Pathogenicity and Characterization of Geographically Distributed Isolates of Erysiphe polygoni

Abstract

The incidence of powdery mildew disease on pea (Pisum sativum L.) is a major limiting factor to maximizing yields in different ecological and geographical zones due to environmental factors and the presence of pathogenic variation in Erysiphe polygoni DC. In order to develop a widely adopted powdery mildew–resistant cultivar it is necessary to challenge genotypes with all available pathogenic variants. In order to examine pathogenic variation, 23 naturally occurring single colony isolates of E. polygoni, collected from geographically diverse locations, were subjected to pathogenicity testing and characterization using a detached leaf assay. Isolates demonstrated small differences in pathogenicity against pea. Isolates MUZ-1 and MUZ-2 were the most virulent and produced disease symptoms even on the resistant cultivars. Isolates TTS-2 and TTS-6 were less virulent. Significant variation occurred among isolates for quantitative and qualitative parameters regardless of the degree of pathogenicity. There was variation for conidium length, conidium width, cleistothecia number, number of hyphae, ascus number, ascus length, ascospore number, and ascospore width. An unweighted pair group method with arithmetic mean phenogram, constructed on the basis of quantitative parameters, indicated that isolates were morphologically different but pathogenicity was not controlled by morphological features of the isolates, though morphological features can be used to distinguish between isolates.

Keywords:

• Pisum sativum
• Cluster analysis
• Detached leaf assay
• Disease scoring
• Pathogenic variation
• Powdery mildew