lemon canker and wood rot disease update. Desert Southwest Citrus and Date Workshops in Yuma. Yuma, Arizona.
• Hu, J. (2022, February/Spring). Disease Update on Grapevines and Nut Trees. Southeastern Arizona Farm and Ranch Trade Show. Willcox, Arizona.
• Hu, J. (2022, Feburary/Spring). Summary of the 2021 Cotton Disease Situation. Arizona Cotton Symposium. Casa Grande, Pinal County: Pinal Cooperative Extension.
• Hu, J. (2022, January/Spring). Citrus Diseases 101 in Arizona. Citrus Clinic in Mesa. Mesa, Arizona: Maricopa County Master Gardener.
• Hu, J. (2022, January/Spring). Citrus Diseases 101 in Arizona. Citrus Clinic in Surprise. Mesa, Arizona: Maricopa County Master Gardener.
• Hu, J. (2022, January/Spring). Citrus Diseases and Disorders in Arizona. Virtual Citrus Clinic Workshop. Mesa, Arizona: Maricopa County Master Gardener.
• Hu, J. (2022, July/Summer). How to identify and manage diseases of your crops. Summer field crops workshop in Bonita. Bonita, Graham County.
• Hu, J. (2022, July/Summer). Identification and management of cotton diseases. Cotton IPM Workshop. Maricopa Ag Center.
• Hu, J. (2022, July/Summer). Identification and management of cotton diseases. Cotton “Tent Talks”, A Tumbling T Ranches. Goodyear, Arizona.
• Hu, J. (2022, July/Summer). Identification and management of cotton diseases. Summer field crops workshop in Thatcher. Thatcher, Graham County.
• Hu, J. (2022, March/Spring). Diagnosis and management of Phymatotrichopsis root rot in pecan. The Western Pecan Growers Conference. Las Cruces, NM: The Western Pecan Growers Association.
• Hu, J. (2022, November). Guayule disease identification and management. Guayule Field Day, Bridgestone America. Eloy AZ: Pinal Cooperative Extension.
• Norton, E. R. (2022, Jan/Spring). Effects of Heat Stress on Cotton Production in the Low Deserts of Arizona. The Beltwide Cotton Conference. San Antonio, TX, USA: National Cotton Council.
• Hu, J. (2021, April). Extension Plant Pathology. PLP 550. Virtual class: Dr. Arnold's class.
• Hu, J. (2021, April). Tree and landscape disease and disorders Identification and Management. The 4th Arizona School IPM Conference. Maricopa AZ: Maricopa Cooperative Extension.
• Hu, J. (2021, August). Research Updates on Pecan diseases in Arizona. The 2021 Annual Meeting of Arizona Pecan Growers Association. Tucson, Arizona: Arizona Pecan Growers Association.
• Hu, J. (2021, December/Winter). Alfalfa and Forage Crops Disease Updates for the Low Dessert. La Paz County Crop Update Meeting. Parker, Arizona.
• Hu, J. (2021, December/Winter). Lemon canker and wood rot disease in the southwest. Desert Southwest Citrus and Date Seminar. Yuma, Arizona.
• Hu, J. (2021, February). Cotton Disease Identification and Management. The 2021 Arizona Cotton Production Update Meeting. Safford AZ: Safford Ag Station, Graham Cooperative Extension.
• Hu, J. (2021, February). Cotton and Alfalfa Diseases Identification and Management. Southwest Ag Summit. Yuma AZ: Yuma Fresh Vegetable Association.
• Hu, J. (2021, January). Cotton Disease Identification and Management. The 2021 UArizona Cooperative Extension Field Crops “Clinics”. Maricopa AZ: Maricopa Cooperative Extension.
• Hu, J. (2021, January). Plant Pathology and Major Plant Diseases of Citrus in Arizona. The 19th Citrus Clinic, Maricopa Master Gardener Program. Phoenix AZ: Maricopa Cooperative Extension.
• Hu, J. (2021, July). Witches’ broom on landscape trees. Pima County Master Gardener Training Program. Tucson AZ: Pima Cooperative Extension.
• Hu, J. (2021, July/Summer). Fusarium wilt of cotton. Cotton “Tent Talks”, A Tumbling T Ranches. Goodyear, Arizona.
• Hu, J. (2021, May). Diagnosing Common Disorders of Trees and Shrubs in Arizona Landscapes. The 30th Annual Desert Horticulture Conference. Tucson, Arizona.
• Hu, J. (2021, November/Fall). Introduction to Plant Pathology. Pima County Master Gardener Training Program. Tucson, Arizona.
