Effects of Temperature, Photoperiod and Seed Vernalization on Flowering in Faba Bean Vicia faba

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Abstract
Factorial combinations of three photoperiods (10, 13 and 16 h), two day temperatures (18 and 28 °C) and two night temperatures (5 and 13 °C) were imposed on nodulated plants of six diverse genotypes of faba bean (Vicia faba L.). Plants were grown in pots in growth cabinets from both vernalized (1.5±0.5 °C for 30 d) and non-vernalized seeds. The times from sowing to the appearance of first open flowers (f) were recorded. Seed vernalization decreased the subsequent time taken to flower in almost all genotype x growing environment combinations (the exceptions were plants of the cv. Maris Bead grown in three cooler, short-day regimes). The influence of temperature and photoperiod on the rate of flowering was quantified, using a model applied previously to other long-day species of grain legume in which positive linear relations between both temperature and photoperiod and the rate of progress towards flowering are assumed to apply. A significant positive linear response of rate of progress towards flowering to limited ranges of mean diurnal temperature was detected in all six genotypes, but in three genotypes (Syrian Local Large, Aquadulce and Maris Bead) the 28 °C day temperature reduced the rate of progress towards flowering - suggesting that the optimum temperature for flowering in these genotypes is below 28 °C. In four genotypes (Maris Bead, Giza-4, Aquadulce and BPL 1722) a significant positive response to photoperiod, typical of quantitative long-day plants, was observed only in plants grown from vernalized seeds. In contrast, plants of the genotype Zeidab Local grown from both non-vernalized and vernalized seeds showed the same positive response to photoperiod, whereas plants of the land-race Syrian Local Large were consistently unresponsive to photoperiod. The implications of this range of responses amongst diverse genotypes are discussed in relation to screening germplasm.