Submitted to: Proceedings of the International Sclerotinia Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 3/1/2004
Publication Date: 3/10/2004
Citation: Miklas, P.N. 2004. Marker-assisted backcrossing of two white mold resistant qtl into susceptible pinto bean: ii. germplasm advancement and marker assessment. 2nd Sclerotinia Initiative Meeting, Minneapolis, MN. p. 3.
Technical Abstract: Resistance to white mold [Sclerotinia sclerotiorum (Lib.) de Bary] in dry bean (Phaseolus vulgaris L.) is quantitatively inherited with low to moderate heritability. Evaluation of resistance is further complicated by expression of both avoidance traits and physiological mechanisms. The identification of quantitative trait loci (QTL) with major-effect on resistance provides an opportunity to use marker-assisted breeding to combine resistance sources and expedite development of cultivars with enhanced levels of white mold resistance. Two such QTL, with expression in both the greenhouse straw test and field, derive from different sources: G122, a large-seeded landrace from India, and NY6020-4, a snap bean breeding line from Cornell University. The QTL from G122 and NY6020-4 reside on different linkage groups, B7 and B8, respectively. Tightly linked DNA markers (SCARs and RAPDs) were used to introgress the QTL into susceptible pinto bean cultivars 'Winchester' (B7 QTL) and 'Maverick' (B8 QTL) using up to three marker-assisted backcrosses. Four populations (Pop-1, Pop-2, Pop-3, Pop-4), consisting of 50, 38, 52, and 33 BC3F2 plants have been advanced to BC3F4:5 lines. The BC3F4 plants have been assayed for the QTL linked markers. For each population tested, a 1:1 expected segregation ratio for presence and absence of the markers among BC3F4 plants was observed. The next and final step will be to compare by regression the marker genotype with disease reaction phenotypes obtained for BC3F4:5 lines in replicated greenhouse and field tests to be conducted in 2004. Together, the regression and agronomic trait analyses will determine whether marker-assisted backcrossing for the B7 and B8 QTL will be useful for improving white mold resistance in susceptible pinto bean.