QTL Conferring Resistance and Avoidance to White Mold in Common Bean

Abstract

White mold, caused by Sclerotinia sclerotiorum (Lib.) De Bary, is a serious fungal disease that negatively affects production of common bean (Phaseolus vulgaris L.). Resistance to white mold in common bean is complexly inherited and comprised of physiological resistance and avoidance mechanisms. The objectives of this research were to discover quantitative trait loci (QTL) conferring resistance to white mold in navy beans, to determine if a multitrait bulking strategy was an efficient approach for locating QTL conferring resistance to white mold, and to identify agronomic traits associated with QTL for white mold avoidance in the field. A 98 F 3 -derived Bunsi/Newport population was evaluated in three environments for resistance to white mold and agronomic traits. A 28 recombinant inbred line population derived from a Huron/Newport cross was evaluated for the resistance and yield in four environments and was used to confirm marker associations. Marker BC20.1800 on B2 was associated with disease severity index (DSI) (12%) across environments, and was confirmed in the second population. Markers linked to QTL were also detected on B7 for DSI (17%), resistance to oxalate (16%), yield (37%), as well as days to flowering (14%), branching pattern (9%), lodging (9%) and seed size (20%). Growth habit unexpectedly mapped to B7, and represents a novel source of determinacy in navy bean. Multiple-trait bulking based on low DSI, high yield, and 40 to 45 d to flowering versus high DSI, low yield, and 40 to 45 d to flowering effectively identified more markers linked to QTL for resistance to white mold than did bulks based on low and high DSI alone. Selection based on QTL that confer resistance to white mold, such as the Bunsi-derived QTL located on B2 and B7 of the bean genome, combined with certain desirable agronomic traits offers the opportunity to develop resistant cultivars and improve our understanding of resistance to white mold in common bean.