Abstract

RACEDO, Josefina et al. Molecular diagnostic of both brown and orange sugarcane rust and evaluation of sugarcane brown rust resistance in Tucumán- Argentina using molecular markers associated to Bru1, a broad-range resistance allele. Rev. ind. agric. Tucumán [online]. 2014, vol.91, n.1, pp.47-53. ISSN 1851-3018.

Brown rust (Puccinia melanocephala), first reported in Tucumán in 1988, and orange rust (P. kuehnii), not yet reported in Argentina, cause important yield losses in global sugarcane production. Due to the difficulties in distinguishing these two sugarcane diseases with the naked eye, it is essential to use molecular techniques for an accurate 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 present study aims to i) optimise a PCR-based method to diagnose and characterise the causal agent population of both types of rust in Tucumán; ii) 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 iii) assess the frequency of the Bru1 allele in EEAOC sugarcane germplasm. Conditions for both brown and orange rust diagnosis were optimised. When analysing 30 sugarcane samples showing rust symptoms, only P. melanocephala DNA was amplified. Sugarcane varieties frequently used in the EEAOC Breeding Program were analysed in order to study the usefulness of the Bru1 allele to diagnose brown rust resistance in Tucumán. Out of 129 evaluated genotypes, 49 (38.0%) were found to be resistant to brown rust, but only 8 (16.3%) of these were positive for the Bru1 allele. We then analysed the frequency of appearance of the Bru1 allele by using diagnostic markers R12H16 and 9020-F4-RsaI, in 191 sugarcane accessions of the EEAOC germplasm. Presence, as determined by the two markers, was detected in only 7% of the evaluated genotypes. In conclusion, although results showed that Bru1 markers enable positive selection of this character, additional resistance source(s) are available in the EEAOC Sugarcane Breeding Program.

Keywords : Marker assisted selection; Puccinia melanocephala; Puccinia kuehnii.

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