Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/7/2002
Publication Date: 11/1/2002
Citation: Hoffman, D.D., Diers, B.W., Hartman, G.L., Nickell, C.D., Nelson, R.L., Pederson, W.L., Cober, E.R., Grael, G.L., Steadman, J.R., Grau, C.R. 2002. Selected soybean plant introductions with partial resistance to selerotinia sclerotiorum. Plant Disease; 2002. Interpretive Summary: Sclerotinia stem rot, caused by a fungus, is a major soybean disease n north-central regions of the U.S., and southern Canada, where it can cause significant economic losses. Infection of soybean by S. Sclerotiorum is initiated by ascospores germinating and colonizing flower petals. The fungus grows into stems and girdles them, causing pods and seeds to abort. Soybean cultivars have been identified with partial resistance to S. Sclerotiorum in field evaluations, current sources of resistance in commercial cultivars are limited, and these sources do not completely prevent yield loss. The objectives of this study were to 1) evaluate soybean plant introductions to identify new sources of resistance to Sclerotinia stem rot, 2) evaluate the agronomic characteristics of the most resistant plant introductions, and 3) correlate field disease severity of the most resistant plant introductions with agronomic characteristics and results form greenhouse and laboratory resistance tests. A total of 6,520 maturity group (MG) 0-IV plant introductions (PI) were evaluated for disease resistance. All but 68 Pis were eliminated because of their susceptibility to Sclerotinia stem rot. The partially resistant Pis identified in this study can be valuable in incorporating Sclerotinia stem rot resistance into elite germplasm. These results are important to soybean growers, seed companies, and to other researchers interested in developing soybean breeding lines with resistance to this fungal pathogen.
Technical Abstract: Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is a major soybean (Glycine max) disease in north-central regions of the United States (U.S.) And throughout the world. Current sources of resistance to Sclerotinia stem rot express partial resistance, and are limited in number within soybean germplasm. A total of 6,520 maturity group (MG) 0-IV plant introductions (Pis) were evaluated for disease resistance in the U.S. and Canada in small plots or in the greenhouse from 1995 to 1997. Selected Pis with the most disease resistance were evaluated for resistance in the U.S. and Canada in replicated large plots from 1998 to 2000. Agronomic traits recorded on plots in the MG I-III tests in Urbana, IL from 1998 to 2000 were flowering date, percent canopy closure at three dates, maturity date, plant lodging at two dates, plant height, and seed yield. The selected PIs also were evaluated with an excised leaf inoculation and petiole inoculation technique. After the 1997 to 1997 evaluations, all but 68 Pis were eliminated because of their susceptibility to Sclerotinia stem rot. In field tests in Urbana, higher disease severity in selected MG I-III Pis was significantly (P greater than 0.05) associated with taller plant heights and greater canopy closure. All other agronomic traits evaluated were not associated or were inconsistently associated with disease severity Maturity group I-III Pis 153.282, 189.931, 196.157, 398.637, 417.201, 423.818, and 561.331 had high levels of resistance and were agronomically similar to the resistant standards. The resistance ratings from the petiole inoculation technique had a high and significant (P greater than 0.01) correlation with disease severity in the MGI and II field test. The partially resistant Pis identified in this study can be valuable in incorporating Sclerotinia stem rot resistance into elite germplasm.