Progress 07/01/10 to 06/30/15
Outputs
OUTPUTS: Phenotype stability, fitness and competitive ability of pyrimethanil-resistant isolates of Penicillium expansum were determined. Pyrimethanil resistance was retained at the levels similar to that of the initial generation after 20 and 5 transfers on PDA and 4 and 3 cycles on apple fruit at 20 and 0 degrees C, respectively. In general, there were no significant differences in the mean values of fitness parameters among the phenotype groups, though variability in individual fitness parameters was observed among the isolates within the same phenotype groups. After 4 disease cycles on apple fruit inoculated with a pair mixture of a sensitive isolate and one of the two resistant phenotypes at 75:25, 50:50 or 25:75 ratios, the final frequency of resistant individuals was significantly decreased compared to the initial generation except that when the mixture consisted of 75% highly pyrimethanil-resistant individuals, the frequency was increased. The results suggest that pyrimethanil resistance was stable and that pyrimethanil resistance did not significantly impair individual fitness parameters, but resistant phenotypes exhibited some competitive disadvantage when the pyrimethanil-resistant individuals were < 50% in the population. Postharvest fungicides were evaluated for control pyrimethanil-resistant strains of P. expansum on apple fruit. Pyrimethanil applied as Penbotec only partially controlled blue mold incited by a low-resistance strain, and failed to control blue mold caused by strains exhibiting moderate or high resistance to pyrimethanil. Fludioxonil applied as Scholar was effective to control pyrimethanil-resistant strains on apple fruit regardless of pyrimethanil-resistant phenotypes. Speck rot caused by Phacidiopycnis washingtonensis and Sphaeropsis rot caused by Sphaeropsis pyriputrescens are two recently reported postharvest diseases of apple. Fruit infection by the pathogens occurs in the orchard but remains latent before harvest. Symptoms develop after harvest and are similar to that of gray mold caused by Botrytis cinerea. PCR assays were developed for disease diagnosis and early detection of latent infection of apple by Phacidiopycnis washingtonensis and Sphaeropsis pyriputrescens. Species-specific primers based on sequences of the rDNA-internal transcribed spacer region were designed for use in PCR assays. Conventional and real-time PCR assays were developed and validated using fruit artificially inoculated with P. washingtonensis, S. pyriputrescens or B. cinerea in comparison with identifications as determined using traditional isolation-based assays. For wound-inoculated fruit, the PCR assays consistently provided the correct identification of the pathogen used as the inoculant in 6 hours of processing time, compared to 5-6 days using culture-based methods. Real-time PCR assays effectively detected latent infections in symptomless stem and calyx tissues of fruit that were inoculated with the pathogens in the orchard during the growing season. PARTICIPANTS: R. J. Boal TARGET AUDIENCES: Researchers; tree fruit growers and packers PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Understanding biological and ecological characteristics of pyrimethanil resistance in Penicillium expansum will help us develop fungicide resistance management programs for blue mold control. Accurate diagnosis of Sphaeropsis rot caused by S. pyriputrescens and speck rot caused by Phacidiopycnis washingtonensis is important to the fruit inspection process, particularly in the instance of fruit destined for export. The PCR assays developed in this study provide a rapid, accurate method for diagnosis and early detection of these diseases.
Publications
- Yin, Y. N., Kim, Y. K., and Xiao, C. L. 2012. Molecular characterization of pyraclostrobin resistance and structural diversity of the cytochrome b gene in Botrytis cinerea from apple. Phytopathology 102:315-322.
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Progress 01/01/11 to 12/31/11
Outputs
OUTPUTS: Resistance to pyrimethanil (Penbotec) has developed in Penicillium expansum populations in some packinghouses where the fungicide as a postharvest drench has been used annually for 4-5 consecutive years. In one packinghouse, over 90% of the isolates were resistant to pyrimethanil when Penbotec (pyrimethanil) was again used on 2010 crops, while on the fruit drenched with Scholar (fludioxonil) in 2010, resistance frequency was reduced to 4%. In another packinghouse where Penbotec was used during 2005-2009 but only Scholar was used on 2010 crops, and the frequency of pyrimethanil resistant strains was reduced from 7% in 2010 (reported in 2010) to 1% in 2011. The results clearly demonstrated the benefit of rotation of postharvest fungicides for drench. In three other packinghouses, neither Penbotec nor Scholar had been widely used before 2010. No pyrimethanil resistance was detected in these three packinghouses. The findings support our recommendations on rotation of postharvest fungicides as a drench, and fungicide resistance management practices need to be implemented in the industry. The frequency of Pristine-resistant strains in apple orchards where Pristine had been used during 2005-2010 declined from the 2010 to 2011 seasons. Fungicides used in these orchards and perhaps other factors such as competitive disadvantage of Pristine-resistant strains may affect the dynamic of Pristine-resistant populations. The results may suggest that Pristine can still be used and remain effective when the resistant populations decline. Reduced rates of tank-mixture of Pristine and Topsin M significantly reduced incidence of gray mold caused by the Pristine-sensitive strain but not the Pristine-resistant strain. Reduced rates of tank-mixture of BAS 703 and Topsin M significantly reduced incidence of gray mold caused by either Pristine-sensitive or Pristine-resistant strains but was more effective against the Pristine-sensitive strain. In 2011, we repeated the experiment with an emphasis on a tan-mixture of full label rates of Pristine and Topsin for control of Pristine-resistant strains. The results will be forthcoming. Although DPA is not a fungicide, TBZ-resistant isolates became sensitive to DPA and a DPA treatment significantly controlled gray mold caused by TBZ-resistant strains. Resistance to the AP fungicides compromised the efficacy of pyrimethanil as a postharvest treatment for control of gray mold. Fludioxonil was effective against all phenotypes. The results suggest that the use of AP fungicides in the orchards should be limited to minimize the risk of development of resistance to the postharvest fungicide Penbotec (pyrimethanil). Preharvest applications of the biocontrol agents Serenade MAX or Sonata did not significantly reduce postharvest rots in comparison with the nontreated control. PARTICIPANTS: R. J. Boal TARGET AUDIENCES: Researchers; and tree fruit growers and packers PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Establishing a monitoring program for the early detection of resistance to the two new apple-postharvest fungicides, fludioxonil and pyrimethanil, in Penicillium expansum is important to the development and implementation of fungicide-resistance management practices for apple production. Further research is needed to understand the biological and ecological characteristics of pyrimethanil resistance in P. expansum, determine whether the level of pyrimethanil resistance results in the failure of blue mold control with pyrimethanil, and develop relevant measures to manage pyrimethanil resistance. Understanding biological characteristics of boscalid resistance and pyraclostrobin resistance in field isolates of B. cinerea will help us develop fungicide resistance management programs for gray mold control.
