Flowering in pigeonpea (Cajanus cajan) in Kenya: Responses of medium- and late-maturing genotypes to location and date of sowing

The effects of temperature and photoperiod on times From sowing to flowering (f) were investigated in medium- and late-maturing pigeonpea (Cajanus cajan). Twelve genotypes were sown in two seasons at seven sites in Kenya, covering latitudes 0-4 degrees S and a wide range of altitudes (50-2000 m), as well as under polythene enclosures constructed at six sites to create warmer temperature regimes (a total of 26 environments). The same genotypes were also sown at monthly intervals and in an artificially extended photoperiod (in the open as well as under polythene) created by incandescent lamps suspended above the plots at Katumani (1 degrees 30'S). Times from sowing to flowering varied from 70 to more than 300 days and were associated with variations in mean pre-flowering values of temperature and photoperiod which ranged from 15.2 degrees to 32.7 degrees C and from 12.6 to 15.0 h d(-1). Genotypic variation in f in the most inductive regimes (a mean pre-flowering temperature of 24.3 degrees C for the medium- and 20.8 degrees C for the late-maturing genotypes, combined with a mean pre-flowering photoperiod of 12.6 and 12.8 h d(-1)) ranged from 70 and 76 days and from 85 to 112 days, respectively. There were no photoperiodic effects on f over the range from 12.6 to 13.1 h d(-1), but the artificially extended day delayed flowering, especially in the late-maturing genotypes. The relation between 1/f and the mean pre-flowering temperature was linear below and above an optimum temperature, T-o. The genotype-specific parameters derived from these thermal linear rate models based on flowering responses in 26 environments closely predicted 1/f and therefore f in in an independent sequence of monthly sowings. It was thus responses to temperature below and above T-o, and not responses to daylength which modulated flowering throughout the wide range of natural environments tested within this vast country, even in the late-maturing and most photoperiod-sensitive genotypes.