Assimilate Supply and Floret Development Within the Spike of Wheat (Triticum aestivum L.)

Abstract

The effect of increased as well as reduced assimilate on floret growth and development in wheat (cv. Yecora) was investigated in a controlled environment. Plants from which all tillers were removed were grown at 21/10°C with a 14 h photoperiod. At flag leaf emergence, an additional light (15% above control) and two shading treatments (40 and 70% below control) were applied to the plants for an 8-day period, ending 6 days before anthesis. The additional light and the 70% shade treatments had significant effects (+37%, -43% respectively), on the number of competent florets (as judged by anther appearance at anthesis) and subsequently similar effects on the number of kernels per spike at maturity. The changes in competent floret numbers were closely related to changes in spike dry weight at anthesis and in turn, during the treatment period. The heavy shading decreased grain yield significantly. Within the spike, treatment effects on floret and kernel number were greater in basal spikelets than in distal and especially central spikelets, in both an absolute as well as relative sense. These effects were paralleled by greater changes in basal spikelet dry weight and water-soluble carbohydrate concentration. They may be related to the smaller size or later development of basal spikelets at the onset of treatment, and suggest that the base of the spike is normally a lower priority sink for assimilate at that time.