Relationships Among Three Genes Conferring Specific Resistance to Rust in Soybeans¹

Abstract

This study was conducted in containment facilities to further elucidate the genetic basis of specific resistance to Phakopsora pachyrhizi Syd. (incitant of soybean rust) among three soybean [ Glycine max (L.) Merr.] lines previously reported to each have a single dominant gene conferring resistance. F 4 lines, D79‐9690 and D79‐9697, each having rust resistance derived from PI 230970, were crossed with PI 462312 (‘Ankur’) and PI 200492, respectively. The cross PI 462312 ✕ PI 200492 also was made. F 2 populations and selected F 3 lines were evaluated for their reactions to two soybean rust isolates, Taiwan‐72‐1 and India‐73‐1. For each plant tested, a leaflet of a single trifoliolate leaf was inoculated with the Taiwan rust isolate and another leaflet was inoculated with the India isolate. PI 230970 and the two breeding lines D79‐9690 and D79‐9697 gave a resistant reaction to both isolates. PI 462312 gave a resistant reaction to the India isolate and PI 200492 an immune reaction to that isolate, but both were susceptible to the isolate from Taiwan. Our results confirmed previously published reports that each soybean line carried a single dominant gene for resistance and demonstrated that each gene was at a different locus. The genotypes for rust reaction assigned to the three parental types were: PI 200492, Rpp 1 Rpp 1 rpp 2 rpp 2 rpp 3 rpp 3 ; PI 230970, rpp 1 rpp 1 Rpp 2 Rpp 2 rpp 3 rpp 3 ; and PI 462312, rpp 1 rpp 1 rpp 2 rpp 2 Rpp 3 Rpp 3