Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2001
Publication Date: 12/20/2001
Citation: BRADLEY, C.A., HARTMAN, G.L., NELSON, R.L., MUELLER, D.S., PEDERSEN, W.L. RESPONSE OF ANCESTRAL SOYBEAN LINES AND COMMERCIAL CULTIVARS TO RHIZOCTONIA ROOT AND HYPOCOTYL ROT. PLANT DISEASE. 2001. v. 85. p. 1091-1095. Interpretive Summary: Rhizoctonia root and hypocotyl rot of soybean is a common and widespread soil-borne fungal disease that causes damping-off as well as lesions on the hypocotyl and root. There are no commercial cultivars that are marketed as having resistance and few reports have been published on evaluation of soybean for resistance. The objective of this study was to evaluate the ancestral soybean lines from which current North American cultivars were developed, as well as privately and publicly developed commercial soybean cultivars, for resistance, and to identify sources of resistance that could be used immediately by growers and breeders to manage the disease. Most of the ancestral lines and cultivars evaluated were susceptible; however, 21 of the ancestral lines and 20 of the commercial cultivars were partially resistant. This information is the first extensive report that provides data on soybean resistance to the fungal pathogen that causes Rhizoctonia root and hypocotyl rot. This is of interest and use to both private and public soybean breeders that may want to use this resistance to develop high-yielding disease resistant cultivars.
Technical Abstract: Rhizoctonia root and hypocotyl rot is a common disease of soybean caused by Rhizoctonia solani. There are no commercial cultivars marketed as resistant to Rhizoctonia root and hypocotyl rot, and only a few sources of partial resistance to this disease have been reported. Ninety ancestral soybean lines, maturity groups (MGs) 000 to X, and 700 commercial cultivars, MGs II to IV, were evaluated for resistance to R. solani under greenhouse conditions. Most of the ancestral lines and cultivars evaluated were susceptible; however, 21 of the ancestral lines and 20 of the commercial cultivars were partially resistant. Of the 21 ancestral lines, CNS, Mandarin (Ottawa), and Jackson are in the pedigree of cultivars previously reported as being partially resistant to R. solani. In an additional study, dry root weights of 21 soybean cultivars were evaluated after inoculation with R. solani. Variation in dry root weight occurred among cultivars, but there was not a significant (P = 0.05) correlation between dry root weight and disease severity.