Effect of Photoperiod and Temperature on Flowering in Pea (Pisum sativum L.)

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Abstract
Six pea varieties, early to late flowering, were grown in 16 environments made up of all combinations of four mean daily temperatures (6, 12, 18 or 24°C) and four photoperiods (8, 12, 16 or 24 h). For the earliest variety, days from sowing to first flower was inversely proportional to temperature, and independent of photoperiod. Sensitivity to photoperiod in the other five varieties was temperature-dependent. At 24°C, all were photoperiod-sensitive, but at 6°C only the latest three varieties were sensitive. Flowering was most rapid at 24°C in 24-h photoperiod. However, the lowest node of first flower occurred in 24 h photoperiod, irrespective of temperature. The duration of the period from floral initiation to first flower was independent of variety and photoperiod. Thus, any differences in flowering between varieties arose prior to floral initiation. These differences are explained by three factors: different times to floral initiation in 24 h photoperiod, a photoperiod response in low temperature, and a photoperiod-temperature interaction. These factors are related to the flowering genes Lf, Sn and Hr and the 'units of maturity genotype'. The likely genotypes of the varieties are deduced from the reported action of these genes. Vernalization is interpreted in terms of high-temperature inhibition of flowering in short photoperiods. The effect of temperature on the relationship between node of first flower and days from sowing to floral initiation, and the influence of genotype and growing season on flowering time, are also discussed.