Diversity in the effect of an extract from Fallopia sachalinensis on isolates of cucurbit powdery mildews grown on melon

Abstract: Powdery mildew caused by Podosphaera xanthii and Golovinomyces cichoracearumis one of the principal diseases on cucurbit crops in temperate climates. In order to control thisdisease, various biological methods, including induced resistance by the use of extracts fromFallopia sachalinensis, have been identified. This study was conducted to characterise thediversity of susceptibility to this plant extract among 52 isolates of P. xanthii and 5 isolates of G.cichoracearum collected from various cucurbit species in different production areas. To this end,disks excised from melon leaves were soaked in a preparation of F. sachalinensis extract (1%w/v) or in a control solution, inoculated with fresh conidia of powdery mildew 24 hours aftertreatment and placed in a growth chamber. Ten days after inoculation, symptoms were rated inclasses based on a visual estimation of the leaf area infested by powdery mildew. Additionally,spore production on the leaf disks was assessed. The plant extract significantly decreased theseverity of disease for all the powdery mildew isolates tested. On average, spore production wasonly ca. 20% in presence of the plant extract relative to the untreated control. However, theextent of the reduction in spore production varied widely among isolates.