Inducing sporulation of Drechslera graminea

Abstract

Barley stripe, caused by the fungus Pyrenophora graminea, is a single-cycle, seedborne disease. P. graminea is rarely observed in the nature, but its imperfect state, Drechslera graminea, occurs in all infected barley leaves. D. graminea produces conidia, which are in clusters of three to five. The fungus can also produce pycnidia, but it is rare in nature. Although barley stripe is effectively managed by seed-treatment with fungicides, losses to this disease still incurs wherever proper seed treatment is not practiced. D. graminea does not sporulate on commonly used artificial culture media. Therefore, production of spores to be used for screening accessions and breeding lines of barley for resistance to barley strip was not possible. A simple method was developed to induce sporulation in D. graminea. Thirty-six isolates of D. graminea, gathered from Canada, Germany, Montana and Syria, were cultured, developed vigorous colonies and produced abundant conidia. Sporulation of the fungus was induced using straw extract from the barley cultivars arta, bowman, bracken, clark, gallatin, and salmas. There were significant differences in sporulation among isolates from different areas as well as among isolates originating from the same barley field. Incubating the culture plates at 160C under fluorescent light (12 h light/12 h dark) for 5 d following incubation under near ultraviolet (NUV) light for 7 d resulted in 40% higher conidia production. Extract of seed, green straw or green leaves of barley as well as extract of mature wheat straw did not induce sporulation in D. graminea in culture. Twenty-one of the 36 isolates produced pycnidia following the 7-day incubation under NUV light. Five of 25 isolates grown on V8juice agar failed to sporulate. Germination of conidia of 12 isolates ranged from 72 to 99%.