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

Bean golden mosaic (BGM) resistance within any one bean (Phaseolus vulgaris L.) race is inadequate. Pyramiding genes from different races would increa se resistance and reduce pesticide use. Our objectives were to: (i) pyramid and compare BGM resistance of genotypes from intraracial versus interracia l populations, (ii) verify pyramided resistance by means of molecular marke rs, 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 F-1-de rived F-2 (F-1:2) were advanced in bulk. The F-3 was grown in the field und er common bacterial blight [CBB, caused by Xanthomonas campestris pv. phase oli (Smith) Dye] and angular leaf spot [ALS, caused by Phaeoisariopsis gris eola (Sacc) Ferraris] pressure. Single plant selections were made in the F- 3 and F-4. Plants within F-4:5 were harvested in bulk to screen fur ALS, be an common mosaic (BCM), BGM, and CBB. The 39 selected genotypes, 12 parents , and six checks were again evaluated for the four diseases. Seventeen geno types, parents, and checks also were screened for the RAPD marker OR2(530) linked with bgm-1 gene and the SCAR marker SW12(700) linked with a QTL cont rolling 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 front GV 10626 a nd GV 10627. DC 10622 and GV 10624 produced genotypes with intermediate res istance. Three genotypes from DC 10622 and four from GV 10627 possessed OR2 (530) marker linked with resistance derived from 'Garrapato' and SW12(700) marker linked with resistance derived from 'Porrillo Sintetico'. All genoty pes possessed the I gene for BCM and were intermediate to ALS. Five also we re intermediate for CBB. Combined use of interracial populations, disease s creening, and molecular markers should he emphasized for resistance breedin g.