COMPARISON OF FIVE ISOLATES OF SUGARCANE BROWN RUST AND DIFFERENTIAL REACTION ON SIX SUGARCANE CLONES

摘要

The OCCURRENCE of pathological races of sugarcane brown rust (Puccinia melanocephala H. and P. Sydow) in Florida was first reported in 1984. Cultivars that were resistant to the disease in the variety development program displayed susceptibility to the disease once expanded commercially. A study was conducted over two years to determine the effect on yield of six cultivars of sugarcane to five isolates of the sugarcane rust pathogen suspected to be differing pathological races. Sugarcane plants were grown in pots and inoculated under conditions favouring disease development while preventing infection of non-inoculated control plants. Plant height, estimates of percent infection and whole-plant disease ratings were recorded bi-weekly for 4 months during the late winter and spring of 1991 and 1992. Final plant height and fresh weight were measured at the end of the experiment each year. Areas under the disease progress curves (AUDPC) for plant height, percent infection and disease rating were calculated. Analysis of variance and single-degree-of-freedom comparisons were used to interpret results for all response variables. These analyses indicated the existence of four pathogenic races of the brown rust pathogen in this experiment. These data coupled with field observations lead to the hypothesis that pathogenic variants of P. melanocephala develop within the sugarcane production region and parallel the development of new commercial sugarcane cultivars. The diversification of commercial cultivars and identification of horizontal resistance mechanisms will reduce losses to sugarcane brown rust in the Florida sugarcane industry.