Publications
- Xiao, C. 2011. Stability and fitness of pyraclostrobin- and boscalid-resistant phenotypes in field isolates of Botrytis cinerea from apple. Phytopathology. 101:1385-1391.
- Xiao, C. 2011. Molecular characterization of boscalid resistance in field isolates of Botrytis cinerea from apple. Phytopathology. 101:986-995.
- Xiao, C., and R.J.Boal. 2011. Control of Sphaeropsis rot in stored apples caused by Sphaeropsis pyriputrescens with postharvest fungicides. Plant Disease. 95:1075-1079.
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Progress 01/01/10 to 12/31/10
Outputs
OUTPUTS: Pyrimethanil resistance is emerging in Penicillium expansum populations in some packinghouses where the fungicide as a postharvest drench has been used annually for 4-5 consecutive years. In one packinghouse, over 80% of the P. expansum isolates obtained from decayed fruit were resistant to pyrimethanil, resulting in the loss of blue mold control on Penbotec-drenched fruit. The results indicated that fungicide resistance practices need to be implemented in order to manage pyrimethanil resistance. Isolates of P. expansum remained sensitive to fludioxonil. TBZ-resistant strains were still present in sampled packinghouses, indicating that TBZ-resistant strains remained in P. expansum populations even after TBZ was not used. In orchards where Pristine had been used for 4-5 consecutive years, frequency of Pristine resistance in the gray mold fungus Botrytis cinerea ranged from 13 to 54%, whereas it was only approximately 2% in an orchard where Pristine had been used for only one year. The results indicated that repeated annual use of Pristine increased the population of Pristine-resistant B. cinerea in the orchards and that practices for managing Pristine resistance are needed. Boscalid only delayed conidial germination and had no fungicidal activity against Penicillium expansum. Pyraclostrobin and Pristine appeared to only have suppressive activity against P. expansum. Boscalid resistance and pyraclostrobin resistance in B. cinerea were stable. However, boscalid-resistant and pyraclostrobin-resistant strains had disadvantages in competing with fungicide-sensitive strains of B. cinerea, suggesting that if the use of these fungicides is discontinued in the orchard, frequency of resistant populations will likely decline. All Pristine-resistant isolates that were sensitive to TBZ were insensitive to DPA. However, Pristine-resistant isolates that were also resistant to TBZ became sensitive to DPA. The results indicated that Pristine resistance does not alter the sensitivity of the isolates to DPA but there is a negative cross resistance between TBZ and DPA. The lab test results suggest that DPA may be able to control TBZ-resistant strains of B. cinerea, though DPA is not a fungicide. PARTICIPANTS: Chang-Lin Xiao, Robin Boal TARGET AUDIENCES: Apple industry, agricultural chemical industry, researchers PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Establishing a monitoring program for early detection of reduced sensitivity of Penicillium expansum to the two new apple-postharvest fungicides, fludioxonil and pyrimethanil, is important to development and implementation of fungicide-resistance management practices for apple production. Further research is needed to monitor the frequency of pyrimethanil-resistant populations, understand the biological characteristics of pyrimethanil resistance in P. expansum, determine whether the level of pyrimethanil resistance results in the failure of blue mold control with pyrimethanil, and develop relevant measures to manage pyrimethanil resistance. Understanding biological characteristics of boscalid resistance and pyraclostrobin resistance in field isolates of B. cinerea will help us develop fungicide resistance management programs for gray mold control.
Publications
- Kim, J., B.Campbell, N.Mahoney, K.Chan, R.Molyneux, and C.Xiao. 2010. Use of chemosensitization to overcome fludioxonil-resistance in Penicillium expansum. Letters in Applied Microbiology. 51:177-183.
- Kim, Y., and C.Xiao. 2010. Influence of environmental factors on conidial germination and survival of Sphaeropsis pyriputrescens. European Journal of Plant Pathology / European Foundation for Plant Pathology. 126:153-163.
- Zhao, H., L.Huang, C.Xiao, J.Liu, J.Wei, and X.Gao. 2010. Influence of culture media and environmental factors on mycelial growth and conidial production of Diplocarpon mali. Letters in Applied Microbiology. 50:639-644.
- Xiao, C. 2010. Control of postharvest diseases in apples with reduced-risk fungicides. Stewart Postharvest Review.
- Xiao, C., Y.Kim, and R.J.Boal. 2010. First report of occurrence of pyrimethanil resistance in Penicillium expansum from stored apples in Washington State. Plant Disease. 95:72.
- Kim, Y., and C.Xiao. 2010. Resistance to pyraclostrobin and boscalid in populations of Botrytis cinerea from stored apples in Washington State. Plant Disease. 94:604-612.
- Zhao, H., Y.Kim, L.Huang, and C.Xiao. 2010. Resistance to thiabendazole and baseline sensitivity to fludioxonil and pyrimethanil in Botrytis cinerea populations from apple and pear in Washington State. Postharvest Biology and Technology. 56:12-18.
