LEAF AREA DEVELOPMENT OF INTERSPECIFIC HYBRIDS OF Phaseolus vulgaris X Phaseolus acutifoiius UNDER VARYING IRRIGATION REGIMES

Eight lines of interspecific crosses between Phaseolus vulgaris (line DOR 362) and Phaseolus acutifoiius (89F50-18), were produced by Ihc Bean Breeding Program at the Department of Agronomy. The iirterspocific hybrids were produced by in vitro embryo rescue technique and one generation of backcrossing towards the P. vulgaris parent line. These hybrid lines were grown under four applications of irrigation and total rainfall consisting of 232, 212, 193, and 172 mm for the entire growing season. Under the high irrigation regime (232 mm) the leaf area index (LAT) of each hybrid was the same at 20 and 35 days aller planting (DAP). At 61 DAP only three hybrids differed from the parent P. vulgaris which had obtained the lowest LAI value (2.46). In the 212 mm irrigation treatment all hybrids obtained similar LAT both at 21 and 40 DAP. At 68 DAP. LAI values ranged from 2.51 lo 4,01. In the 193 mm irrigation treatment LAI values were similar both at 21 and 39 DAP, At 75 DAP two hybrids obtained higher LAI values than P. vulgaris which had obtained Ihe lowest LAI value (2.13). In the lowest irrigation treatment (172 mm) LAI values were drastically reduced. However four materials obtained LAI values that ranged from 2.42 lo 2.60, comparable to some hybrids grown in the higher irrigation treatments. Breeding lines had a significant effect on final yield, while the irrigation regimes had a highly significant effcct, In general all lines produced 36% more yield in the 212 mm irrigation treatment than the highest irrigation treatment (232 mm). Yield was reduced by 89 and 85% in the 193 mm and 172 mm irrigation treatments respectively, when compared to the 212 mm irrigation treatment. Leaf area index (LAI) was not an effective indicator for predicting yield performance of interspecific hybrids under low irrigation treatments. When a comparison was made between the 212 nun and 172 mm irrigation treatments, one hybrid's yield was reduced by only 38% while the rest were reduced by more than 76%, The use of interspecific hybrids did not prove capable of producing new lines adapted to lower water requirements,