The Survival and Control of Pyrenophora Avenae Ito & Kuribayasi and Associated Micro-Organisms Carried on Stored New Zealand Seed Oats

Abstract

The seed-borne microbial flora of 93 samples of New Zealand seed oats, which were stored for periods of up to seven years was studied by the Ulster Method. Fungi belonging to twenty-one genera, one genus of bacteria and one genus of actinomycete were identified. Among the non-pathogens, Alternaria tenuis auct., Mucor sp., Penicillium sp., Rhizopus sp. were the most frequently isolated. Eighty-nine percent of the sample tested was infected with the pathogen Helminthosporium avenae Eidam, which was still detected in seeds stored up to seven years. Fusarium species were detected only in seed from the 1971 harvest; Ustilago spores were present in seeds stored for six years but it is not known whether they are still viable. However, bacterial colonies still emerged from seeds stored for seven years. Seed ageing was discounted as an alternative control measure to seed dressing for P. avenae. The dominant pathogen differed according to cultivar in seed harvested in 1971. The cultivar Mapua carried the highest infection of H. avenae; Amuri, the highest Fusarium infection; Black, the most Ustilago spores per kernel and Algerian, the highest bacterial infection. In addition to P. avenae, mercury-resistant strains of Fusarium poae (Peck.) WR., Chaetomium sp., Epicoccum nigrum (Link) Schol-Schwarz, Phoma sp. and bacteria were detected. Four Fusarium species are described: F. avenaceum (Fr.) Sacc., F. culmorum (W. G. Smith) Sacc., F. poae (Pk.) WR., and F. sp.