The effects of different biological control agents (BCAs) and plant defence elicitors on cucumber powdery mildew (Podosphaera xanthii)

Abstract

An experiment was conducted in both 2008 and 2009 to develop and evaluate strategies for the control of cucumber powdery mildew caused by Podosphaera xanthii. Effects of biological control agents (BCAs) Ampelomyces quisqualis and Pythium oligandrum and plant defence elicitors Milsana® VP 2002 (a plant extract of Reynoutria sachalinensis) and chitosan (derived from chitin) alone and in combination on disease incidence and fruit yield of two cucumber cultivars were investigated. As the cultivars Gloria and Palmera differed in their tolerance to powdery mildew it was possible to test if the use of tolerant cultivars could maximise any beneficial effects of the treatments. In both cultivars in both years, the elicitor Milsana® VP 2002 reduced the disease incidence and fruit yield was similar to that from plants treated with the chemosynthetic fungicide treatments. Whilst foliar application of the other elicitor chitosan significantly reduced powdery mildew, it was less effective than Milsana® VP 2002. BCAs A. quisqualis and P. oligandrum were less effective than the elicitors Milsana® VP 2002 and chitosan and fruit yield was similar to untreated control plants. There was no synergistic or additive effects on disease control or fruit yield detected with any combinations. Disease tolerance of cultivars significantly affected disease incidence. However, the more susceptible cultivar Palmera outyielded the tolerant one (Gloria) despite greater infection.