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Progress 01/01/09 to 12/31/09
Outputs
OUTPUTS: In 2009, 186 and 16 isolates of Penicillium expansum were collected from pyrimethanil-drenched and fludioxonil-drenched apple fruit, respectively. All isolates were screened for resistance to pyrimethanil based on a conidial germination assay and resistance to fludioxonil based on a mycelial growth assay. One isolate from pyrimethanil-drenched fruit showed significant resistance to pyrimethanil. EC50 values of pyrimethanil based on a mycelial growth assay for a subset of 37 pyrimethanil-sensitive isolates ranged from 0.632 to 1.518 mg/L, with a mean of 1.07 mg/L, which is within the baseline sensitivity. All isolates were sensitive to fludioxonil. This was the first time we observed the occurrence of pyrimethanil resistance among the isolates of P. expansum from pyrimethanil-drenched fruit, but the frequency was low. Pristine was applied to Fuji apples 7 days before harvest. Fruit were removed from storage 5 months after harvest, washed and brushed through a research packing line, wounded and inoculated with P. expansum and treated with either BioSave or a fungicide. Inoculated fruit were stored at 0 degrees C in air for 8 weeks and one additional week at room temperature. Residual protection of apple fruit by Pristine was still evident 5 months after harvest but declined significantly after the fruit was stored at room temperature for one week after CA storage. BioSave alone reduced blue mold incidence to 30% during the 8-week cold storage. Preharvest Pristine plus postharvest BioSave further reduced blue mold incidence to 2.5% during cold storage. However, the effectiveness of these treatments declined after the fruit was stored at room temperature for one week after cold storage. Two experiments (one on Fuji and one on Red Delicious) were conducted on the 2008 crops and completed in late spring 2009. On Fuji, both fludioxonil and pyrimethanil on drenched fruit exhibited very good residual protection of fruit from infection by P. expansum. BioSave alone applied at packing reduced blue mold incidence to 33-43%, but the effectiveness was lost when the fruit was stored for one additional week at room temperature after cold storage. Bio-Save did not provide additional protection for fludioxonil-drenched or pyrimethanil-drenched fruit. PARTICIPANTS: Chang-Lin Xiao, Yong-Ki Kim, Robin Boal TARGET AUDIENCES: Scientific community and apple industry PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Establishing a monitoring program for early detection of reduced sensitivity of Penicillium expansum to the two new apple-postharvest fungicides, fludioxonil and pyrimethanil, is important to the development and implementation of fungicide-resistance management practices for apple production. Further research is needed to monitor the frequency of pyrimethanil-resistant populations, understand the biological characteristics of pyrimethanil resistance in P. expansum, determine whether the level of pyrimethanil resistance results in the failure of blue mold control with pyrimethanil, and develop relevant measures to manage pyrimethanil resistance. Pre- and postharvest integrated programs using reduced-risk fungicides and a biocontrol agent will provide important tools to the apple industry in Washington State for control of major postharvest diseases of apple. These disease-control programs not only reduce economic losses resulting from postharvest diseases affecting apples but also provide sound strategies and tactics for management of fungicide resistance in postharvest pathogens in the orchard/storage system for apple production.
Publications
- Liu, Q., T. Peever, and C. Xiao. 2009. Population structure of Potebniamyces pyri in the U.S. Pacific Northwest and evidence of outcrossing inferred with sequence-characterized amplified region markers. Phytopathology. 99:532-539.
- Xiao, C., and R.J. Boal. 2009. Preharvest application of a boscalid and pyraclostrobin mixture to control postharvest gray mold and blue mold in apples. Plant Disease. 93:185-189.
- Spotts, R.A., M. Serdani, K.M. Wallis, M. Walter, T. Harris-Virgin, K. Spotts, D. Sugar, C. Xiao, and A.P. Qu. 2009. At-harvest prediction of gray mold risk in pear fruit in long-term cold storage. Crop Protection. 28:414-420.
- Liu, Q., and C. Xiao. 2009. Infection of dAnjou pear fruit by Potebniamyces pyri in the orchard in relation to Phacidiopycnis rot during storage. Plant Disease. 93:1059-1064.
- Spotts, R.A., K. Seifert, K.M. Wallis, D. Sugar, C. Xiao, M. Serdani, and J.L. Henriquez. 2009. Description of Cryptosporiopsis kienholzii and species profiles of Neofabraea in major pome fruit growing districts in the Pacific Northwest USA.. Mycological Research. 113:1301-1311.
- Xiao, C., and R.J. Boal. 2009. Residual activity of fludioxonil and pyrimethanil against Penicillium expansum on apple fruit. Plant Disease. 93:1003-1008.
- Xiao, C., Y. Kim, and R.J. Boal. 2009. A new canker disease of crabapple trees caused by Phacidiopycnis washingtonensis in Washington State. Plant Health Progress. :doi:10.1094/PHP-2009-0612-01-BR.
