DETECTION OF POWDERY MILDEW IN GRAPES USING A DNA ASSAY AND NEAR INFRARED REFLECTANCE SPECTROSCOPY, AND ASSESSMENT OF CHARDONNAY WINE QUALITY

The E. necator-specific DNA clone detected the pathogen in grapes, must and juice. Compared with visual assessment, the E. necator-specific DNA probe provides a reliable and objective means of detecting and quantifying powdery mildew in grapes, juice and must. The detection threshold is approximately 100 conidia. NIR could discriminate the least infection category from uninfected samples, but these samples were from a small number of trial plots. To ensure a robust calibration, further material representing more diversity must be scanned. Even small amounts of powdery mildew, as little as 1-5% of the bunch infected, resulted in increased oily, viscous mouth-feel characters. The detection tools described here offer the grape industry a means of obtaining objective, quantitative data on disease severity in grapes, must and juice samples at the winery, particularly when disease is slight and visual assessment is difficult. Such information can then be used to inform decisions about the use of grapes and must to achieve desired outcomes.