Development and Control of the Number of Flowers per Node in Pisum sativum L.

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Abstract
Non-dormant flower initials are laid down in the axils of successive leaf initials as they are formed by the apical meristem of Pisum sativum L. In cultivars with a maximum capability of two flowers per raceme, the undeveloped flower meristem divides into two portions. One forms the first flower and the other either develops into a small protrusion on one side of the first flower or becomes the second flower, depending on the prevailing environment. Flower development in conditions favouring single-flowered racemes was advanced by one plastochron. Variation in the number of flowers per raceme occurs between cultivars and between environments. The number of double flowers formed was favoured by higher light intensity (120 Js−1 m−2) and carbon dioxide concentration (330 μ11−) and lower temperature (15°C). In cultivars producing more than two flowers per raceme, lower light intensity (60 Js−1 m−2) plus higher temperature (20°C) increased the mean number of flowers per raceme. Soluble sugar levels in all varieties were higher (36.05 mg eq glucose g−1 fresh weight) in the low temperature/high light environment than the high temperature/low light environment (14.80 mg eq glucose g−1 fresh weight). The flowering potential and stability of 13 cultivars have been assessed in controlled environment and in sowing date trials in the field. A stable variety, which consistently produced two flowers per raceme, was identified in controlled environment and its stability was maintained in field trials. A linear regression of stability of flower number in the field on stability in controlled environment accounted for 89.6 per cent of the variance (P<5 per cent), but the flowering potential in a sowing date experiment was not related to temperature or radiation intensity.