Assessing tolerance to soybean rust in selected genotypes

Breeding for tolerance to soybean rust is potentially one of the solutions to combating soybean rust; however, very little progress in tolerance breeding has been documented. Fourteen pre-selected genotypes were evaluated in a sprayed versus unsprayed split-plot trial conducted over three seasons for their tolerance to soybean rust. Different assessments of tolerance were compared for their effectiveness in discriminating between genotypes. Conventional methodology using a yield loss % index for assessing tolerance produced results which were poorly correlated with each other over seasons, which likely accounts for the historic lack of breeding success. This study has used the superiority measure (Pi) of Lin and Binns and the ecovalence statistic (Wi) of Wricke in a biplot to identify the most tolerant genotypes. A novel statistic (WiPi) has been generated from this biplot which facilitates the simultaneous selection for general performance and yield stability of genotypes under a range of rust stress conditions.