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.* Y CASTAGNARO, A. P.*

Congreso; ISSCT CONGRESS; 2013

Brown rust (Puccinia melanocephala), present in Tucumán since 1988, and orange rust (P. kuehnii), not yet reported in Argentina, cause important yield loss in global sugarcane production. Due to the difficulty of distinguishing between these two diseases by visual observation, it is essential to use molecular techniques in order to diagnose rust symptoms correctly. 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 have been closely associated with the resistance allele. Our work aimed to i) optimize molecular methods for diagnosis, characterization and population analysis of P. melanocephala and P. kuehnii and ii) assess the presence of markers associated with Bru1 in our local breeding program germplasm. Thirty samples of sugarcane leaves with rust symptoms and leaf samples from 251 sugarcane genotypes were collected. Conditions for nucleic acid extraction and amplification of rDNA with five pairs of primers for diagnosis were optimized. All samples showing rust symptoms were positive for P. melanocephala, as they amplified fragments of 670 bp (ITS1F/ITS4), 608 bp (NL1/NL4), 585 bp (PkPmF/PkPmR) and 480 bp (Pm1F/Pm1R). No amplification of DNA was observed when the primer pair specific for P. kuehnii was used. These molecular protocols for P. melanocephala and P. kuehnii constitute robust and specific diagnostic tools available to local growers. Fifteen out of the 251 genotypes analized for Bru1 associated markers were positive. Correlation between marker presence and resistance to the disease has been determined. This enables an novel early, rapid and positive selection for this character in our sugar cane breeding programs.