• Hu, J. (2021, October). Guayule Diseases. Guayule Field Day, Bridgestone America. Eloy AZ: Pinal Cooperative Extension.
• Hu, J. (2021, October). Phytophthora Disease Management. The 2021 UArizona Urban Ag/Beginner Farmer Seminar. Phoenix AZ: Maricopa Cooperative Extension.
• Hu, J. (2020, August). Diagnosing Pecan Diseases in Arizona. The 2020 Annual Meeting of Arizona Pecan Growers Association. Tucson, Arizona.
• Hu, J. (2020, August/Summer). Industrial Hemp Diseases. Virtual "Tent Talks". Tucson, Arizona: Maricopa Cooperative Extension.
• Hu, J. (2020, February/Spring). Common diseases and Management on Nut Trees. Southeastern Arizona Farm and Ranch Trade Show. Willcox, Arizona.
• Hu, J. (2020, February/Spring). Fusarium Wilt of Cotton and Cotton Seedling Diseases. Farm Home Ranch Day. Safford, Arizona.
• Hu, J. (2020, January). Seed Treatments for Cotton Seedling Diseases and Root-Knot Nematodes. The Beltwide Cotton Conference. Austin TX USA: Beltwide Disease Research and Education Committee.
• Hu, J. (2020, January/Spring). Diagnosis and Management of Citrus Diseases in Arizona. Citrus Clinic in Mesa. Mesa, Arizona: Maricopa County Master Gardener.
• Hu, J. (2020, January/Spring). Diagnosis and management of citrus diseases for homeowners. Citrus Clinic in Surprise. Surprise, Arizona: Maricopa County Master Gardener.
• Hu, J. (2020, January/Spring). Early Detection and Management of Cotton Seedling Diseases. Field Crop "Clinics". Buckeye, Arizona: Maricopa County Cooperative Extension.
• Hu, J. (2020, March). Update on Plant Disease Diagnostics in Arizona. The 2020 Regional Meeting of Western Plant Diagnostic Network. Tucson, Arizona.
• Hu, J. (2020, March/Spring). Identification and management strategies for Cotton Seedling Diseases and Alfalfa diseases. La Paz County Crop Update Meeting. Parker, Arizona.
• Hu, J. (2020, May). Common Landscape Plant Problems in Southern Arizona. The 29th Annual Desert Horticulture Conference. Tucson, Arizona.
• Hu, J. (2020, November/Fall). Introduction to Plant Pathology. Pima County Master Gardener Training Program. Tucson, Arizona.
• Hu, J. (2020, September). Verticillium wilt and Fusarium wilt Management of cotton. The 10th Annual Central Arizona Farmer Field day. Casa Grande, Arizona.
• Hu, J. (2019, January/Spring). Diagnosis and Management of Citrus Diseases in Arizona. Citrus Clinic in Mesa. Mesa, Arizona: Maricopa County Master Gardener.
• Hu, J. (2019, January/Spring). Diagnosis and management of citrus diseases for homeowners. Citrus Clinic in Surprise. Surprise, Arizona: Maricopa County Master Gardener.
• Hu, J. (2019, January/Spring). Disease Update for Field Crops. Buckeye Field Crops Clinic. Buckeye, Arizona.
• Hu, J. (2019, January/Spring). Disease Update for Field Crops. Winter Field Crop Meetings. Casa Grande, Arizona.
• Hu, J. (2019, January/Spring). Field Performance of Seed- and Soil-applied chemicals against cotton seedling diseases. The Beltwide Cotton Conference. New Orleans LA USA: Beltwide Disease Research and Education Committee.
• Hu, J. (2019, January/Spring). Research Updates in Citrus Brown Wood Rot and HLB. Brown Wood Rot Seminar. Yuma, Arizona.
• Hu, J. (2019, January/Spring). Tree Disease Update for Master Gardeners. Master Gardener Planning and Coordination Meeting. Phoenix, Arizona.
• Hu, J. (2019, July/Summer). Soil Testing for Cotton Root Rot and Fusarium Wilt. Cotton “Tent Talks”, A Tumbling T Ranches. Goodyear, Arizona.
• Hu, J. (2019, March/Spring). Fusarium Wilt of Cotton and Alfalfa Diseases. La Paz County Crop Update Meeting. Parker, Arizona.
• Hu, J. (2019, May). Disease Issues in Arizona Pecans. The 2019 Annual Meeting of Arizona Pecan Growers Association. Tucson, Arizona.
• Hu, J. (2019, May). Major Diseases of Citrus in Arizona. The 28th Annual Desert Horticulture Conference. Tucson, Arizona.
