Effect of source-to-sink ratio on partitioning of dry matter and 14C-photoassimilates in wheat during grain filling

Increasingly, wheat (Triticum aestivum L.) is being grown in tropical environments, but there is inadequate information about the physiological processes limiting yield. In this investigation, the source:sink ratio was manipulated to examine the performance of source-sink interactions after anthesis and the factor(s) limiting grain filling in tropical conditions. Plants of three wheat cultivars, Cuba C-204, Candeias and IAC-60, were artificially modified to give different source:sink ratios. The treatments were: I, Control; II, all spikelets on one side of the spike removed; III, all spikelets removed except the four central spikelets of the spike; and IV, flag leaf blade removed. The distribution of dry matter between kernels and stem internodes was analysed at harvest in all three cultivars. Partitioning of C-14-photoassimilates was measured on three occasions after anthesis in the cultivar Cuba C-204. Modifications of source:sink ratio led to different patterns of allocation of dry matter between cultivars and sowing dates. The reduction in sink size in treatment II produced no significant change in the mass per grain in the January sowing, but this was enhanced in two cultivars in the November sowing. In treatment III, both mass per grain and translocation of C-14-photoassimilates declined, apparently due to feedback inhibition of photosynthesis. The participation of stem reserves in grain filling and the existence of genotypic differences in response to availability of photoassimilates were corroborated. The pattern of partitioning of dry matter observed in plants in this investigation suggests a source limitation, particularly during the November sowing. This pattern differed markedly from that in other studies, most of which have been made in temperate areas. (C) 1999 Annals of Botany Company.