Flowering in Faba Bean: Genotypic Differences in Photoperiod Sensitivity, Similarities in Temperature Sensitivity, and Implications for Screening Germplasm

Reanalyses of extensive results from three separate controlled environment studies show that the rate of progress towards flowering in plants of the Sudanese faba bean (Vicia faba L.) land-race Zeidab Local responds consistently and without interaction to photoperiod and sub-optimal temperatures across all investigations, with no specific low-temperature vernalization response. Moreover, the additive model developed to describe the photothermal response is sufficiently robust to show that the range between the two boundary photoperiods is substantial, and so covers most agricultural environments: the critical photoperiod, below which flowering is delayed, is ≥ 18 h d−1; and the ceiling photoperiod, i.e. the longest photoperiod which gives the maximum delay in flowering, is ≈ 7·5 h d−1 Despite their different origins, Zeidab Local and the UK cv. Maris Bead show a similar sensitivity of rate of progress towards flowering to temperature and also to photoperiod. Differences in the base and optimum temperatures are, however, substantial. Data for other diverse genotypes of faba bean also provide no evidence of any significant variation in the sensitivity of rate of progress towards flowering to temperature, but sensitivity to photoperiod varies greatly. A simple method of characterizing the sensitivity of time to flower to fluctuating field environments in the faba bean germplasm is proposed.