Reaction to Brown Rust and Presence of the Bru1 Gene in Brazil/RIDESA Sugarcane Parents

Brown rust is an important disease that can affect the production of sugarcane in susceptible varieties. Reaction to brown rust has influenced the improvement programs in the process of clonal selection. Bru1 is one of the main resistance genes for brown rust. Therefore, the knowledge of the reaction to brown rust in the genotypes most used as parents in hybridizations would avoid crosses between susceptible genotypes. In this sense, the objectives of this work were to evaluate the reaction to brown rust in the field and the pattern of disease evolution; and the presence of the Bru1 gene in sugarcane parents of the RIDESA genetic improvement program. The experiment was carried out at the Paranavai experimental station, where 64 genotypes were planted in a randomized block design with three replications. The severity of brown rust in the field under natural infection conditions and the presence of the Bru1 gene were evaluated. Of the 63 genotypes evaluated, 38 were classified as resistant, 13 as intermediate and 12 as susceptible. Lower values of severity of brown rust were observed in intermediate genotypes with a slow evolution of the disease when compared with susceptible parents, indicating a quantitative resistance. Bru1 was detected in 58.7% of the evaluated genotypes. The frequency of Bru1 increased from 0% in the genotypes used as parents in the 1970s to 20, 64.71 and 76% in the 1980, 1990 and 2000s, respectively.