Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 1, 2003
Publication Date: June 1, 2003
Citation: MIKLAS, P.N., DELORME, R.M. IDENTIFICATION OF QTL CONDITIONING RESISTANCE TO WHITE MOLD IN SNAP BEAN. JOURNAL OF AMERICAN SOCIETY OF HORTICULTURAL SCIENCES, 128:564-570. 2003. Interpretive Summary: Sclerotinia white mold has been considered a major disease of snap bean for many years. Fungicides used to control the disease combined with white mold induced yield loss cost U.S. snap bean growers about $15 million annually. Beans generally lack genetic resistance to this disease, but recent progress by ARS scientists suggests otherwise. A collaborative project (CRADA) between Dr. Miklas (ARS-Prosser, WA) and Dr. Riley of Syngenta Seeds (Nampa, ID) revealed existence of a major gene conditioning partial resistance to white mold. They located this gene on linkage group B8 of the bean map. A second gene with less effect was also discovered. This gene resided on linkage group B6. These genes were identified in a breeding line with partial resistance to white mold previously developed by Cornell University scientists. DNA markers tightly linked with these genes were obtained. The value of these genes and linked markers in a breeding program remains to be determined. However, a negative association between resistance and increased internode length in snap bean, suggests the genes may be more useful in dry bean breeding programs.
Technical Abstract: Quantitative trait loci (QTL) analysis of partial resistance to Sclerotinia white mold disease was studied in a segregating snap bean population (Benton/NY6020-4). Benton is a typical commercial snap bean cultivar susceptible to white mold. The non-adapted snap bean breeding line NY6020-4 is known to possess partial resistance. Selective mapping detected two QTL conditioning partial resistance to white mold on linkage groups B6 and B8 of the core map. The B6 and B8 QTL independently explained 12 and 38% of the phenotypic variation for disease reaction in the straw test and 14 and 26% in the field, respectively. The major-effect QTL on B8 for greenhouse and field resistance derived from NY6020-4. The B8 QTL was associated with longer 1st internode length, which is an undesirable trait in commercial snap bean cultivars. In conclusion, integration and utilization of partial resistance from NY6020-4 in a commercial snap bean background does not appear promising because of associations with increased lodging and increased internode length. The partial resistance from NY6020-4, conferred by B6 and B8 QTL, should be useful in a dry bean background, however, where disease avoidance is generally lacking and internode length does not influence commercial phenotype.