A species of Unguicularia on oilseed rape, and its importance in studies of the epidemiology of light leaf spot (Pyrenopeziza brassicae)

Abstract

Apothecia of a species of Unguicularia were found on fallen leaves of oilseed rape from November 1989 to April 1990, and from January to July 1991. On the basis of the limited literature on this genus, these apothecia were tentatively identified as Unguicularia cfr. raripila, a species not previously reported in the UK, or on oilseed rape. Although saprophytic, it is of significance in oilseed rape crops, as its ascospores are similar in size and shape to those of the important pathogen Pyrenopeziza brassicae, the cause of light leaf spot. The ascospores of both species can be dispersed either as single spores or in groups, although those of U. cfr. raripila are more often dispersed in groups. Due to confusion in distinguishing the ascospores of these two species, it is likely that studies of the epidemiology of light leaf spot using spore samplers have overestimated the numbers of ascospores of P. brassicae dispersed, and hence their potential contribution to epidemics. Apothecia of U. cfr. raripila were abundant in the spring of both 1990 and 1991, but those of P. brassicae were much more rare. The species of Unguicularia is described.