Development and evaluation of detection-based air sampling programs for grapevine powdery mildew

Laura Costadone

Powdery mildew of wine grape (Vitis vinifera L.), caused by Erysiphe necator, is one of the most problematic diseases of grapevine worldwide. A real-time PCR assay using species-specific primers was developed for qualitative and quantitative detection of E necator in vineyard air samples collected by Rotorod sampling devices. Three methods (FastPrep DNA kit, UltraClean MoBio and FastPrep DNA kit for soil) were used to purify DNA of E. necator collected from air samples and evaluated with respect to conidia DNA yields. The DNA yields varied considerably with the extraction procedure used. Results of this study suggest that the less sensitive FastPrep method can at times fail to detect the presence of the pathogen in the air, possibly due to high presence of PCR inhibitors such as dust and soil particles in the Rotorod samples. The false-negative results are of concern when knowledge of the inoculum presence and viability could be useful in determining the initiation of disease management programs. Fungicide treatments may not be initiated or erroneously discontinued if the pathogen is presumed absent or inactive by a false-negative result. Our results show that DNA quantification was closely correlated with the quantity of spores monitored with Burkard volumetric spore traps, the disease severity assessed in the vineyard and some weather parameters measured within and outside the vineyard. A high degree of correlation was observed between the airborne conidia concentration monitored by the Burkard trap and the DNA concentration extracted from the Rotorod samples, demonstrating the potential of both type of samplers, used in a complementary way, to accurately quantify pathogen occurrence in environmental samples. The findings of this study describe a rapid, reliable method to assess the presence or absence of the pathogen and the initial step in incorporating an inoculum component in the powdery mildew risk assessment model in widespread use in Eastern Washington. The technique could be used as a means to signal the commencement of fungicide applications. In this regard, the application of control methods would be due to pathogen activity, rather than predicted or assumed activity.

Development and evaluation of detection-based air sampling programs for grapevine powdery mildew

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