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Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: Residual activity of fludioxonil and pyrimethanil in apple fruit against P. expansum, the cause of blue mold, was investigated. Organic Red Delicious fruit harvested from a commercial orchard was either not treated or drenched with fludioxonil, pyrimethanil, or thiabendazole at the label rates prior to storage and then stored in controlled atmosphere (CA) at 0C for 5 and 7 months, after which time the fruit was removed from storage and subjected to washing and brushing during packing. Fruit was then wounded and inoculated with conidial suspensions of P. expansum. Inoculated fruit was treated either with sterile water or fungicides. Fruit was stored at 0C for 8 weeks and at room temperature for one additional week after cold storage. No decay or up to 26% blue mold incidence was observed on fludioxonil-drenched fruit that was not treated with fungicides at packing. No decay or less than 4% blue mold incidence was observed on pyrimethanil-drenched fruit that was not treated with fungicides at packing, whereas 65-99% blue mold incidence was observed on thiabendazole-drenched fruit that was not treated with fungicides at packing. The results indicate that residual effects of fludioxonil and pyrimethanil applied prior to storage on blue mold in Red Delicious fruit can last for at least 7 months under apple-storage conditions. Preharvest application of Pristine (a premixed formulation of pyraclostrobin and boscalid) in combination with postharvest BioSave (a biocontrol strain of Pseudomonas syringae) for blue mold control was investigated. Pristine was applied to Fuji apples 7 days before harvest. Fruit was stored in CA for 5 months, washed and brushed through a research packing line, wounded and inoculated with P. expansum. Inoculated fruit was stored at 0C in air for 8 weeks and one additional week at room temperature. Preharvest Pristine without any postharvest biocontrol or fungicide reduced blue mold incidence to 20% after 8 weeks at 0C. Pristine in combination with postharvest BioSave further reduced blue mold to 2.5%. The effectiveness of Pristine plus postharvest BioSave was reduced after the fruit was stored at room temperature for one additional week after cold storage. However, the size of decay on the fruit treated with preharvest Pristine and postharvest BioSave was significantly smaller than that on the fruit treated with preharvest Pristine without postharvest BioSave. Pre- and postharvest fungicides were evaluated for control of Sphaeropsis rot caused by S. pyriputrescens in apples. Two different timings of infection (2 and 5 weeks before harvest) were included in the test to evaluate whether timing of infection affects the effectiveness of fungicide treatments. Pristine, thiophanate-methyl, and ziram significantly reduced Sphaeropsis rot compared to the nontreated control. The three apple-postharvest fungicides (thiabendazole, fludioxonil, and pyrimethanil) statistically were equally effective for control, but a pyrimethanil-drench treatment completely eradicated infections regardless of timing of infection before harvest. PARTICIPANTS: Chang Lin Xiao, Yong Ki Kim, Robin J. Boal TARGET AUDIENCES: Researchers, agrichemical industry, apple growers and packers. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Pre- and postharvest integrated programs using reduced-risk fungicides and a biocontrol agent will provide important tools to the apple industry in Washington State for control of major postharvest diseases of apple. These disease-control programs not only reduce economic losses resulting from postharvest diseases affecting apples but also provide sound strategies and tactics for management of fungicide resistance in postharvest pathogens in the orchard/storage system for apple production.
Publications
- Xiao, C., and R.J. Boal. 2008. Control of Phacidiopycnis rot in d'Anjou pears. Acta Horticulturae 800:935-939.
- Li, H., and C. Xiao. 2008. Characterization of fludioxonil-resistant and pyrimethanil-resistant phenotypes of Penicillium expansum from apple. Phytopathology. 98:427-435.
- Kim, Y., and C. Xiao. 2008. Distribution and incidence of Sphaeropsis rot in apple in Washington State. Plant Disease. 92:940-946.
- Xiao, C., and Y. Kim. 2008. Postharvest fruit rots in apples caused by Botrytis cinerea, Phacidiopycnis washingtonensis, and Sphaeropsis pyriputrescens. Plant Health Progress. (doi:10.1094/PHP-2008-0919-01-DG).
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Progress 01/01/07 to 12/31/07
Outputs
OUTPUTS: Baseline sensitivity to fludioxonil and pyrimethanil in Penicillium expansum populations from Washington State was established. Based on mycelial growth assays, baseline EC50 values ranged from 0.011 to 0.068 (avg. = 0.020) mg/L for fludioxonil and from 0.519 to 2.054 (avg. = 1.340) mg/L for pyrimethanil. One isolate showed reduced sensitivity to fludioxonil with an EC50 of 0.068 mg/L, which was significantly higher than those of remaining isolates tested. Fludioxonil at 0.5 mg/L completely inhibited mycelial growth of all isolates tested except for the isolate with reduced sensitivity. Conidial germination and germ-tube elongation were completely inhibited by pyrimethanil at 0.5 mg/L and by fludioxonil at 0.1 mg/L except for the isolate with reduced sensitivity based on the mycelial growth assay. Discriminatory concentrations of 0.5 mg/L fludioxonil for mycelial growth and 0.5 mg/L pyrimethanil for germ-tube elongation were recommended for phenotyping isolates of P.
expansum for resistance to these two fungicides. The potential risk of resistance development in P. expansum to the new postharvest fungicides was assessed. Six fungicide-resistant phenotypes were identified among the parental wild-type isolates and their mutants based upon their resistance levels. All four fludioxonil highly-resistant mutants were sensitive to pyrimethanil and retained the same phenotypes of resistance to TBZ as the parental isolates. All four pyrimethanil-resistant mutants had a low level of resistance to fludioxonil. The two pyrimethanil-resistant mutants derived from a TBZ-S isolate became resistant to TBZ at 5 ug/ml and retained the same phenotypes as the original generations, after 20 successive generations on PDA and four generations on apple fruit. All mutants were pathogenic on apple fruit at both 0 and 20 degrees C, but fludioxonil highly-resistant mutants were less virulent and produced fewer conidia on apple fruit than pyrimethanil-resistant mutants and
their parental wild-type isolates. Compared to the parental isolates, all four fludioxonil highly-resistant mutants had an increased sensitivity to osmotic stress on PDA amended with NaCl, while the pyrimethanil-resistant mutants did not. Pyrimethanil was effective against blue mold caused by fludioxonil-resistant mutants at both 0 and 20 degrees C. Pyrimethanil and fludioxonil reduced blue mold incited by pyrimethanil-resistant mutants during 12-week storage at 0 degrees C but were not effective at 20 degrees C. TBZ was not effective against pyrimethanil-resistant mutants derived from TBZ-S wild-type isolates at room temperature but provided some control at 0 degrees C. The results indicate that: i) a fitness cost was associated with fludioxonil highly-resistant mutants of P. expansum in both saprophytic and pathogenic phases of the pathogen but not pyrimethanil-resistant mutants; ii) pyrimethanil possessed a higher risk than fludioxonil in the development of resistance in P.
expansum; and iii) triple resistance to the three apple-postharvest fungicides could emerge and become a practical problem if resistance to pyrimethanil develops in P. expansum populations.
