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CROP BREEDING & GENETICS

Marker-Assisted Backcrossing QTL for Partial Resistance to Sclerotinia White Mold in Dry Bean

USDA-ARS, Forage and Vegetable Crop Research Unit, 24106 North Bunn Rd., Prosser, WA, 99350. This research was supported by the National ARS Sclerotinia Initiative

^* Corresponding author (pmiklas{at}pars.ars.usda.gov).

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 BC₃F_4:6 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 BC₂F_4:6 inbred line populations. The B7 QTL in the BC₃F_4:6 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.

Abbreviations: DAP, days after planting • QTL, quantitative trait loci • Pop-I, Population I • Pop-II, Population II • Pop-III, Population III • Pop-IV, Population IV • RAPD, random amplified polymorphic DNA • SCAR sequence-characterized amplified region.