Molecular Markers Associated with Brown Rust Resistance in a Sugarcane Bi-Parental Cross

Sugarcane crop is economically important because is the main source of sugar and alcohol. The global sugar forecast overview for 2013/14, ranked Brazil on a record in production, with 40.4 million tons, up 1.8 million on higher yields as result of good weather and adequate sugarcane renewal. However, production can be improved as development of new sugarcane brown rust resistant clones. Brown rust is caused by Puccinia melanocephala, being the most studied sugarcane disease and has been responsible for important yield losses around the world. Bru1 is known as the major gene conferring resistance to brown rust in sugarcane. Four markers linked to Bru1 (m164H22-PCR, cBr37-PCR, R12H16-PCR and 9020-F4-PCR-RsaI) were obtained from public domain. Genotyping was performed through qPCR and analyzed according to presence or absence of amplified fragment. A total of 241 individuals of a bi-parental commercial cross were used (SP81-3250-resistant x RB925345-susceptible). Field evaluation was conducted in two locations, with three replications. Results showed that m164H22-PCR marker was nuliplex, while the cBr37-PCR, R12H16-PCR and 9020-F4-PCR-RsaI markers were segregating according to 1:1 Mendelian proportion, which is a strong evidence of single dose. In general, all individuals (97.5%) phenotyped as resistant had presence of at least one marker of Bru1, with high heritability (0.85). This result shows that the PCR diagnostic using Bru1-based markers is a powerful strategy to identify resistant cultivars to brown rust, and easily applied to sugarcane breeding program.