• Hu, J. (2019, November/Winter). Citrus Diseases and Management Strategies. Central Arizona Citrus Seminar. Maricopa Cooperative Extension Office, Phoenix, Arizona.
• Hu, J. (2019, November/Winter). Research Update on Citrus Brown Wood Rot. Western Arizona Citrus Seminar. Yuma, Arizona.
• Hu, J. (2018, April). Crop Diseases in Arizona. PLS 339. Virtual class: Dr. Quist's class.
• Hu, J. (2018, April). Extension Plant Pathology. PLP 550. Virtual class: Dr. Arnold's class.
• Hu, J. (2018, April/Spring). Introduction to Plant Pathology. Garden & Landscape Short Course by Pinal County Master Gardener Training Program. Apache Junction, Arizona: Pinal County Extension Office.
• Hu, J. (2018, February/Spring). Management and Prevention of Fusarium Race 4 and Other Cotton Diseases. Farm Home Ranch Day. Safford, Arizona.
• Hu, J. (2018, Jan/Spring). Field Performance of Seed- and Soil-applied chemicals against cotton seedling diseases. The Beltwide Cotton Conference. San Antonio, TX: Beltwide Disease Research and Education Committee.
• Hu, J. (2018, January/Spring). Epidemiology and management of seedling diseases and Fusarium wilt on Cotton. Winter Field Crops Clinics with Dow DuPont. Marana, Arizona.
• Hu, J. (2018, January/Spring). Epidemiology and management of seedling diseases and Fusarium wilt on Cotton. Winter Field Crops Meeting. Casa Grande, Arizona.
• Hu, J. (2018, January/Spring). Regional exotic disease update & sharping observation skills in diagnosis. Sentinel Plant Network Workshop, NPDN &SPN. Tucson, Arizona.
• Hu, J. (2018, June). Epidemiology and Management of Cotton Seedling Diseases. The Annual Board Meeting of Arizona Crop Improvement Association. Sedona, Arizona: Arizona Crop Improvement Association.
• Hu, J. (2018, March/Spring). Step-by-Step Guide to Vineyard Diagnostics. Arizona Grape Growers Symposium. Benson, Arizona.
• Hu, J. (2018, May). Arizona Tree Disease Update. The Shade Conference. Phoenix, Arizona: Arizona Nursery Association.
• Hu, J. (2018, May). Common Diseases and Their Management of Urban Trees. Turfgrass Field Day. Tucson, Arizona.
• Hu, J. (2018, May). Recognizing and Managing Diseases on Landscape Plants. The 27th Annual Desert Horticulture Conference. Tucson, Arizona.
• Hu, J. (2019, June/Summer). Fusarium Wilt of Cotton Update. Cotton “Tent Talks” Meeting. Yuma Ag Center, Yuma, Arizona.
• Hu, J. (2017, December/Winter). Leaf scorch of shade trees and other ornamentals & potential new disease threats to urban forests and communities. Pest Management and Pesticide Safety Seminar in Phoenix. Phoenix, Arizona.
• Hu, J. (2017, February/Spring). Controlling Diseases of Fruit and Nut Trees and Grapes. Farm Home Ranch Day. Safford, Arizona.
• Hu, J. (2017, February/Spring). Controlling Diseases of Fruit and Nut Trees and Grapes. The 38th Annual Southeastern Arizona Ag Day & Trade Show. Willcox, Arizona.
• Hu, J. (2017, January/Spring). Building a Successful Extension Plant Pathology Program. Master Gardener Planning and Coordination Meeting. Phoenix, Arizona.
• Hu, J. (2017, January/Spring). Extension Plant Pathology Program Update. Buckeye Field Crops Clinic. Buckeye, Arizona.
• Hu, J. (2017, July). Citrus Tree Disease Management. Tree Pest Management Workshop, Arizona Community Tree Council. Phoenix, Arizona.
• Hu, J. (2017, July). Shot Hole Borer-Fusarium Dieback and Xylella Leaf Scorch. The Annual Conference & Workshop, Arizona Community Tree Council. Prescott, Arizona.
• Hu, J. (2017, May). Bacterial Leaf Scorch by Xylella fastidiosa. The Shade Conference. Phoenix, Arizona: Arizona Nursery Association.
• Hu, J. (2017, May). Citrus Greening Disease. Tree Health Care Workshop. Phoenix, Arizona: Arizona Nursery Association.
• Hu, J. (2017, May). Controlling Diseases of Fruit and Nut Trees and Grapes. The 26th Annual Desert Horticulture Conference. Tucson, Arizona.
