Progress 07/15/08 to 07/14/10
Outputs
OUTPUTS: The field studies proved our hypothesis that altering the application time of this biocontrol treatment would enhance its efficacy and the level of control achieved was equivalent to the registered fungicide treatments. All objectives outlined in the proposal were successfully completed. The results obtained in the project were disseminated by three different avenues to the stakeholders. First, the California Leafy Greens Board conducts two meetings per year to learn of new research developments that would impact the industry. The meetings are held in the central coastal California in March and October each year and are attended by conventional and organic leafy greens growers from throughout California, seed industry representatives, pest control advisors, chemical and biocontrol product industry representatives. The results from the project were presented at these meetings over the past year. Second, the progress in the project over the past year was also summarized in a report to the Leafy Greens Board annual report. Third, a full length final report was also submitted to the biocontrol company representatives. I have also fielded calls from other institutions regarding the performance of this biocontrol product on diseases caused by Sclerotinia species. <p> This project provides immediate benefit to the stakeholders. For lettuce growers, the project is provided an additional arsenal to combat diseases caused by Sclerotinia species and demonstrated the sustainability of non-chemical approaches over the longer term. This work also provided data on the competitive fitness of Coniothyrium minitans to control S. minor, and improved its efficacy for lettuce drop control. PARTICIPANTS: Dr. BoMing Wu, Oregon State University<br> Steven T. Koike, Farm Advisor, UC Cooperative Extension, Monterey County California Leafy Greens Board<br> Prophyta, Inc. <p> The project also offered postdoctoral training opportunities to Dr. Ravi Chitrampalam. TARGET AUDIENCES: Leafy greens growers in California and Arizona and possibly also New York. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Coniothyrium minitans marketed as Contans has become a standard management tool against Sclerotinia sclerotiorum in a variety of crops including winter lettuce. However, it has been ineffective against lettuce drop caused by S. minor. The interactions between C. minitans and S minor were investigated to determine the most susceptible stage in culture to attack by C. minitans, and to determine its consistency on S minor isolates belonging to four major mycelial compatibility groups (MCGs). Four isolates of S. minor MCG 1 and 5 each from MCGs 2 and 3 and one from MCG4 were treated in culture at purely mycelial, at few immature sclerotial and at fully mature sclerotial phases with a conidial suspension of C. minitans. Sclerotia from all treatments were harvested after 4 wk, air-dried, weighed and plated on PDA for recovery of C. minitans. S. minor formed fewest sclerotia in plates that received C. minitans at mycelial stage, C. minitans was recovered from nearly all sclerotia from this treatment and sclerotial mortality was total. However, the response of MCGs was inconsistent and variable. Field experiments to determine the efficacy of C. minitans relative to the registered fungicide, Endura, on lettuce drop incidence and soil inoculum dynamics were conducted from 2006 to 2009. All Contans treatments had significantly lower numbers of sclerotia than Endura and unsprayed control treatments and drop incidence was as low as (P > 0.05) Endura-treated plots. While the lower levels of lettuce drop in Contans treatments were correlated with significantly lower levels of sclerotia, the lower levels of lettuce drop despite the presence of higher inoculum in the Endura treatment was attributable to the prevention of infection by S. minor. A useful approach to sustained lettuce drop management is to employ Contans to lower the number of sclerotia in soil and to apply Endura to prevent S. minor infection within a cropping season. Funding from the Western Regional IPM provided the resources to conduct laboratory studies on the interactions between C. minitans various genetic populations of S. minor, identify the most appropriate phase of the pathogen for timing the application of the biocontrol treatment, and tested this hypothesis in repeated field experiments. This process of taking the laboratory studies to multi-year field studies made the study very attractive and the outcome of the project so useful to the growers. Many growers have also quickly adapted this treatment in their production fields that have chronic Sclerotinia problem.
Publications
- Chitrampalam, P., Wu, B. M., Koike, S. T., and Subbarao, K. V. 2010. Interactions between Coniothyrium minitans and Sclerotinia minor affect biocontrol efficacy of C. minitans. Phytopathology 100: submitted.
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Progress 07/15/08 to 07/14/09
Outputs
OUTPUTS: The results obtained so far in the project were disseminated by three different avenues to the stakeholders. First, the California Leafy Greens Board conducts two meetings per year to learn of new research developments that would impact the industry. The meetings are held in the central coastal California in March and October each year and are attended by conventional and organic leafy greens growers from throughout California, seed industry representatives, pest control advisors, chemical and biocontrol product industry representatives. The results from the project were presented at these meetings over the past year. Second, the progress in the project over the past year was also summarized in a report to the Leafy Greens Board annual report. Third, an abridged report was also submitted to the biocontrol company representatives. PARTICIPANTS: Ravi Chitrampalam, Barry Pryor, Mike Matheron - University of Arizona California Leafy Greens Board Prophyta, Inc. TARGET AUDIENCES: Leafy greens growers in California and Arizona and possibly also New York. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
The four objectives during the current funding cycle were to: 1) determine the most susceptible stage in the life cycle of S. minor to C. minitans, and optimize conditions for parasitism of S. minor by C. minitans; 2) determine the effects of Contans on production and survival of sclerotia of S. minor; 3) compare Contans with Endura for controlling lettuce drop caused by S. minor in field trials; and 4) continue supporting the breeding program and re-evaluate lines with 'slow-dying' resistance. We conducted laboratory experiments as part of objectives 1 and 2 to determine the most susceptible phase of S. minor for attack by C. minitans. Three isolates of S. minor were challenged at 5, 12 and 22 days after plating with C. minitans. The number of viable sclerotia per plate was then counted for each interaction. Fewest sclerotia formed in S. minor plates that received C. minitans at 5 days in culture. Relative to control (S. minor culture with no C. minitans), C. minitans introduced at 5 and 12 days significantly reduced the number of sclerotia in each plate in all isolates tested. Further studies on the interaction between C. minitans and two isolates of S. minor revealed that C. minitans reduces the number of sclerotia most dramatically in isolates of S. minor that also produce abundant sclerotia but the results were less than impressive for isolates that naturally produce fewer sclerotia. Field studies to evaluate different rates of Contans and different treatment times continued. This year, in addition to the ongoing treatments, two new Contans treatments were introduced in plots that were highly infested with S. minor sclerotia - a single application of Contans just prior to disking the crop residue and application of Contans at thinning and at harvest. Soil was sampled from all treatments after crop emergence and assayed for S. minor sclerotia by wet sieving. Lettuce drop incidence was recorded at weekly intervals until harvest maturity. All Contans treatments had significantly lower numbers of sclerotia in soil relative to the fungicide-sprayed and -unsprayed plots. Lettuce drop incidence in the two Contans treatments applied one week prior to thinning and one week post-thinning was identical to that observed in Endura-applied plots. Since the two new Contans treatments were introduced for the first time in spring 2008, disease levels were not significantly lower than in unsprayed control. However, the Contans treatment applied at thinning and at harvest had the lowest disease in fall 2008. Thus, strategic timing of Contans applications continues to show promise for S. minor control. For lettuce growers, the project is providing an additional arsenal to combat diseases caused by Sclerotinia species. This project is also demonstrating the sustainability of non-chemical approaches over the longer term.
Publications
- Chitrampalam, P., M. E. Matheron, K. V. Subbarao, and B. M. Pryor. 2008. Biocontrol of lettuce drop caused by Sclerotinia sclerotiorum and S. minor in desert agroecosysems. Plant Disease 92:1625-1634.
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