In its 2021-22 fiscal year, the Oregon Wine Board of Directors granted $289,000 to researchers for six projects with the potential to advance quality grape growing and winemaking in Oregon. The update below is part of a series to let industry members know about the status of these projects.
Walt Mahaffee, Research Plant Pathologist in the Horticultural Crops Disease and Pest Management Research Unit at the USDA-ARS, and Alexander Wong, Graduate Research Assistant at Oregon State University Department of Botany and Plant Pathology, are the principal investigators on the project. Cooperators include Virginia Stockwell, Research Plant Pathologist in the Horticultural Crops Disease and Pest Management Research Unit at the USDA-ARS, and Rachel Naegele, Research Geneticist, USDA-ARS SBBRU.
Botrytis Bunch Rot: Who, Where, When, And What to Use
1. Characterize fungicide tolerance of Botrytis isolates from vineyards
2. Monitor potential sources of inoculum in and around vineyards.
3. Monitor inoculum levels throughout the growing season.
Importance to the Oregon wine community:
Grape bunch rot (Botrytis spp.) is an important grape pathogen that can greatly affect crop quality. This causes to vineyards with bunch rot issues to rely heavily on fungicide applications, which in turn, increases the risk of fungicide tolerance emergence. The outcome from the project will improve on how bunch rot is controlled to manage and mitigate the development of fungicide resistance. To achieve this outcome, we need to advance our understanding of Botrytis epidemiology. Combining this with a survey of fungicide tolerance of Botrytis will allow for the development rational mitigation approaches to managing disease pressure and fungicide tolerant populations of Botrytis.
Progress so far:
In 2020 and 2021, nine and eleven vineyards, respectively, in the Willamette Valley, Oregon were sampled for Botrytis from June to September. Grape clusters, vineyard floor grapevine debris (rachis), and nearby wild blackberries were collected, incubated, and visually assessed for Botrytis. Bunch rot incidence on clusters throughout the field season ranged from about 3% to over 30% in 2020 and around 1% to 11% in 2021. Botrytis incidence on vineyard floor debris in 2021 decreased as the season progressed in all but one location having greater than 75% in late April and under 25% by September. For field sites where wild blackberries were present, Botrytis on blackberry flower parts and berries was found at low levels throughout the season. Botrytis isolates generated from these grape, debris, and blackberry samples were screened for fungicide tolerance to Benomyl (FRAC 1), Iprodione (FRAC 2), Difenoconazole, Myclobutanil, Tebuconazole (FRAC 3), Boscalid, Fluopyram (FRAC 7), Cyprodinil (FRAC 9), Azoxystrobin and Trifloxystrobin (FRAC 11), Fenhexamid (FRAC 17), and Polyoxin-D (FRAC 19). There was some level of tolerance to all fungicide classes tested, with tolerance to more than one fungicide class observed in 26% of the >200 total isolates tested so far. Airborne Botrytis conidia from impaction spore traps were assessed from April to September by qPCR assays. Spore trap qPCR assays have shown that there can be surges of conidia being released during grapevine bloom when temperatures (15-25°C) and humidity (>70%) are favorable. These results taken together suggest that fungicide tolerance levels of vineyard Botrytis are of concern and should continue to be monitored, along with the seasonal and environmental changes of Botrytis inoculum to better time applications of fungicides and other integrative pest management tools.
These results indicate that botryticide modes of action should be only used once a season due to presence resistance to most current modes of action and applications should be focused around bloom, when inoculum is most prevalent, and the environment is favorable for colonization of susceptible host tissues.
The above results from 2020 and 2021 collections are available online with the qPCR results of airborne inoculum trends to be published by August 2022. The next steps of the project will be continuing to sample sites for Botrytis in 2022, characterizing isolates for fungicide tolerance, and tracking inoculum trends using qPCR assays. Results will be published online when they become available.
This project also received funding from the Northwest Center for Small Fruits Research