Genotypic classification of cowpea based on responses to heat and photoperiod

Heat and photoperiod influence reproductive development and yield of crop plants. In cowpea (Vigna unguiculata [L.] Walp.), genetic variation is present for heat tolerance and responses to photoperiod during different stages of reproductive development. A genotypic classification system had been developed based on responses to high temperature under long days. Further studies were needed under short and long days and hot and moderate temperatures to characterize genotypic variation for juvenility and photoperiod response and interactions with temperature. Forty-four contrasting cowpea genotypes were sown in the held with moderate (31.5/16.5 degrees C day/night) and hot (38/22.5 degrees C day/night) temperature long day environments and in glasshouses in hot (35/26 degrees C day/night) or moderate (32/18 degrees C day/night) temperatures under short (11 h 20 min at planting to 12 h 20 min after 30 d) and long (14 h 50 min at planting to 14 h 16 min after 30 d) days, and these genotypes were evaluated for juvenility and photoperiod and temperature responses. The genotypes were classified into 11 groups based on photoperiod response (change in position of the first reproductive node or period to appearance of floral buds in long compared with short days), juvenility (minimum period for appearance of floral buds when grown under short days), and suppression of floral bud development and pod set under hot long days. This classification system will aid breeders and agronomists In their understanding of the genetic variation for these characteristics and in choosing genotypes with appropriate juvenility, photoperiod response, and heat tolerance for breeding and agronomy programs serving tropical and subtropical production environments.