Physiological, biochemical and agromorphological responses of five cowpea genotypes (Vigna unguiculata (L.) Walp.) to water deficit under glasshouse conditions

Five genotypes of cowpea (Vigna unguiculata), Bambey 21, Gorom local, KVX61-1, Mouride and TN88-63, grown in pots under glasshouse conditions, were submitted to water deficit by withholding irrigation at vegetative stage (T1) for 14 days, and at flowering stage (T2) for 12 days. Effect of this stress on leaf water potential, gas exchanges, foliar proline, total protein and starch contents, maximal quantum yield of photochemistry (fp0), root volume and yield components was determined. Leaf water potential decreased significantly only for Mouride and TN88-63 (from -0.55 to -0.92 MPa on average) at T2 while root volume, gas exchanges and foliar starch content decreased for the five genotypes under water stress conditions at T1 and T2. fp0 was not affected during water deficit at T1. Significant decrease of fp0 was observed at T2 on the 6th day after stress induction (Dasi) for Gorom, KVX61-1 and TN88-63 and the 10th Dasi for Bambey 21 and Mouride. Proline was significantly accumulated during water stress at the 2 stages, Mouride and TN88-63 showed the highest contents in the case of T2 (2.88 and 3.3 mg.g-1 DM respectively). Water deficit did not affect significantly the total proteins contents for the 5 varieties at T1 and T2. Our results showed that the 5 varieties involved drought avoidance mechanism by decreasing stomatal conductance and transpiration at the 2 stages. Proline accumulation, maintenance of total protein content and starch decrease under stress conditions at T1 and T2 could probably contribute in turgor maintenance. In addition, these solutes contributed probably in the protection of photosynthetic apparatus (PSII) against denaturation notably during water stress at flowering stage. At the two stages water stress reduced significantly seed number per pod and seed number per plant but the genotypic variation observed revealed that Bambey 21 was less affected than Gorom, TN88-63 and Mouride whereas KVX61-1 was most affected. Bambey 21 proved to be tolerant to water stress at the two stages, Gorom, Mouride and TN88-63 were intermediate and KVX61-1 sensitive.