Molecular Diagnostic of Both Brown and Orange Sugarcane Rust and Evaluation of Sugarcane Brown Rust Resistance in Tucuman, Argentina, Using Molecular Markers Associated with Bru1 a Broad-Range Resistance Allele

Abstract

Brown rust (Puccinia melanocephala) and orange rust (P. kuehnii) cause important yield loss in global sugarcane production. Due to the difficulties of distinguishing between the two diseases to the naked eye, it is essential to use molecular techniques for an accurate rust diagnosis. A major gene, Bru1, which confers resistance to a broad spectrum of P.melanocephala strains in different parts of the world, has been described, and molecular markers closely associated with this allele have been developed. The aims of the present study were: (1) to optimise a PCR-based method to diagnose and characterise the causal agent of both rusts in Tucumán; (2) to determine the usefulness of the Bru1 gene in the Sugarcane Breeding Program of “Estación Experimental Agroindustrial Obispo Colombres” (EEAOC) by studying its association with resistant and susceptible phenotypes; and (3) to assess the frequency of the Bru1 allele in the sugarcane germplasm of the EEAOC. Conditions for both rust diagnoses were optimised. Out of 129 genotypes evaluated to study the usefulness of the Bru1 allele, 49 were found to be resistant to brown rust, but only eight of these resistant genotypes were positive for the Bru1 allele. Also frequency of appearance of the Bru1 allele was analysed in 191 sugarcane accessions of the EEAOC germplasm, and its presence was detected in only 7 % of the genotypes evaluated. In conclusion, although results showed that Bru1 markers enable positive selection of this character, additional source(s) of resistance are available in the EEAOC Sugarcane Breeding Program.