Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/31/2001
Publication Date: 12/20/2001
Citation: HOFFMAN, D.D., DIERS, B.W., HARTMAN, G.L., NICKELL, C.D., NELSON, R.L., PEDERSEN, W.L., COBER, E.R., GRAEF, G.L., STEADMAN, J.R., GRAU, C.R. SELECTED SOYBEAN PLANT INTRODUCTIONS WITH PARTIAL RESISTANCE TO SCLEROTINIA SCLEROTIORUM. PLANT DISEASE. 2001. v. 86. p. 971-980. Interpretive Summary: Sclerotinia stem rot (SSR), caused by Sclerotinia sclerotiorum, is a major soybean (Glycine max) disease in the north central region of the United States (U.S.) and throughout the world. Current sources of genetic resistance to this disease only provide partial protection and few sources of resistance are known. The purpose of the research was to evaluate introduced soybean lines in maturity groups I to IV from the USDA Soybean Germplasm Collection for resistance to SSR, to evaluate the agronomic characteristics of the most resistant lines and to compare results from tests for resistance in the field and in the greenhouse. From 1995 to 2000, a total of 6,415 soybean lines were evaluated. After 3 years of testing all but 68 lines had been eliminated because of susceptibility to SSR. Additional disease testing and agronomic evaluation in 1999 and 2000 identified seven lines with the highest level of resistance to SSR and with height, maturity and lodging values similar to the resistant varieties included in the tests. Greenhouse screening techniques were identified that produced similar results with field tests. This is the first large scale screening of soybean germplasm for resistance to SSR and identifying new sources of resistance to this disease with be useful to soybean breeders. The evaluation procedures developed in this research will be beneficial to all scientists working with this disease.
Technical Abstract: Sclerotinia stem rot (SSR) is a major soybean disease. The few known sources of SSR resistance do not provide complete resistance. The objectives of this study were to 1) to identify new sources of resistance to SSR, 2) evaluate agronomic characteristics of the most resistant lines, and 3) correlate field disease severity of the most resistant PIs with agronomic characteristics and results from greenhouse and laboratory tests. 6,415 maturity group (MG) 0-IV PIs were evaluated for resistance in small plots for 3 years. Lines with the most disease resistance were evaluated in large plots for 3 years. Agronomic traits were recorded in tests in Urbana, IL for 3 years. The selected PIs were evaluated with an excised leaf inoculation (ELI) and petiole inoculation technique (PIT). Three years of evaluations identified 68 lines as most resistant. In field tests the selected MG I-III PIs with greater disease severity were significantly associated with taller plant heights and greater canopy closure. All other agronomic traits evaluated were not associated or were inconsistently associated with disease severity. The overhead misting system used in Urbana reduced the effect of escape mechanisms such as short plant height and reduced canopy closure. PIs 153282, 189931, 196157, 398637, 417201, 423818, and 561331 had high levels of resistance and were agronomically similar to the resistant standards. The PIT technique had a high and significant correlation with disease severity in the MG I and II field tests and could serve as a useful tool for evaluating soybean germplasm for SSR resistance in the greenhouse. The partially resistant Pis identified in this study could be valuable for incorporating SSR resistance into elite germplasm.