• Hu, J. (2017, May). Leaf scorch of shade trees and other ornamentals & potential new disease threats to urban forests and communities. Pest Management and Pesticide Safety Seminar in Scottsdale. Scottsdale, Arizona.
• Hu, J. (2017, May). Leaf scorch of shade trees and other ornamentals & potential new disease threats to urban forests and communities. Pest Management and Pesticide Safety Seminar in Sun City West. Sun City West, Arizona.
• Hu, J. (2018, January/Spring). Extension Plant Pathology Program Update. Winter Field Crops Clinics with Dow DuPont. Marana, Arizona.
• Hu, J. (2016, May). Citrus Greening – High Alert but Not Present in AZ. Tree Health Care Workshop. Tucson, Arizona.
• Hu, J. (2016, May). Extension Plant Pathology Program at UA. The Southern Arizona Arborist Group Meeting. Phoenix, Arizona: Arizona Nursery Association.
• Hu, J. (2016, May). How to Recognize Plant Diseases. Pest Management and Pesticide Safety Seminar in Paradise. Paradise, Arizona.
• Hu, J. (2016, May). How to Recognize Plant Diseases. Pest Management and Pesticide Safety Seminar in Sun City West. Sun City West, Arizona.

Poster Presentations

• Hu, J., Norton, E. R., Hagan, A., Faske, T. R., Hutmacher, R. B., Miller, J., Small, I., Grabau, Z., Kemerait, R. C., Price, P., Allen, T. W., Atwell, S., Idowu, J., Thiessen, L. D., Byrd, S. A., Goodson, J., Kelly, H., Wheeler, T., & Isakeit, T. (2024, Jan/Spring). Cotton Disease Loss Estimate Committee Report, 2023. The Beltwide Cotton Conference. Fort Worth, TX, USA.
• Hu, J. (2023, August/Summer). A survey of lemon branch canker and wood rot in the deserts of Southern California. The Annual meeting of American Phytopathological Society. Denver, CO.
• Hu, J. (2023, August/Summer). Identification and characterization of fungi associated with lemon woot rot in Arizona. The 12th International Congress of Plant Pathology. Lyon, France.
• Hu, J., Norton, E. R., Hagan, A., Faske, T. R., Hutmacher, R. B., Miller, J., Small, I., Grabau, Z., Kemerait, R. C., Price, P., Allen, T. W., Atwell, S., Idowu, J., Thiessen, L. D., Byrd, S. A., Goodson, J., Kelly, H., Wheeler, T., & Isakeit, T. (2023, Jan/Spring). Cotton Disease Loss Estimate Committee Report, 2022. The Beltwide Cotton Conference. New Orleans, LS USA.
• Zhang, Y., & Hu, J. (2023, December/Winter). Identifying Didymellaceae Associated with Pistachio Plants in Arizona. The Retreat of School of Plant Sciences. Tucson: School of Plant Sciences.
• Hu, J., Norton, E. R., Hagan, A., Faske, T. R., Hutmacher, R. B., Miller, J., Small, I., Grabau, Z., Kemerait, R. C., Price, P., Allen, T. W., Atwell, S., Idowu, J., Thiessen, L. D., Byrd, S. A., Goodson, J., Kelly, H., Wheeler, T., Isakeit, T., & Mehl, H. L. (2022, Jan/Spring). Cotton Disease Loss Estimate Committee Report, 2021. The Beltwide Cotton Conference. San Antonio, TX USA.
• Hu, J., Sanogo, S., & Sherman, J. (2022, September/Fall). Molecular characterization of a chile pepper isolate of Beet curly top virus in Arizona. The 25th International Pepper Conference. Tucson.
• Mehl, H. L., Isakeit, T., Wheeler, T., Kelly, H., Goodson, J., Byrd, S. A., Thiessen, L. D., Idowu, J., Atwell, S., Allen, T. W., Price, P., Kemerait, R. C., Grabau, Z., Small, I., Miller, J., Hutmacher, R. B., Faske, T. R., Hagan, A., Norton, E. R., & Hu, J. (2022, Jan/Spring). Cotton Disease Loss Estimate Committee Report, 2022. The Beltwide Cotton Conference. San Antonio, TX, USA: National Cotton Council.
• Mehl, H. L., Hu, J., Isakeit, T., Norton, E. R., Wheeler, T., Hagan, A., Kelly, H., Faske, T. R., Goodson, J., Hutmacher, R. B., Byrd, S. A., Miller, J., Thiessen, L. D., Small, I., Idowu, J., Grabau, Z., Kemerait, R. C., Atwell, S., Price, P., , Allen, T. W., et al. (2022, Jan/Spring). Cotton Disease Loss Estimate Committee Report, 2021. The Beltwide Cotton Conference. San Antonio, TX, USA: National Cotton Council.