PARTICIPANTS: Hongxia Li; Robin Boal; Yong-Ki Kim
TARGET AUDIENCES: Researchers; agrichemical industry; apple growers and packers
PROJECT MODIFICATIONS: None
Impacts
The information generated in this study on the baseline sensitivity to new postharvest fungicides and on the risk assessment of fungicide resistance in P.expansum populations is useful in monitoring future shifts in sensitivities to these two new fungicides in P. expansum populations from apple in the region. Pre- and postharvest integrated programs to be developed in this study will provide important tools to the apple industry in Washington State for control of major postharvest diseases of apple. These disease-control programs not only reduce economic losses resulting from postharvest diseases affecting apples but also provide sound strategies and tactics for management of fungicide resistance in postharvest pathogens in the orchard/storage system for apple production.
Publications
- Li, H., and C.Xiao. 2008. Baseline sensitivities to fludioxonil and pyrimethanil in Penicillium expansum populations from apple in Washington State. Postharvest Biology and Technology. 47(2):239-245.
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Progress 01/01/06 to 12/31/06
Outputs
Over the 3-year statewide survey of postharvest diseases on Red Delicious, Fuji and Golden Delicious, Sphaeropsis rot caused by Sphaeropsis pyriputrescens accounted for 18.4% of the total decay. Instances of severe losses of fruit due to Sphaeropsis rot in storage have been observed in both Red Delicious and Fuji apples. The survey results indicate that Sphaeropsis rot should be considered one of the major targets for decay control in the region. Sources and availability of S. pyriputrescens inoculum were monitored in two apple orchards. Dead tissues on fruit spurs, dieback twigs or cankers, and crabapple trees were important sources of inoculum responsible for infection of apple fruit in the orchard leading to Sphaeropsis rot during storage. Viable inoculum of the fungus was available throughout the fruit-growing season. Significant cankers developed on twigs inoculated in November and early spring. No significant cankers developed on twigs inoculated in June. It
appeared that trees were more susceptible to infection during the dormant period. Sphaeropsis rot developed on early-inoculated fruit as well as late-inoculated fruit during the fruit-growing season, indicating that when conditions were met the fungus was able to colonize the fruit even in the early season and to remain latent throughout the fruit-growing season. Overall, incidence of Sphaeropsis rot on inoculated fruit increased as the inoculation date approached harvest. In 2006 experiments, Pristine and Topsin applied at 7 days before harvest significantly reduced Sphaeropsis rot on apple fruit that were inoculated with the Sphaeropsis fungus at either 5 or 2 weeks before harvest, respectively. Timing of infection of fruit by the Sphaeropsis fungus may affect the effectiveness of preharvest fungicides for control of Sphaeropsis rot. Mertect applied as a pre-storage drench treatment was consistently effective to control Sphaeropsis rot. Sequence characterized amplified region (SCAR)
markers were developed and used to determine the population structure of Potebniamyces pyri in five major d'Anjou pear-production areas in the Pacific Northwest. Segregation of alleles at five SCAR loci among ascospore progeny sets revealed that 17 of 20 apothecia had at least one marker segregating, indicating that the apothecium was outcrossed. These data suggest that P. pyri is likely a heterothallic fungus but has a mixed mating system in nature with approximately 85% of apothecia outcrossed and 15% selfed in the same fungal population. In 2006 experiments, Topsin and Pristine reduced stem-end and calyx-end Phacidiopycnis rot by 86% and 41%, respectively, in comparison with the nontreated control. When applied as a pre-storage drench treatment, all three postharvest fungicides were effective to control stem-end and calyx-end Phacidiopycnis rot. Mertect and Scholar reduced stem- and calyx-end Phacidiopycnis rot by 95% and 88%, respectively, in comparison with the nontreated
control. Penbotec was highly effective and no stem- and calyx-end Phacidiopycnis rot developed in the fruit treated with Penbotec.
Impacts
Sphaeropsis rot and Phacidiopycnis rot are two recently reported postharvest diseases of pome fruits in the United States. Information on the occurrence of Sphaeropsis rot and fruit rots caused by other pathogens would help develop relevant control measures to target major postharvest diseases in order to reduce overall losses. Information generated from the study on the epidemiology of Sphaeropsis rot would contribute to our understanding of sources and availability of inoculum for infection of fruit in the orchard and timing of fruit infection. Development of pre- and postharvest fungicide programs for control of Sphaeropsis rot in apples and Phacidiopycnis rot in pears would help the tree fruit industry implement relevant effective measures to reduce losses resulting from postharvest diseases. Information generated from studies on the biology of Sphaeropsis pyriputrescens and Potebniamyces pyri would facilitate mycological and pathological research on these two
fungi and diseases they cause.
Publications
- Xiao, C . 2006. Postharvest fruit rots in d'Anjou pears caused by Botrytis cinerea, Potebniamyces pyri, and Sphaeropsis pyriputrescens. Plant Health Progress:Plant Health Progress doi:10.1094/PHP-2006-0905-01.
- Kim, Y., and C. Xiao. 2006. A postharvest fruit rot in apple caused by Phacidiopycnis washingtonensis. Plant Disease 90(11):1376-1381.
