Selection for bean golden mosaic resistance in intra- and interracial bean populations

Bean golden mosaic (BGM) resistance within any one bean (Phaseolus vulgaris L.) race is inadequate. Pyramiding genes from different races would increase resistance and reduce pesticide use. Our objectives were to: (i) pyramid and compare BGM resistance of genotypes from intraracial versus interracial populations, (ii) verify pyramided resistance by means of molecular markers, and (iii) combine BGM resistance with resistance to other diseases. One intraracial (GV 10625) and four interracial (DC 10622, GV 10624, GV 10626, and GV 10627) populations were developed at CIAT. Plants within each F1-derived F2 (F1:2) were advanced in bulk. The F3 was grown in the field under common bacterial blight [CBB, caused by Xanthomonas campestris pv. phaseoli (Smith) Dye] and angular leaf spot [ALS, caused by Phaeoisariopsis griseola (Sacc.) Ferraris] pressure. Single plant selections were made in the F3 and F4 Plants within F4:5 were harvested in bulk to screen for ALS, bean common mosaic (BCM), BGM, and CBB. The 39 selected genotypes, 12 parents, and six checks were again evaluated for the four diseases. Seventeen genotypes, parents, and checks also were screened for the RAPD marker OR2530 linked with bgm-1 gene and the SCAR marker SW12700 linked with a QTL controlling BGM resistance. Selected genotypes differed in their BGM reaction. None of the genotypes from the intraracial population were resistant to BGM. Five genotypes with the highest resistance were obtained from GV 10626 and GV 10627. DC 10622 and GV 10624 produced genotypes with intermediate resistance. Three genotypes from DC 10622 and four from GV 10627 possessed OR2530 marker linked with resistance derived from `Garrapato' and SW12700 marker linked with resistance derived from `Porrillo Sintetico'. All genotypes possessed the I gene for BCM and were intermediate to ALS. Five also were intermediate for CBB. Combined use of interracial populations, disease screening, and molecular markers should be emphasized for resistance breeding.