Validation of RAPD markers for white mold resistance in two snap bean populations based on field and greenhouse evaluations

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White mold [Sclerotinia sclerotiorum (Lib.) de Bary] is a fungal disease that can reduce yield of beans (Phaseolus vulgaris L.). A recombinant inbred line population and an independent inbred backcross population were developed that share a common white mold resistant donor parent, G122. Both populations were evaluated for physiological resistance in the greenhouse using the oxalic acid test and a modified straw test (ST). The populations were also field evaluated for disease incidence (DI) and disease severity (DS). The heritabilities for physiological resistance based on greenhouse tests were higher than those based on field evaluations in both populations. Low rank correlations, ranging from r = 0.17 to r = 0.44, were observed between greenhouse and field-based evaluations over years and populations. Of 10 quantitative trait loci previously identified in independent dry bean populations for field resistance based on either DI or DS and the ST, only three markers, OJ09.950, Phs, and OC07.850, were associated with both the field (DI or DS) and the ST in the G122 x Astrel population. The results suggest that direct selection in the greenhouse based on the modified ST for physiological resistance, though higher in heritability, will result in a negligible correlated response for improved field performance for white mold resistance in snap bean populations where architectural traits and avoidance mechanisms may be more important than physiological resistance.

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