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Progress 01/01/05 to 12/31/05
Outputs
In a Fuji orchard infected by Sphaeropsis pyriputrescens, 60-90% of the sampled apple trees infected by the fungus and 27-53% of the sampled dead fruit spurs or twigs were infected. Sources of inoculum of the fungus responsible for fruit infection included dead fruit spurs, dead pedicle of flowers or fruit, and twigs with dieback symptoms or cankers. In a Red Delicious orchard, 20-40% of the sampled trees were infected by the fungus. Dead tissues on fruit spurs appeared to be a common source of inoculum for fruit infection. Viable fruiting bodies of S. pyriputrescens were available throughout the fruit-growing season in the orchard. Cankers and dieback twigs of crabapple trees were not the only sources of inoculum. Crabapple trees, if present, likely facilitated spread of the fungus from crabapple trees to apple trees in the orchard. Fruiting bodies of the fungus on apple trees were the immediate inoculum responsible for infection of fruit in the orchard leading to
Sphaeropsis rot during storage. Significant cankers developed on twigs inoculated in November and early spring. No significant cankers developed on twigs inoculated in June. Fruit of Fuji, Red Delicious and Golden Delicious were susceptible to infection from May to harvest (September or October), but disease symptoms developed only during storage. On Red Delicious, stem and calyx infections both were common; on Golden Delicious, stem infection was more common than calyx infection; on Fuji, calyx infection was more common than stem infection. These observations need to be confirmed in the ongoing study. Fungicides Scholar, Mertect and Pristine were highly effective in inhibiting mycelial growth of the Sphaeropsis fungus, and Penbotec was effective only at higher rates. The information has been used for developing pre- and postharvest fungicide programs for control of Sphaeropsis rot. Ziram applied at two weeks before harvest was effective in reducing losses by Sphaeropsis rot in one
year but not the following year. A postharvest drench with thiabendazole reduced losses by Sphaeropsis rot. When applied at 7 and 14 days before harvest, Pristine was effective against Phacidiopycnis rot and reduced Phacidiopycnis rot by 54-64% in comparison with the nontreated control. Both Scholar and Penbotec at label rates were very effective to control Phacidiopycnis rot originating from infections of skin wounds. After the fruit were inoculated with Potebniamyces pyri, a 24-hour delay of a treatment with either Scholar or Penbotec did not compromise the efficacy. Research is being conducted to determine genetic diversity of Potebniamyces pyri in the Pacific Northwest. Research is also being conducted to determine infection of pear stems by P. pyri in relation to temperature and wetness duration. We described a new fungal species, Phacidiopycnis washingtonensis, which is the cause of a new postharvest fruit rot disease on apple. We determined that P. washingtonensis has the
potential to cause significant fruit losses during storage.
Impacts
Sphaeropsis rot and Phacidiopycnis rot are two recently reported postharvest diseases on pome fruits in the United States. Information on the occurrence of Sphaeropsis rot and fruit rots caused by other pathogens would help develop relevant control measures to target major postharvest diseases in order to reduce overall losses. Information generated from the study on epidemiology of Sphaeropsis rot would contribute to our understanding of sources and availability of inoculum for infection of fruit in the orchard and timing of fruit infection. In vitro sensitivity tests of Sphaeropsis pyriputrescens to common pre- and postharvest fungicides is the first step to develop fungicide programs for disease control and provide basis for strategies of using different classes of fungicides in the orchard or as postharvest treatments for control of Sphaeropsis rot. Information generated from studies on the biology of S. pyriputrescens and Potebniamyces pyri would facilitate
mycological and pathological research on these two fungi and diseases they cause.
Publications
- Kim, Y. K., Xiao, C. L., and Rogers, J. D. 2005. Influence of culture media and environmental factors on mycelial growth and pycnidial production of Sphaeropsis pyriputrescens. Mycologia 97:25-32.
- Liu, Q., and Xiao, C. L. 2005. Influence of nutrient and environmental factors on conidial germination of Potebniamyces pyri. Phytopathology 95:572-580.
- Xiao, C. L., and Boal, R. J. 2005. Distribution of Potebniamyces pyri in the U.S. Pacific Northwest and its association with a canker and twig dieback disease of pear trees. Plant Disease 89:920-925.
- Xiao, C. L., Boal, R. J. 2005. A new canker and twig dieback disease of apple and crabapple trees caused by Sphaeropsis pyriputrescens in Washington State. Plant Disease 89:1130.
- Xiao, C. L., Rogers, J. D., Kim, Y. K., and Liu, Q. 2005. Phacidiopycnis washingtonensis - a new species associated with pome fruits from Washington State. Mycologia 97:464-473.
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Progress 01/01/04 to 12/31/04
Outputs
Sphaeropsis rot is an orchard-related postharvest disease on apples. Of the 78 grower lots sampled in a large-scale survey in 2004, 60 had Sphaeropsis rot. Sphaeropsis rot is an important component of storage decay and could cause significant losses during storage. Overall, Sphaeropsis rot accounted for an average of 18 to19% of the decay on Fuji and Golden Delicious and 22% of the decay on Red Delicious. Severe losses caused by Sphaeropsis rot have been observed on Red Delicious and Fuji. Infection of fruit by S. pyriputrescens occurred in the orchard and symptoms developed during storage. S. pyriputrescens was associated with a twig dieback and canker disease of apple and crabapple trees in apple orchards. In a Fuji orchard with a history of severe Sphaeropsis rot during storage, 100% of the crabapple trees and 43% of the apple trees were infected by S. pyriputrescens. It appeared that pycnidia formed on cankers and dead twigs, and fruit spurs of trees were the
major type of inoculum for infection of fruit in the orchard. The fungus Sphaeropsis pyriputrescens exhibited varying degrees of sensitivity to various fungicides. Broad-spectrum fungicides Captan, Dithane and Ziram were effective in inhibiting both mycelial growth and conidial germination but only at high rates. S. pyriputrescens exhibited different patterns of sensitivity to Procure (a DMI fungicide) and Flint (a strobilurin). S. pyriputrescens is a low-temperature species. Influence of substrate and environmental factors on mycelial growth and pycnidial production of S. pyriputrescens has been determined. Effects of environmental factors on conidial germination have also been determined. Conidia of Potebniamyces pyri germinate in two different manners: budding and developing germ tubes. The mode of conidial germination was nutrient-dependent. Low nutrient levels favored budding, whereas high nutrient levels favored germ tube development. Conidia germinated at 0 to 30 degrees C but
not at 35 degrees C, with optimum temperature between 20 and 25 degrees C. Four to 5 and 6 to 8 h of wetness durations at optimum temperature were required for budding and developing germ tubes, respectively, and 20 to 24 h of wetness was required to reach germination peaks. Secondary conidia, produced by budding of conidia, initially increased their dimensions and later germinated at 0 to 25 degrees C in the same manner as mother conidia. No germination of secondary conidia occurred at 30 degrees C. d'Anjou pear fruit near harvest were more susceptible to infection by Potebniamyces pyri, but infection could also occur during early growing season when environmental conditions were met. None of the six fungicides (Flint, Ziram, Vangard, Procure and Dithane) was able to eliminate P. pyri in twigs that were inoculated with the fungus two weeks before applications of fungicides, and pycnidia containing viable conidia were produced on majority of fungicide-treated twigs.
