Pea black spot disease complex on field pea: dissecting the roles of the different pathogens in causing epicotyl and root disease

Abstract

This study aimed to determine the relative importance of three well recognized devastating pathogens of field pea (Pisum sativum) on leaves and stems, Didymella pinodes, Phoma pinodella and P. koolunga, in also causing disease on epicotyls and roots. Two pea varieties, Kaspa and WAPEA2211, were inoculated with four isolates of each pathogen; subsequently epicotyl and root disease were scored accordingly. All pathogens caused epicotyl and root disease. D. pinodes isolates caused consistently severe disease on epicotyl, lateral root and tap root. Except for variable levels of disease on epicotyls, P. pinodella isolates also caused consistently high levels of disease on lateral and tap roots. While P. koolunga, generally caused less epicotyl and root disease than D. pinodes and P. pinodella, some isolates of P. koolunga caused severe tap root rot. For example, on WAPEA2211, P. koolunga (isolates#1 and #3) caused similar levels of tap root rot as with the two most virulent isolates of D. pinodes and as with the treatment with the three pathogens combined. The three pathogens combined treatment caused particularly severe disease on epicotyls, lateral and tap roots. For the first time, P. koolunga was shown to cause epicotyl and root disease on field pea, but less severe than the other two pathogens tested. Findings of this study highlight, for the first time, the relative roles of these three black spot pathogens, particularly P. koolunga; demonstrate a much wider and more significant adverse impact of the black spot complex than assumed historically; and underscore the additional challenges posed for pea breeders in developing black spot all-inclusive resistant varieties.