Evidence for the existence of a single race of common rust caused by Puccinia melanocephala, in Australian sugar cane cultivars

Abstract

A detached-leaf method for testing for physiological races of common rust disease, caused by Puccinia melanocephala, in Australian sugar cane cultivars is described. Single-uredium isolates collected from various locations in Queensland, Australia, between 1978 and 1986 were screened. Host reaction type was specific to individual cultivars and did not vary when these cultivars were inoculated with different rust isolates. For each cultivar there was no difference in generation time for each isolate. These results suggest that there is only one physiological race present in the pathogen population in Queensland. Reported changes in the severity of common rust disease in sugarcane cultivars were caused by changes in environmental conditions rather than the development of new races of the pathogen. Rust infection fluctuated during the growth of sugar cane, with a major peak occurring at tillering and stem elongation, following moderate rainfall and temperatures between 12 and 25¦C. Rust was more severe on older leaves than on younger leaves.