CHARACTERIZATION OF STEM CANKER RESISTANCE IN HUTCHESON SOYBEAN

Stem Canker caused by Diaporthe phaseolorum (Cooke & Ellis) Sacc. f. s p. meridionalis Morgan-Jones (Dpm) can cause significant yield losses in soybean [Glycine max (L.) Merr.] in the southern USA. Some cultivar s are known to be resistant to the disease; however, the parental dono r, level, and inheritance of stem canker resistance for most of those cultivars is unknown. The objective of this study was to characterize stem canker resistance in 'Hutcheson', a widely used parent in breedin g programs. To determine the inheritance of resistance and allelic rel ationships with known genes, Hutcheson was crossed with susceptible ge notypes 'Hartwig' and J77-339 and four lines carrying Rdc1, Rdc2, Rdc3 , or Rdc4. Crosses were made in the field at Stoneville, MS, in 1993. The parents of Hutcheson and the six F-2 populations were toothpick in oculated in the field in 1993 and 1994, respectively. In 1994, Hutches on and 29 other soybean genotypes were inoculated with four isolates o f Dpm and external lesion length was recorded as a measure of level of resistance. Genetic ratios from F-2 populations indicate that resista nce in Hutcheson is conferred by a single dominant gene that is alleli c with Rdc4. 'York' was determined to be the parental donor of resista nce carried by Hutcheson. Isolates differed in virulence. Hutcheson an d several other genotypes were highly resistant to all isolates. Hutch eson should continue to be an excellent source of stem canker resistan ce.