Reaction of sugarcane varieties to orange rust (Puccinia kuehnii) and methods for rapid identification of resistant genotypes

摘要

Sugarcane orange rust was recently introduced into Brazil and its control is based on the use of resistant varieties. This study aimed to determine the reaction of Brazilian sugarcane varieties to the disease in the field and to compare artificial inoculation methods. Rust severity was assessed in 17 varieties at a 15-day interval. The maximum disease severity (MS%) and the area under the disease progress curve (AUDPC) were determined for each genotype. The artificial inoculation methods tested were: spraying of a spore suspension on 60-day-old plants in the greenhouse, or placing the spore suspension into the leaf whorl of 5-month-old field-grown plants. Nine out of the 17 varieties studied were resistant to the disease, including the most widely grown in new plantings, RB867515 and RB966928. Varieties RB72454, SP89-1115 and SP79-2233 were susceptible, while RB925211 and SP81-3250 were moderately susceptible. Varieties RB855156, RB92579 and SP83-2847 showed an intermediate reaction. Both inoculation methods correlated well with field results. Spray inoculation discriminates better the responses of the varieties and enables the evaluation of more disease variables. Leaf whorl inoculation allows the use of field-grown plants and generates results in a shorter time.