THE IMPROVEMENT OF LIMA BEAN (PHASEOLUS LUNATUS L.) WITH A VIEW TO INTENSIFY ITS CULTIVATION IN THE LOWLAND TROPICAL REGIONS. (FRENCH TEXT)

A complete review of origin, botany, ecology, genetic and improvement of Phaseolus lunatus emphasizes numerous gaps in the knowledge of the crop and a very limited utilization of its real genetic variability. Breeding works in the humid tropics have been neglected in the past. Evaluation trials of a germplasm collection at Ibadan (Nigeria) identified the principal problems of the crop intensification. Bush cultivars mainly selected in the low rainfall regions of the United States did not perform very well in the humid tropics owing to their diseases susceptibility and poor architecture. Among the climbing forms, high and stable yielding cultivars combining earliness and insensitivity to photoperiod were found in the cultigroup Sieva. Sources of resistance were also identified for three major enemies: two viral diseases, golden mosaic and green mottle and root knot nematodes of Meloidogyne sp.. The cultigroup Big Lima, not well adapted in the humid forest regions, contained the only sources of resistance to golden mosaic, the major constraint of the intensive cropping in this ecological zone. F2 and F3 individuals from crosses between Big Lima and Sieva cultivars combined resistance to this disease with earliness and good seed productivity. Wild forms of the variety silvester were very susceptible to golden mosaic but through crossing improve vigour, drought tolerance and level of fertility of the cultivated types. A good fertility restoration was obtained from interspecific hybrids with three wild species (P. metcalfei, P. polystachyus and P. unidentified). First generations of selfing and backcrossing did not reveal the presence of undesirable linkage blocks. The wild species showed a high level of resistance or immunity to golden mosaic and green mottle. Those characteristics were transmitted to some interspecific hybrids tested on the field at Ibadan.