Heat tolerance in cowpea: effect of timing and duration of heat stress

Summary. Reproductive processes and pod yield in cowpea (Vigna unguiculata (L.) Walp), an important crop grown in semi‐arid sub‐Saharan Africa, are adversely affected by high temperature. Genotypic differences in heat tolerance have been identified under hot, long‐days, but it was not known if this tolerance is also exhibited in hot, short‐day environments typical of sub‐Saharan Africa. The objectives of the work reported here were to determine whether heat tolerance identified under hot, long‐days was expressed at the same stages of development under hot, short‐days, and whether responsiveness to temperature was additive and quantitative. A heat‐tolerant (Prima) and heat‐susceptible (IT84S‐2246) cultivar of cowpea were grown in controlled environments under short‐days (12 h day ‐1 ), initially at 30°C/24°C (Mod‐T), and then transferred at 0, 10, 20, 30 and 40 days after emergence (DAE) to 36°C/27°C (High‐T), where they remained for 5, 10 or 20 days duration before returning to Mod‐T. Control plants remained at Mod‐T or High‐T for 50 days, when the first pods were mature and the experiment was terminated. There were significant effects of duration (D) and timing (T) (P < 0.001), and interactions between D × T (P < 0.001), T × genotype (G) (P < 0.01) and D × T × G (P < 0.05) on pod weight plant ‐1 . Prima was significantly (P < 0.001) more tolerant to high temperature during flowering than IT84S‐2246, confirming that heat tolerance was expressed under hot, short days. The greater heat tolerance of Prima was associated with an ability to maintain peduncle and flower production at High‐T, and with greater podset. The sensitive period in IT84S‐2246 started at floral bud initiation (15–20 DAE), and effects of High‐T thereafter were additive and quantitative.