IMPROVING PHASEOLUS GENOTYPES FOR MULTIPLE CROPPING SYSTEMS

Common bean, Phaseolus vulgaris L. is intercropped or relay cropped wi th maize in many Andean highlands of Colombia and Peru. Breeding beans for the target multiple cropping systems is essential for the develop ment of productive and sustainable agriculture for the Andean smallhol ders. Outline of the breeding programme should follow the farming syst em approach with the establishment of on-farm trials and early farmers involvement. Bean breeding is oriented to minimize intercrop competit ion and to stabilize complementarity with maize. Genetic traits needed for improved varieties are divided as follows : traits not interactin g with the cropping systems, traits specific to intercrops and traits related with socioeconomic and seed quality aspects. Screening, prebre eding and recombination nursery are better made under sole cropping wh ile varietal improvement and on-farm trials are conducted under the ta rget multiple cropping systems. Breeding schemes may involve recurrent , pedigree and bulk hybrid selection. The given application concerns t he genetic improvement of P. coccineus, P. polyanthus and interspecifi c hybrids of P. vulgaris for both simultaneous and relay intercropping in Colombia and Peru. Earliness, cold tolerance, resistance to fungus diseases (mainly Ascochyta leaf blight and anthracnosis) and seed yie ld potential were the major objectives of the bean improvement program me. Priority has been given to the exploitation of the large diversity available in the secondary gene pool of common bean.