Evaluation of Soybean Genotypes for Resistance to Three Seed-borne Diseases

Seed-borne diseases of soybeans caused by Phomopsis longicolla (Phomopsis seed decay), Cercospora kukuchii (purple seed stain), and M. phaseolina (charcoal rot) are economically important diseases that affect seed quality. Commercial cultivars marketed as resistant to all three diseases are not available. Reactions of 27 maturity group (MG) III, 30 early MG IV, 33 late MG IV, and 53 MG V genotypes were evaluated for resistance to these pathogens during the 2006 to 2008 growing season in the same field that had been in no-till production, not irrigated, and naturally and artificially infested. There was great variation in seed infection among genotypes and years, indicating the value of screening genotypes over multiple years. Some genotypes were resistant to these pathogens in one, two, or in all three years. Genotypes, DP 3478 (early MG IV), and RO1-769F (MG V) were resistant and DG4460 was moderately resistant to P. longicolla infection across three years. Genotypes AG3705 and FFR3990 (MG III) and DC20300, DC7816, Stoddard, and Ozark (MG V), were resistant to C. kukuchii infection during all three years. Ten genotypes in MG III, eight in early MG IV, seven in late MG IV, and 14 in MG V had no seed infection by M. phaseolina in all three years. These results indicate that seed infection comparison to these pathogens among genotypes should be made over several years, or false conclusions about resistance to any of the three pathogens may be made when disease is assessed for limited period of time. The genotypes identified as having resistance to each or combinations of the seed-borne diseases across the three years could be useful as a source for resistance in improving soybean seed quality. Accepted for publication 20 December 2012. Published 21 March 2012.