GROWTH, YIELD AND PLANT-WATER RELATIONS OF 4 COWPEA (VIGNA-UNGUICULATA) CULTIVARS IN THE SAHEL

The response of four cowpea (Vigna unguiculata (L.) Walp.) cultivars t o the warm, semi-arid tropical environment at the ICRISAT Sahelian Cen ter at Sadore, Niger was studied during 1985 and 1986 in terms of leaf area index (LAI), dry matter (DM) accumulation, net photosynthesis, s tomatal conductance, total water use and yield. Among the three improv ed cultivars, IT82D-716 is early and erect, cv. IT83S-947 is early and spreading and cv. TVX4659-03E is a medium-duration, high-yielding, du al-purpose type. The local cv. Sadore Local is a long-duration, photos ensitive, spreading type used mainly for fodder. In both years, Sadore Local recorded the highest LAI. IT82D-716 and IT83S-947 produced < 1. 3 t/ha of DM in both years, whereas TVX 4659-03E produced > 2 t/ha of DM and proved superior to Sadore Local in partitioning DM into pods. T he four cultivars did not differ significantly either in stomatal cond uctance or in net phytosynthetic rates. Observed maximum photosyntheti c rates of c. 20 mu mol/m(2)/s lie at the bottom of the range 21-38 mu mol/m(2)/s reported for 31 cowpea genotypes in an earlier study. Phot osynthetic rates increased with increasing photon flux density. TVX465 9-03E had an advantage in total seed plus fodder yields while the loca l cultivar gave significantly greater fodder yields in both years. See d and fodder yields, as well as water-use efficiency, confirmed the ad vantages offered by the dual-purpose cultivar TVX4659-03E. Future bree ding efforts in the Sahel should focus on dual-purpose (grain/fodder) cowpea types.