• Hu, J., Norton, E. R., Hagan, A., Faske, T. R., Hutmacher, R. B., Miller, J., Small, I., Grabau, Z., Kemerait, R. C., Price, P., Allen, T. W., Atwell, S., Idowu, J., Thiessen, L. D., Byrd, S. A., Goodson, J., Kelly, H., Wheeler, T., Isakeit, T., & Mehl, H. L. (2020, Jan/Spring). Cotton Disease Loss Estimate Committee Report, 2019. The Beltwide Cotton Conference. Austin, TX, USA: National Cotton Council.
• Hu, J., Norton, E. R., Hagan, A., Faske, T. R., Hutmacher, R. B., Miller, J., Small, I., Grabau, Z., Kemerait, R. C., Price, P., Allen, T. W., Atwell, S., Idowu, J., Thiessen, L. D., Byrd, S. A., Goodson, J., Kelly, H., Wheeler, T., Isakeit, T., & Mehl, H. L. (2021, Jan/Spring). Cotton Disease Loss Estimate Committee Report, 2020. The Beltwide Cotton Conference. Memphis, TN, USA: National Cotton Council.
• Hu, J. (2019, August). In vitro evaluation of fungicides for the management of citrus brown wood rot in Arizona. The Annual Meeting of American Phytopathological Society. Cleveland, OH.
• Hu, J. (2019, January). Fusarium species and Fusarium wilt pathogens associated with roots of cottons in Arizona. The Beltwide Cotton Conference. New Orleans LA: Cotton Incorporated.
• Hu, J., Norton, E. R., Hagan, A., Faske, T. R., Hutmacher, R. B., Miller, J., Small, I., Grabau, Z., Kemerait, R. C., Price, P., Allen, T. W., Atwell, S., Idowu, J., Thiessen, L. D., Byrd, S. A., Goodson, J., Kelly, H., Wheeler, T., Isakeit, T., & Mehl, H. L. (2019, Jan/Spring). Cotton Disease Loss Estimate Committee Report, 2018. The Beltwide Cotton Conference. New Orleans LA USA.
• Hu, J., Jiang, J., & Wang, N. (2018, August). Control of citrus Huanglongbing (HLB) via trunk injection of plant activators and antibiotics. The Annual Meeting of Amercian Phytopathological Scociety. Boston, MA USA.
• Hu, J., Norton, E. R., Hagan, A., Faske, T. R., Hutmacher, R. B., Miller, J., Small, I., Grabau, Z., Kemerait, R. C., Price, P., Allen, T. W., Atwell, S., Idowu, J., Thiessen, L. D., Byrd, S. A., Goodson, J., Kelly, H., Wheeler, T., Isakeit, T., & Mehl, H. L. (2018, Jan/Spring). Cotton Disease Loss Estimate Committee Report, 2017. The Beltwide Cotton Conference. San Antonio, TX.
• Hu, J., Jiang, J., & Wang, N. (2017, June). Integrated control of citrus greening with trunk injection of SAR inducers and antibiotics. The Annual Meeting of Pacific Division Meeting, Amercian Phytopathological Scociety. Riverside, CA, USA.

Reviews

• Hu, J., & Ottman, M. J. (2017. Understanding the Stripe Rust Disease. https://agriculture.az.gov/sites/default/files/documents/2017%20Final%20Newsletter.pdf.

Others

• Wright, G. C., & Hu, J. (2019, July). Coupling Spore Traps and Quantitative PCR Assays for Detection and Quantification of Airborne Spores of Antrodia sinuosa in Lemon Orchards of Yuma - 2018. Arizona Citrus Research Council Website https://agriculture.az.gov/arizona-citrus-research-council-previously-funded-research-projects. https://agriculture.az.gov/sites/default/files/documents/Coupling%20Spore%20Traps%20and%20Quantitative%20PCR%20Assays%20for%20Detection%20and%20Quantification%20of.......%20-%202018.pdf
• Hu, J. (2007, May). Phytophthora nicotianae: Fungicide Sensitivity, Fitness, and Molecular Markers.
  More info

  ii DEDICATION iv ACKNOWLEDGMENTS v ATTRIBUTION vi TABLE OF CONTENTS vii LIST OF TABLES xii LIST OF FIGURES xiv Chapter 1 Background: Fungicide resistance, Phytophthora nicotianae and P. cinnamomi