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Submitted to: Crop Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/10/2007 Publication Date: 5/1/2007 Citation: Miklas, P.N. 2007. Marker-assisted backcrossing QTL for partial resistance to Sclerotinia white mold in dry bean. Crop Science. 47:935-942. Interpretive Summary: This is the first report to validate application of marker-assisted selection for development of dry bean cultivars with resistance to white mold. This disease causes $25 million in losses each year due to reduced quality and yield. Genetic resistance is an important component of integrated control strategies to manage this disease, but is difficult to breed for because of low heritability. Marker-assisted selection can be used to improve breeding efficiency for traits with low heritability, but has not yet been demonstrated in breeding for genetic resistance to white mold in bean. In this study we describe the actual utility of marker-assisted selection for two different sources of resistance to white mold. Pinto and great northern beans with improved genetic resistance to white mold were developed. These results and germplasm will lead to improved control of the most devastating disease facing dry bean in the U.S. Technical Abstract: White mold caused by Sclerotinia sclerotiorum (Lib.) de Bary is a major disease limiting dry bean (Phaseolus vulgaris L.) production. Genetic resistance provides some control but is difficult to breed for because of low heritability. We sought to determine if marker-assisted selection for quantitative trait loci (QTL) conferring partial resistance could facilitate breeding for resistance to white mold in dry bean. The Phs marker linked with a QTL derived from landrace G122 on linkage group B7 was backcrossed into ‘Winchester’ pinto forming two BC3F4:6 inbred line populations. The AW9.1200 and SS18.1650 markers linked with a QTL from snap bean breeding line NY6020-4 on B8 were backcrossed into ‘Maverick’ pinto and ‘Matterhorn’ great northern forming BC2F4:6 inbred line populations. The B7 QTL in the BC3F4:6 populations on average explained 52% of the phenotypic variation for disease reaction in the greenhouse test and 10% across four field tests. The B8 QTL explained 30% in the greenhouse and 10% in the field. Averaged across tests and populations the B7 and B8 QTL conditioned 15% and 17% reduction in disease severity score, respectively. Linkage drag from selection of the B7 QTL was observed for yield. MAS for the B7 and B8 QTL was an effective breeding tool for introgressing partial resistance to white mold into susceptible pinto and great northern dry bean market classes, but further selection for agronomic performance may be required to obtain lines worthy of commercial production. |
