INHERITANCE OF RESISTANCE TO THE BEAN-POD WEEVIL (APION GODMANI WAGNER) IN COMMON BEANS FROM MEXICO

The bean-pod weevil (BFW), Apion godmani Wagner, often causes heavy lo sses in crops of common bean (Phaseolus vulgaris L.). Farmers need res istant bean cultivars to minimize losses, cut production costs, stabil ize seed yield, and reduce pesticide use and consequent health hazards . To design effective breeding methods, breeders need new and better s ources of resistance and increased knowledge of their modes of inherit ance. We therefore: (1) compared sources of resistance to BPW, (2) stu died the inheritance of resistance, and (3) determined whether the sou rces possess similar or different genes for BPW resistance. The follow ing sources of resistance, originating from the Mexican highlands, wer e evaluated for 3 years at INIFAP-Santa Lucia de Prias, Texcoco, Mexic o: 'Amarillo 153', 'Amarillo 169', 'Hidalgo 58','J 117','Pinto Texcoco ', 'Pinto 168', and 'Puebla 36'. All except 'Puebla 36' were crossed w ith the susceptible cultivar 'Jamapa'. 'Amarillo 153' and 'Puebla 36' were crossed with another susceptible cultivar, 'Bayo Mex'. The parent s, F-1 hybrids, and F-2 populations were evaluated for BPW damage in 1 992. Backcrosses of the F-1 of Jamapa/Pinto 168 to the respective susc eptible and resistant parents were also evaluated in 1992. All seven r esistant accessions were crossed in all possible combinations, excludi ng reciprocals. The resulting 21 F-1 hybrids and 21 F-2 populations we re evaluated for BPW damage in 1994. 'J 117' had the highest level of resistance to BPW. 'Pinto Texcoco' and 'Puebla 36' had the highest mea n damage score of all seven sources of resistance. The F-1 hybrids bet ween susceptible parents and resistant sources were generally intermed iate. Two genes segregating independently controlled the BPW resistanc e in each accession. One gene, Agm, has no effect when present alone, whereas the other gene, Agr, alone conferred intermediate resistance. When both genes were present, resistance to BPW was higher. Based on m ean BPW damage scores, all 21 F-1 hybrids and their F-2 populations, d erived from crosses among seven resistant accessions, were resistant. However, data from individual plant damage scores in F-2 populations o f Amarillo 169/Pinto 168 and Pinto Texcoco/Pinto 168 suggested that at least one gene in each of the three accessions was non-allelic. Data also indicated that 'Amarillo 169' had a dominant gene that conferred high levels of BPW resistance, irrespective of the alleles at the othe r locus; and that 'Pinto Texcoco' and 'Pinto 168' possessed two differ ent genes for intermediate resistance.