Effects of air temperature on seed growth and maturation in cowpea (Vigna unguiculata)

This investigation has attempted to quantify the effects of air temperature on seedgrowth in cowpea independent of phenology and other major ontogenetic changes inthe physiology of the parent plant. Fruits produced in identical positions on the mainstem of plants (which, in three of the four environments tested, were almost identicalin dry weight and morphology at the onset of flowering) were harvested at regularintervals after anthesis. Four day-night temperature regimes (mean values inparentheses) were investigated: 33-24 C (283 C); 33-19 C (256 C); 27-24 C (254 C) and 27-19 C (228 C). Overall, the mean dry weight ofindividual seeds contained in the first fruit produced in the coolest regime was morethan double that recorded in the warmest environment, with the two intermediateregimes giving intermediate but similar results to each other. These final weightswere brought about by almost identical durations of the linear phase of increase indry weight (about 9 days) in the three warmer regimes but a longer duration (about 11 days) in the coolest regime, while the rates of increase in dry weight during thisphase were identical in the three cooler regimes (about 13 mg seed^-1 day^-1) butconsiderably less in the warmest environment (about 10 mg seed^-1 day^-1). Attributes of the first formed fruits are compared with ‘average’ fruits in eachenvironment and implications of these data in legume physiology and breeding are discussed.