The epidemiology of yellow spot of wheat in southern Queensland

Abstract

Aspects of the epidemiology of yellow spot of wheat, caused by Pyrenophovu tritici-repentis, have been examined in southern Queensland. Ascospores of the fungus were detected In the air above wheat stubble between March and October, but numbers at any one time were small. Small numbers of conidia trapped between late February and May apparently originated on the stubble. Large numbers of conidia in late October-November were produced predominantly on old lesions and dead tissues in a wheat crop planted through the stubble During late spring, numbers of air-borne conidia increased markedly the day after rain or irrigation. The results suggest that epidemics of yellow spot in southern Queensland are mainly initiated by ascospores and possibly conidia produced on stubble from the preceding diseased wheat crop. Large numbers of conidia produced on a diseased crop result in rapid development of the epidemic under favourable conditions and permit spread of the pathogen to other crops or localities.