Variation in the Optimum Temperature for Rates of Seedling Emergence and Progress Towards Flowering Amongst Six Genotypes of Faba Bean (Vicia faba)

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Abstract
Times from sowing to emergence and to the appearance of first open flowers were recorded for six diverse genotypes of faba bean (Vicia faba L.) grown in 18 h daylengths at seven different constant temperatures between 15 and 30 °C. The optimum temperatures for the mean rate of seedling emergence and the rate of progress towards flowering varied amongst genotypes within the ranges 19·9—26·5 °C and 19·9—25·4 °C, respectively. There was no significant correlation between the optimum temperatures for emergence and flowering amongst the six genotypes tested (r = 0·514, P > 0·25). For both seedling emergence and flowering, positive linear relations were found between rate of development and sub-optimal temperatures, and negative linear relations between rate of development and supra-optimal temperatures. Despite absolute differences in the rate of progress towards flowering, the response to sub-optimal temperatures did not differ significantly amongst the six genotypes (P > 0·25). This was confirmed by re-analysis of earlier data. In contrast, the response to supra-optimal temperatures differed significantly (P < 0·005) amongst the six genotypes. They could be classified into two discrete groups which accorded with differences in optimum temperatures. Genotypes BPL 1722, Zeidab Local and Giza-4 had warmer optimum temperatures and greater sensitivity to supra-optimal temperatures than Aquadulce, Maris Bead and Syrian Local Large.