Physiological and biochemical responses of cowpea genotypes to water stress under glasshouse and field conditions

Five cowpea genotypes, Gorom local (Go), KVX61-1 (KV), Mouride (Mo), Barnbey 21 (1321) and TN88-63 (TN), differing in their susceptibility to water stress, were studied under glasshouse and field conditions, to determine their physiological, biochemical and agronomic responses to water deficit at flowering stage. Effect of water deficit on leaf water potential (psi(1)), canopy temperature, gaseous exchange, leaf proline content, total protein and starch contents, maximal quantum yield (phi p(0)) and yield components was examined. Water deficit significantly increased the canopy temperature and the proline content of the five genotypes while psi(1), gaseous exchanges, phi p(0) and starch content decreased significantly. Yield components, with the exception of seed number per pod, of the five genotypes, were also significantly affected. Under glasshouse and field conditions, the results showed that stomatal closure is the common strategy used by the five genotypes to avoid dehydration. Go, Mo and TN tolerated water stress better than B21 and KV. Furthermore, Go and Mo recovered more rapidly after rewatering than B21 and KV. These latter genotypes are revealed to be sensitive with low recovery capacity. The results suggest that the maintenance of net photosynthesis and solute accumulation seem to be traits conferring water stress tolerance in Go, Mo and TN. These traits and recovery capacity could be valuable selection criteria for higher yields under water deficit conditions.