Impacts
Sphaeropsis rot and Phacidiopycnis rot are two newly reported postharvest diseases of pome fruits in the United States. Information on the occurrence of Sphaeropsis rot and fruit rots caused by other pathogens would help develop relevant control measures to target major postharvest diseases in order to reduce overall losses. Information generated from the study on epidemiology of Sphaeropsis rot would contribute to our understanding of sources and availability of inoculum for infection of fruit in the orchard and timing of fruit infection. In vitro sensitivity tests of Sphaeropsis pyriputrescens to common pre- and postharvest fungicides is the first step to develop fungicide programs for disease control and provide basis for strategies of using different classes of fungicides in the orchard or as postharvest treatments for control of Sphaeropsis rot. Information generated from studies on the biology of S. pyriputrescens and Potebniamyces pyri would facilitate
mycological and pathological research on these two fungi and diseases they cause.
Publications
- Xiao, C. L., and Boal, R. J. 2004. Prevalence and incidence of Phacidiopycnis rot in d'Anjou pears in Washington State. Plant Dis. 88:413-418.
- Xiao, C. L., and Rogers, J. D. 2004. A postharvest fruit rot in d'Anjou pears caused by Sphaeropsis pyriputrescens sp. nov. Plant Dis. 88: 114-118.
- Xiao, C. L., and Sitton, J. W. 2004. Effects of culture media and environmental factors on mycelial growth and pycnidial production of Potebniamyces pyri. Mycological Research 108:926-932.
- Xiao, C. L., Rogers, J. D., and Boal, R. J. 2004. First report of a new postharvest fruit rot on apple caused by Sphaeropsis pyriputrescens. Plant Dis. 88: 233.
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Progress 01/01/03 to 12/31/03
Outputs
Most of Botrytis cinerea isolates tested were sensitive to thiabendazole (TBZ). Approximately 70% of the isolates had EC50 values between 0.41 and 0.60 ppm. Only 1.5% of the isolates tested were highly resistant to TBZ. No TBZ-resistant isolates of B. cinerea were observed among 70 isolates recovered from TBZ-drenched apple fruit. EC50 values of TBZ-sensitive isolates were similar between isolates from non-drenched sources and from TBZ-drenched fruit, indicating that current postharvest decay control recommendations, including avoiding benzimidazole fungicides in orchard and using thiabendazole only after harvest in the packing facility, are an effective measure for fungicide resistance management. The baseline sensitivity of B. cinerea from apple to the fungicide fludioxonil was established. The B. cinerea population from apple in Washington State was sensitive to fludioxonil. All isolates tested have not been exposed to this fungicide. Apparently no cross-resistance
exists in B. cinerea isolates to the two fungicides, thiabendazole and fludioxonil. Fungicide fenhexamid (Elevate) was consistently effective in controlling gray mold originating from wound infection by B. cinerea. Fenhexamid applied one day prior to harvest reduced incidence and severity of postharvest gray mold originating from wound infections by 75-86% and 88-92%, respectively, in comparison with the non-fungicide treated control. Effectiveness of preharvest applications of biocontrol agents in controlling postharvest gray mold and blue mold varied in two-year trials. Overall, they were not effective in reducing incidence of decay originating from wound infections by B. cinerea and Penicillium expansum, though they might reduce severity of decay. The relatively low level of biocontrol yeast or bacteria cells introduced at wounds might be responsible for unsatisfactory control. A new postharvest fruit rot disease on apple and pear was discovered, caused by a newly described fungal
species, Sphaeropsis pyriputrescens Xiao & J.D. Rogers. This disease was first discovered on Anjou pears and later was determined to cause more serious problems on apples. Losses as high as 24% were observed on apples during storage. The disease has been officially named 'Sphaeropsis rot.' Phacidiopycnis rot, caused by Potebniamyces pyri (anamorph Phacidiopycnis piri), is an important component of storage rots in Anjou pears in Washington State. Phacidiopycnis rot causes symptoms of stem-end rot, calyx-end rot, and skin wound-associated rot. P. pyri appears to be widespread in the pear production region in the U.S. Pacific Northwest and is associated with bark necrosis and canker of pear trees.
Impacts
With the increasing commercial use of 1-MCP on fresh apples, fewer apples will be drenched with DPA and TBZ. Alternatives are needed to TBZ drench for decay control. Preharvest use of effective fungicides such as fenhexamid would meet this need for decay control under the new MCP-based fruit handling system for apples. Fenhexamid is considered a low-risk fungicide. Based on the data generated in this research project, an IR-4 request has been submitted for use of fenhexamid as preharvest treatments for control of postharvest gray mold on apples and pears in Washington State. Fungicide resistance management is an important component in postharvest decay control of pome fruits. The baseline sensitivity of B. cinerea to fludioxonil will be useful in monitoring the development of resistance in the B. cinerea populations to this fungicide. The discovery of Sphaeropsis rot and the presence of Phacidiopycnis rot in the U.S. is the first essential step to developing and
implementing relevant measures for disease control.
Publications
- Brunner, J.F., J. Dunley, W. Jones, E.H. Beers, J.V. Tangren, C. Xiao, and G.G. Grove. 2003. Pesticide use and IPM practices in Washington's pear and cherry orchards. Agriculture and Environmental News. No 208, August 2003. (http://aenews.wsu.edu/Aug03AENews/Aug03AENews.htm#PearCherry).
