TOWARDS THE RELIABLE PREDICTION OF TIME TO FLOWERING IN 6 ANNUAL CROPS .3. COWPEA VIGNA-UNGUICULATA

Six genotypes of cowpea (Vigna unguiculata) of diverse origin were sow n on various dates at five locations in Australia in order to provide a range of photothermal environments. Times from sowing to first flowe ring (f) ranged between 36 d and 145 d; pre-flowering temperature and photoperiod means varied from 15.7-degrees to 29.2-degrees-C and from 11.6 to 15.5 h d-1. In five genotypes there was no effect of photoperi od on rate of progress towards flowering (1/f), but the relation betwe en 1/f and mean temperature was always positive. The base temperatures (at which 1/f = 0) varied between 8.1-degrees and 10.4-degrees-C. The rankings of parameter estimates among four photoperiod-insensitive ge notypes common to this study and earlier research in controlled enviro nments were almost identical, and there was generally good agreement b etween field observations and predictions from controlled environments once hourly' temperatures were used to describe the natural environme nt. When cowpea plants were exposed to temperatures below 3-degrees-C, flowering was delayed beyond expected values, presumably as a result of chilling damage. In one genotype, rate of progress towards flowerin g was affected by both temperature and photoperiod, and relations betw een 1/f and the photothermal environment were described by a two-plane linear model of similar form to that determined in an earlier control led environment study. These latest findings support the utility of su ch linear models for the prediction of crop phenology in the field and for the genetic characterization of photothermal flowering response i n annual crops.