Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2006
Publication Date: 4/23/2007
Citation: Falacy, J. S., Grove, G. G., Mahaffee, W. F., Galloway, H., Glawe, D. A., Larsen, R. C., and Vandermark, G. J. 2007. Detection of Erysiphe necator in air samples using the polymerase chain reaction and species-specific primers. Phytopathology 97:1290-1297.
Interpretive Summary: This research was conducted to develop a more accurate and efficient method for determining the presence of grape powdery mildew in vineyards. Using the polymerase chain reaction and primers (pieces of DNA) that are specific for E. necator, it was possible to detect as few as one spore without cross reacting with other powdery mildews common to plants located within and around vineyards. The system was sucessful in detecting the intiation of the disease epidemic in vineyards in 2004 and 2005 that corresponded with the known epidemiology of E. necator. Results from these studies indicated that growers could have delayed their disease control program in each year by 3-4 weeks which would have resulted in the saving of two pesticide applications.
Technical Abstract: A polymerase chain reaction (PCR) assay employing species-specific primers was developed to differentiate Erysiphe necator (Uncinula necator) from other powdery mildews common in the northwest United States. DNA was extracted from mycelia, conidia, and/or cleistothecia that were collected from grape leaves using a Burkard cyclonic surface sampler. To differentiate E. necator from other erysiphaeceous fungi, primer pairs Uncin144 and Uncin511 were developed to select unique regions of the internal transcribed spacer (ITS) regions of E. necator. The primers and PCR generated a 367 bp amplicon specific from E. necator, but did not generate amplicons from other erysiphaceous species collected from 46 disparate hosts representing 26 vascular plant families. The PCR assay was able to detect one to five conidia of E. necator placed in reaction mixtures or 500 conidia placed on silicon grease coated glass rods. This PCR assay facilitated the detection of low levels of E. necator inoculum in air samples within hours of collection during greenhouse and field studies prior to disease onset. Amplification of E. necator did not occur during grape dormancy. The intial PCR detection of E. necator occurred during ascospore releases hastened by precipitation events between bud burst and the prebloom period during both years of the study. Detection then eased for 7-10 days following ascospore releases and then resumed several days prior to the observance of microscopic symptoms and signs of powdery mildew. Results of this study should represent the initial step in the incorporation of an inoculum availability component into current and future grapevine powdery mildew risk assessment models.