Heat injury to reproductive development in cowpea (Vigna unguiculata (L.); Walp.) under ambient and elevated carbon dioxide concentrations

Physiological basis of heat injury during reproductive development was studied using contrasting cowpea (Vigna unguiculata (L.) Walp.) genotypes subjected to different night temperatures and light qualities under ambient and elevated levels of (CO;High night temperature during the vegetative and early reproductive stages causes complete suppression of floral buds on the main stem. Transfer experiments demonstrated that plants were not sensitive to heat at a particular stage of development but that the duration of heat experience is critical for floral bud development. Two weeks or more of continuous or interrupted heat caused complete suppression of all floral buds suggesting that the heat stress effect was cumulative over time. The degree to which high night temperature suppressed floral bud development depended on the R/FR ratio during the day and values of 1.3 to 1.6 were required to elicit the same responses as occur under natural sunlight.;High night temperature during anther development causes male-sterility and results in no pod set due to low pollen viability and anther indehiscence. The stage of floral development most sensitive to heat occurred nine to seven days before anthesis. During this period, premature degeneration of the tapetal tissue and lack of endothecial formation were detected in heat stressed plants. These two abnormalities may be responsible for the low pollen viability, low anther dehiscence and low pod set observed under heat stress.;Under high night temperature, different heat sensitive genotypes either produced no flowers or set no pods at either ambient or elevated (CO...