TOWARDS THE RELIABLE PREDICTION OF TIME TO FLOWERING IN 6 ANNUAL CROPS .4. CULTIVATED AND WILD MUNG BEAN

Eight genotypes of cultivated mung bean, black gram and rice bean (Vigna mungo, Vigna radiata ssp. radiata and Vigna umbellata, respectively) were sown at six sites in Australia on various dates in order to provide a range of photothermal environments. In addition, four accessions of the related wild species Vigna radiata ssp. sublobata were sown on five occasions. Times from sowing to first flowering (f) varied between environments from 34 to 317 d; pre-flowering temperature and photoperiod means ranged from 12.7-degrees to 29.1-degrees-C and from 11.8 to 15.5 h d-1. No effect of photoperiod was detected on rate of progress towards first flowering (1/f) in, four genotypes, but in each case a significant positive relation was detected between 1/f and mean temperature. These simple thermal time relations did not differ significantly among these four genotypes; the common base temperature was 7.9-degrees-C. In two genotypes observations were well described by a thermal response plane when the mean photoperiod was less than 13 h d-1 (p < 0.01) but photoperiods greater than 14 h d-1 delayed flowering. In each of the remaining genotypes the observations were best described by photothermal planes, that is, 1/f was modulated by temperature and photoperiod. Predictions from the models based on our data were in good agreement with the times to first flowering observed in three genotypes in an earlier controlled environment study.