Breeding for resistance to bean common mosaic virus, halo bllght, pseudomonas phaseolicola and anthracnose, colletotrichum lidemutttlenum in common bean (phaseolus vulgaris L.)

Abstract

Five popular bean cultivars susceptible to bean common mosaic virus, halo blight Pseudomonas phaseolicola and anthracnose Colletotrichum lindemuthianum were crossed in a dial lei with two other cultivars resistant to these pathogens. Progenies were evaluated at the National Horticultural Research Centre - Thika and the University of Nairobi - Kabete. Lines combining resistance to two or more of the diseases were selected. Mode of inheritance of resistance to BCMV in cultivar L226-10 (52) and that of resistance to Pseudomonas phaseolicola and Col/etotrichum lindemunthianum in NB-123 were studied. Out of 1800 pollinations of the diallel crossing to seven bean cultivars, 1400 were successful, giving an overall 78.3% of successful crosses with each pod containing 3-7 seeds. L226-10 (52) was rated resistant to BCMV isolate 510 both in the green house and in the field. The F1' F2 and F3 progenies of the crosses GLP-2 x GLP-24, GLP-2 x M535, GLP-288 x GLP-24, GLP-24 x GLP-2, GLP-24 x M535, GLP-x.92 x M535, M535 x GLP-2, M535 x GLP-2, M535 x GLP-288, M535 x GLP-24 and M535 x GLP-x.92 were highly tolerant to the virus isolate both in the green house and in the field. NB-123 was rated resistant to Pseudomonas phaseolicola both in the green house and in the field. The F1' F2 and F3progenies with NB-123 and M535 as one of the parents were resistant to the pathogen both in the green house and in the field. NB-123 was rated resistant to Coletotrichum lindemuthianum both in the green house

and in the field. The Fl' F2 and F3 progenies with M535 and NB-123 as one of the parents had a high degree of resistance to the pathogen both in the green house and in the field. Segregation of the F2 progenies for resistance to BCMV of the crosses GLP-2 x L226-10 (52), GLP-x.92 x L226-10 (52) and their reciprocals did not differ from the expected ratio 3:1 (resistantsusceptible). Segregation of the F3 progenies for resistance to BCMV of the same crosses and their reciprocals also did not differ from the expected ratio 2:1 (segregating:non-segregating). It was therefore concluded that resistance to BCMV in L226-10 (52) is governed by a single dominant gene. TAe segregation of the F2 progenies for resistance to Pseudomonas phaseolicoJa of the crosses GLP-2 x NB-123, GLP- x.92 x NB-123 and their reciprocals differed from the expected ratio 3:1 (resistantsusceptible). Segregation of the F3 progenies for resistant to Pseudomonas phaseoJicoJa of the same crosses and their reciprocals differed from the expected ratio 2:1 (segregating:non-segregating).lt was therefore concluded that resistance to Pseudomonas phaseolicoJa in NB-123 is not governed by a single dominant gene. The segregation of the F2 proqenies for resistance to CoJ/etotrichum Jindemuthianum of the crosses GLP-2 x NB-123, GLP-x.92 x NB-123 and their reciprocals did not differ from the expected ratio 3:1 (resistant:susceptible). Segregation of the F3 progenies for resistance to CoJ/etotrichum Jindemuthianum for the same