SELECTIVE MAPPING OF QTL CONDITIONING DISEASE RESISTANCE IN COMMON BEAN

Genetic markers linked with quantitative trait loci (QTL) may enable i ndirect selection of complex disease resistance. Construction of separ ate linkage maps to identify QTL for each complex disease resistance t rait of common bean (Phaseolus vulgaris L.) is unfeasible, however. We investigated whether selective mapping could be used to hasten identi fication of random amplified polymorphic DNA (RAPD) associated with QT L conditioning bean golden mosaic virus (BGMV) or common bacterial bli ght (CBB) resistance. The mapping population ('Dorado' x XAN 176) cons isted of 79 F-5:7 recombinant inbred lines. A bulked segregant analysi s (BSA) of as few as three individuals and selective genotyping was us ed. The 101 RAPDs identified between the parents were tested across re sistant vs. susceptible bulks for BGMV reaction, combined greenhouse ( lean and field reactions to CBB, and pod (greenhouse) reaction to CBB. Fourteen of 22 RAPDs selectively mapped because they cosegregated amo ng lines within bulks, were linked with seven of the nine QTL conditio ning resistance as identified by QTL mapping using all 101 RAPDs. The two QTL not identified by this approach had minor effects. BSA and sel ective genotyping required only about one-third the cost and labor of completely classifying the whole population with each marker and was s imilarly effective for identifying RAPD markers associated with major- effect QTL that condition disease resistance in common bean. Two-locus models (R(2)), for select environments, explained 60% of the phenotyp ic variation in BGMV reaction, and 65, 58, and 46% of the phenotypic v ariation in greenhouse-leaf, -pod, and field reactions to CBB. Repulsi on linkages between QTL for BGMV and CBB may complicate the combinatio n of resistance alleles for these two traits.