Brown rust (Puccinia melanocephala), first reported in Tucuman in 1988, and orange rust (P. kuehnii), not yet reported in Argentina, cause important yield loss in global sugarcane production. Due to the difficulties of distinguishing between the two diseases in sugarcane to the naked eye, it is essential to use molecular techniques for an accurate rust diagnosis. A major gene, Brul, 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 to this allele have been developed. It is the aim of the present study i) to optimise a PCR-based method in order to diagnose and characterise the causal agent population of both types of rust in Tucuman; ii) to determine the usefulness of the Bru 1 gene in the Sugarcane Breeding Program of 'Estacion Experimental Agroindustrial Obispo Colombres' (EEAOC) by studying its association with resistant and susceptible phenotypes; and iii) to assess the frequency of the Bru 1 allele in the sugarcane germplasm of the EEAOC. Conditions for both brown and orange rust diagnosis were optimised. When analysing thirty samples of sugarcane showing rust symptoms, only DNA from P. melanocephala was amplified. Sugarcane varieties frequently used in the EEAOC Breeding Program were analysed in order to study the usefulness of the Bru 1 allele to diagnose brown rust resistance in Tucuman. Out of 129 genotypes evaluated, 49 (38%) were found to be resistant to brown rust but only 8 (16.3%) of these resistant genotypes were positive for the Bm\ allele. We then analysed the frequency of appearance of the Bru\ allele by using diagnostic markers, R12H16 and 9020-F4-Rsal, in 191 sugarcane accessions of the EEAOC germplasm. Presence, as determined by the two markers, was detected in only 7% of the genotypes evaluated. Although results show that Bru 1 markers enable positive selection of this character, additional source(s) of resistance are available in