Floret survival in wheat: significance of the time of floret initiation relative to terminal spikelet formation

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Abstract
SUMMARY: Wheat (Triticum aestivum L.) cv. Gamenya was grown in a Mediterranean type environment in two separate field experiments, to determine the effects of nitrogen application and date of seeding on floret survival. One treatment, intermediate in nitrogen level and sowing date, was common in both experiments. Rates and durations of spikelet initiation and durations of the floret initiation period were estimated. At maturity, yield and yield components were measured and occurrence of individual grains at each floret position on odd-numbered spikelets were recorded. The time of floret initiation relative to terminal spikelet formation and the subsequent occurrence of grain were examined.Florets developed first in spikelets 5-13 and last in spikelet 1. Added nitrogen hastened the initiation of florets but did not affect the number initiated; it also increased the numbers of grains per spikelet. In the last sowing date treatment, time to floret initiation decreased, but the sequence of floret initiation was unaffected.Numbers of florets and grains on tillers were less than on main shoots. Only about 28% of all florets initiated developed into grain.The main conclusion was that the florets which initiated before the terminal spikelet formed grain and those that initiated afterwards did not; we accordingly postulate that the vascular system between the rachis and the floret develops as the floret is initiated, but that after terminal spikelet formation, this is inhibited and further grains then fail to develop.

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