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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research Unit » Research » Publications at this Location » Publication #304243
Title: Development of a grower performed inoculum detection assay for management of grape powdery mildew

Author
item THIESSEN, LINDSEY - Oregon State University
item KEUNE, JESSICA - Oregon State University
item Neill, Tara
item Turechek, William
item GROVE, GARY - Washington State University Extension Service
item Mahaffee, Walter - Walt

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2015
Publication Date: 6/26/2015
Citation: Thiessen, L.D., Keune, J.A., Neill, T.M., Turechek, W., Grove, G., Mahaffee, W.F. 2015. Development of a grower performed inoculum detection assay for management of grape powdery mildew. Plant Pathology. 65:238–249. doi: 10.1111/ppa.12421

Interpretive Summary: Current management of grape powdery mildew is based on the assumption that inoculum is available from the time susceptible plant tissue is available. We have demonstrated that growers can save >2 fungicide applications per year without reducing disease control by initiating their fungicide applications when airborne spores of the pathogen are detected in the air. We then developed a detection assay that can be used by growers in their facilities that was as accurate as the expensive laboratory assays.

Technical Abstract: Management of grape powdery mildew (Erysiphe necator) and other polycyclic diseases relies on calendar-based pesticide application schedules. However, these schedules may be adjusted to optimize and often reduce the number of applications by utilizing information generated from infection risk forecasts from local or regional weather data. This approach does not account for asynchronous pathogen-host development that may be an important consideration in optimizing fungicide applications. An inexpensive, loop-mediated isothermal amplification (LAMP) assay was developed to detect the presence of airborne E. necator inoculum suitable for growers to perform and to inform decisions on when to initiate fungicide application program. Field efficacy was tested in 2010 and 2011 by placing three continuously-running, rotating arm impaction traps in several commercial and research vineyards within the Willamette Valley of Oregon from mid-March to véraison. One trap was maintained and used by the grower to conduct the LAMP assay on site and the other two traps used for laboratory conducted LAMP (L-LAMP) and quantitative PCR (qPCR) assays. Using the qPCR assay as a gold standard, L-LAMP was comparable with the qPCR assay in both years, and the grower-conducted LAMP (G-LAMP) was comparable to the qPCR assay in 2011. Latent class analysis indicated that the qPCR assay was sensitive (98% in 2010 and 89% in 2011) and specific (96% in 2010 and 64% in 2011) while the L-LAMP and G-LAMP were less sensitive (85% and 61%) and specific (99% and 98%), respectively in 2011. However, despite the reduce sensitivity and specificity; there was no difference in the management decisions made using the G-LAMP assay. An average of 3.25 fungicide applications were saved when the fungicide applications were initiated based on detection compared to the grower standard with no significant differences in berry or leaf incidence between managed and control plots, indicating that utilizing LAMP inoculum detection for initiating fungicide applications was as successful as the grower standard practices in