STUDIES ON LEPTOSPHAERIA AVENARIA f. sp. AVENARIA

Abstract

Pycnidiospores assignable to Septoria avenae Frank and asci and ascospores assignable to Leptosphaeria avenaria Weber were isolated from cereals and grasses in Canada, but studies herein reported concern only oat-infecting isolates. Macrospores of the oat-infecting organism occurred on green and mature oats during the summer, on oat stubble in the early autumn, and occasionally on old stubble in spring. Microspores were found on mature oats and stubble at the end of August; they occurred abundantly on stubble throughout the winter, and were still present on a few collections in May and June. Immature perithecia were found on stubble in April and perithecia with mature ascospores on June 16, but stubble moistened in the laboratory before that date had discharged mature ascospores.Cultures derived from macro-, micro-, and asco-spores produced macro- and micro-spores in culture; of the 82 cultures derived from single ascospores all except seven formed pycnidia and macrospores, and of the 100 cultures derived from single microspores, all except four formed macrospores. No perithecia were found in culture on various media undar different conditions, or when isolates were paired in various combinations. The macrospores and ascospores have one nucleus per cell, the nuclei of each spore originating from one nucleus. Microspores are uninucleate.Newly discharged ascospores germinated in about 1 hour and macrospores in a few hours in water. Microspores took at least 40 hours to germinate on solid media.In culture, low temperature favored microspore formation and high temperature macrospore formation. Microspores were also found in cultures of Septoria nodorum and S. oudemansii, but not in cultures of L. avenaria f. sp. triticea.The means of overwintering of the organism are discussed; it is considered that, although macro- and micro-spores are available in the spring, ascospores are probably the principal spring inoculum.Oat-infecting isolates did not infect the other cereals or certain grasses, and the oat-infecting isolates were obtained only from oats. The International Rules of Botanical Nomenclature are interpreted to mean that with the erection of the f. sp. triticea, the type automatically becomes L. avenaria f, sp. avenaria (imperfect S. avenae f. sp. avenae).