Major gene resistance to Phakopsora pachyrhizi in Glycine canescens, a wild relative of soybean.

An analysis of the genetic basis of resistance to the soybean rust pathogen Phakopsora pachyrhizi in a set of differential lines of the wild plant Glycine canescens showed that resistance was dominant and controlled by genes with major phenotypic effects. Single resistance genes were detected in six of seven host lines. In the seventh line, two independently inherited genes for resistance were present. Intercrossing of most of these lines showed that some of these genes were inherited independently. In other cases, no F2 segregation was observed, implying that the resistance factors involved in the cross were closely linked or allelic. In yet other cases, distorted F2 segregation ratios were detected. It is suggested that these were generally caused by the wide nature of the crosses between morphologically and biochemically dissimilar accessions. At least four distinct resistance loci were detected in these lines of G. canescens. They have been given the tentative gene symbols Lr1, Lr2, Lr3 and Lr4.