A study of floret development in wheat (Triticum aestivum L.)

Abstract

Plants of wheat (Triticum aestivum L.) cv. Aotea were grown at high or low nitrogen levels and in a natural photoperiod or continuous light. Starting 17-21 days from the double-ridge stage, eight plants from each treatment were sampled every 3 days until anthesis, and the two basal, the sixth, and the terminal spikelets were sectioned longitudinally. A developmental score was assigned to each floret and rates of development calculated. Continuous light hastened development but reduced the number of spikelets per ear, while high nitrogen delayed development but increased spikelet numbers. The number of florets initiated in each spikelet varied within narrow limits, but grain setting depended strongly on spikelet position and on treatment. Although florets were initiated in acropetal succession, the rate of development tended to increase up to floret 4 but then declined markedly. As a result grain setting was confined to basal floret positions, although the two basal spikelets developed so slowly that they contributed relatively little to grain yield. Distal florets degenerated almost simultaneously at or before ear emergence, but those in intermediate positions continued to develop until after fertilization in the lower florets. It is argued that the spikelet is an integrated system in which correlative mechanisms play a part throughout the development of the florets.