Soybean rust resistance derived from Glycine tomentella in amphiploid hybrid lines

Soybean rust (SBR), caused by the fungal pathogen Phakopsora pachyrhizi Syd., has the potential to cause significant economic yield loss in U.S. soybean production. Four single dominant resistance genes have been identified in soybean [Glycine max (L.) Merr.] that only confer specific resistance to a few rust isolates that have been tested. Additional resistance genes have been identified in wild perennial relatives, including G. tomentella Hayata (accession PI 483218, 2n = 78). Intersubgeneric hybrids have been created between G. max (cv. Altona) and this G. tomentella accession. Amphiploid hybrid lines (2n = 118) were the result of this hybridization and when further backcrossed to G. max (cv. Clark 63), derived fertile lines (2n = 40) were also generated. Both sets of progeny were screened at the USDA-ARS facility at Ft. Betrick, MD, to determine if the resistance to SBR was inherited in the subsequent populations. The amphiploid hybrid clones still retained the genetic SBR resistance that was found in the G. tomentella parent. However, the derived fertile lines were susceptible. These lines were not screened for SBR resistance following each backcross, which may explain this occurrence. Reinstituting the backcross procedure, while testing for SBR resistance at every generation, could move the SBR resistance gene(s) from G. tomentella to the cultivated soybean G. max.