- Brunner, J.F., W. Jones, E.H. Beers, J.V. Tangren, J. Dunley, C. Xiao, and G.G. Grove. 2003. A decade of pesticide use in Washington apple orchards. 2003. Ag. Environ. News. No 205, May 2003, 16 pp.
- Xiao, C.L. 2003. Management of postharvest fruit rot: from orchard to storage. Proc. Wash. State Hort. Assoc. 98th annual meeting, pp. 155-160.
- Xiao, C.L., and R.J. Boal. 2003. Effects of pre-harvest fungicides on postharvest gray mold rot of Fuji apples, 2001-02. Fungicide and Nematicide Tests 58:PF015.
- Xiao, C.L., and R.J. Boal. 2003. Evaluation of fungicide programs for control of apple powdery mildew, 2002. Fungicide and Nematicide Tests 58:PF014.
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Progress 01/01/02 to 12/31/02
Outputs
Botrytis spp. were isolated from floral parts of fruit during bloom in all five commercial orchards sampled in 2002, with isolation frequency ranging from 5 to 50%. Penicillium spp. also were recovered from the calyx tissues of fruit. Inoculation experiments indicated that Botrytis cinerea colonized floral parts of fruit during bloom and survived in these tissues throughout the growing season. Fruits developed from flowers inoculated with the pathogen in 2001 were harvested and stored in air at 0.5 degrees C for decay evaluation in early 2002. Fruits harvested from four commercial orchards were also stored for decay evaluation. No correlation was observed between colonization of floral parts and calyx-end decay in storage. Colonization of floral parts by Botrytis can be used as an indicator of inoculum potential of the pathogen in the orchard. To determine formation of B. cinerea sclerotia on decayed fruits on the orchard floor, in the fall Fuji apples were inoculated
with B. cinerea isolates in the lab. Botrytis-decayed fruits were then placed in mesh bags and laid on the orchard floor. Botrytis-infected fruits were examined for formation of sclerotia in spring. B. cinerea formed sclerotia on decayed fruit in the spring. This indicated that removal of decayed fruit from the orchard floor would be beneficial in reducing inoculum level in the orchard. Thiabendazole (TBZ)-resistant isolates of B. cinerea were recovered from decayed fruits sampled from packinghouses. Reduced sensitivity to TBZ among the isolates also was observed, but most of Botrytis isolates were sensitive to TBZ at 10 ppm. The fungicide fenhexamid (Elevate) was very effective in controlling B. cinerea. Fenhexamid applied one day prior to harvest reduced the incidence and severity of postharvest gray mold on Fuji by 86 and 90%, respectively, in comparison with the non-fungicide treated control (2001-02 experiment). Captan significantly reduced postharvest gray mold compared with the
non-fungicide treated control, but it did not provide satisfactory control. Preharvest applications of fenhexamid and captan were not effective for control of postharvest blue mold rot originating from wound infections by Penicillium expansum. The yeast Cryptococcus laurentii 87-108, applied one day before harvest, significantly reduced gray mold incidence originating from wound infections by B. cinerea on Fuji (harvested in late October) but not Gala (harvested in late August) compared with the non-treated control. It had no effect on blue mold rot originating from wound infections by P. expansum. Two commercialized biocontrol agents, Bio-Save and Aspire, applied one day before harvest did not provide good control of gray mold on Fuji. The relatively low level of the yeast cells introduced at the wound might be responsible for the unsatisfactory control. This also indicated that increasing the concentration of yeast cells at spray and maintaining a high population level of the
biocontrol yeast on fruit surfaces before harvest are important in order to improve control efficacy.
Impacts
With the increasing commercial use of SmartFresh (1-MCP) on fresh apples, fewer apples will be drenched with TBZ. Gray mold rot will likely cause more losses on non-drenched apples if fruit is not treated with fungicides before storage. Alternatives to TBZ drench for decay control are needed. Preharvest strategy of using effective fungicides such as fenhexamid and biocontrol agents would meet this need for decay control under the new postharvest fruit handling system. Information generated from this study will advance our understanding of Botrytis populations associated with apples.
Publications
- No publications reported this period
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Progress 01/01/01 to 12/31/01
Outputs
Botrytis cinerea, the causal agent of gray mold of stored apples, was recovered from previous season's thinned fruits on the orchard floor with isolation frequency ranging from 2-10%, indicating that orchard floor sanitation to remove thinned fruits would presumably reduce the inoculum level of the pathogen in the orchard. However, no B. cinerea was recovered from the current year's thinned fruit on the orchard floor. B. cinerea was isolated from floral parts of fruit during bloom in all 10 commercial orchards in different areas in Washington State, with isolation frequency ranging from 3-80%. B. cinerea and Penicillium spp. were also recovered from the calyx tissues of fruit during summer and at harvest. Results from the inoculation experiment indicated that B. cinerea colonized floral parts of fruit during bloom and survived in these tissues throughout the growing season. Isolates of Botrytis from apples had remarkable variation in sporulation, sclerotia formation
and pathogenicity. Characterization of Botrytis populations associated with tree fruits in Washington State is being conducted. Orchard surveys indicated that bacterial canker of sweet cherry, caused by Pseudomonas syringae pv. syringae, occurred at low incidence in the Yakima and Wenatchee areas in WA, but severe epidemics have been observed at some specific sites. The disease was more prevalent in the northern fruit production areas from Pateros to Oroville in WA. The strains of Pseudomonas syringae isolated from cherry orchards exhibited varying levels of tolerance to copper, with 82% of strains having tolerance to copper at 0.25 mM CuSO4 in vitro tests.
Impacts
The information generated from this project will advance the understanding of Botrytis populations associated with stored apples and other tree fruits commercially grown in WA and helps the tree fruit industry improve the control of postharvest diseases.
Publications
- No publications reported this period
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