Molecular diagnostics of Puccinia melanocephala and Puccinia kuehnii causing agents of brown rust and orange rust, respectively and evaluation of rust resistance in the EEAOC germplasm collection using molecular markers associated to Bru1 a broad-range re

RACEDO J.; PERERA M.F.; BERTANI R.; FUNES C., GONZÁLEZ V.; CUENYA M. I.; D´HONT A.; WELIN B. AND CASTAGNARO, A. P.

Congreso; XXVIII ISSCT Congress; 2013

Brown rust (Puccinia melanocephala), first reported in Tucumán 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, 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 to this allele have been developed. It is the aim of the present study i) to optimize a PCR-based method in order to diagnose and characterize the causal agent population of both types of rust in Tucumán; ii) 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 iii) to assess the frequency of the Bru1 allele in the sugarcane germplasm of the EEAOC. Conditions for both brown and orange rust diagnosis were optimized. When analyzing thirty samples of sugarcane showing rust symptoms, only DNA from P. melanocephala was amplified. Sugarcane varieties frequently used in the EEAOC Breeding Program were analyzed in order to study the usefulness of the Bru1 allele to diagnose brown rust resistance in Tucumán. 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 Bru1 allele. We then analyzed 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 genotypes evaluated. In conclusion, although results show that Bru1 markers enable positive selection of this character, additional source of resistance are available in EEAOC Sugarcane Breeding Program.