Characterizing soybean rust resistance within populations of Glycine tomentella and the inheritance and characterization of soybean aphid resistance in PI 587663, PI 587677, PI 587685, and PI 594592

Soybean rust, caused by Phakopsora pachyrhizi Syd., is known to cause significant damage to soybean yields in many production areas worldwide. Most soybean cultivars are susceptible to the fungus and even though sources of resistance have been discovered within the USDA soybean germplasm bank, isolates of soybean rust can overcome that resistance, so other sources of rust resistance are needed to combat rust. The wild perennial Glycine species may contain unique rust resistance genes and many of the accessions evaluated to date were reported to have resistance to many diseases including rust. Although the wild perennial Glycine species may represent promising sources of rust resistance, producing hybrids between soybean and the perennial accessions has been problematic. Among the wild perennials, Glycine tomentella germplasm has been reported to contain rust resistance and has been the only perennial to successfully hybridize with soybeans to produce fertile offspring. In this study, four G. tomentella rust resistant germplasm accessions (PI 441008, PI 483218, PI 509501, and PI 583970) were crossed, two being reciprocal crosses (PI 441008 and PI 583970), with one rust susceptible accession (PI 441011) to generate four F2 populations that were evaluated for rust resistance. A F2:3 population was generated from the PI 441011 x PI 441008 for further evaluation. F2 and F2:3 individuals and parents were inoculated with P. pachyrhizi under controlled greenhouse conditions. Resistance was evaluated using a qualitative scale based upon lesion color and sporulation of uredinia. Segregation analysis of F2 and F2:3 populations suggested that the inheritance of resistance fit models of a single dominant or two dominant genes. The rust resistance genes may be distinctive and uniquely different from those found in soybean. Soybean aphids (Aphis glycines Matsumura) are a significant soybean [Glycine max (L.) Merr.] pest and pose a constant threat to the production of soybeans in the Midwest. Native throughout eastern Asia, soybean aphids first spread to Australia and then into North America where it has been found in 21 U.S. states and three Canadian provinces. Screening of the USDA germplasm collection has yielded several sources of aphid resistance. However, the identification of soybean aphid biotype 3 that colonizes plants with the Rag1 and Rag2 resistance genes has made the interaction between the aphid biotypes and resistance genes in soybeans more complex. Thus the continual assessment for aphid resistance in the USDA germplasm remains vital. Preliminary testing of 3000 accessions resulted in identifying new germplasm accessions PI 587663, PI 587677, PI 587685, and PI 594592, which demonstrate strong resistance to soybean aphid biotypes 1 to 3. The objectives of this study were to determine the inheritance of resistance, characterize the expression of resistance, and compare resistance of the four accessions with other sources against the three biotypes. F2 populations developed from crosses between the accessions and three susceptible genotypes (LD02-5320, LD03-6566, and LD03-10504) were tested for resistance. F2 plants from the crosses, when tested for resistance to biotype 3, fit a 3:1 ratio (single dominant genetic model). Segregation among F2:3 families from the crosses supported the single dominant resistance gene hypothesis. The four accessions, when compared to other known sources of aphid resistance, showed a strong resistance to biotypes 1 and 2 while also displaying a resistance to biotype 3