POSTANTHESIS ALLOCATION OF PHOTOSYNTHATES AND GRAIN-GROWTH IN WHEAT CULTIVARS AS AFFECTED BY SOURCE SINK CHANGE/

Two wheat cultivars, Hesheng 2 with large grain yield potential, and S hannong 505 with small grain yield potential, were used for investigat ing the responses of postanthesis photosynthesis, dry matter accumulat ion and allocation, and grain growth to source/sink changes. At the in itial grain filling stage, Hesheng 2 was sensitive to source reduction leading to an increase of net photosynthetic rate (PN) by 10 %; howev er, little effect of sink reduction was observed. In Shannong 505, PN was obviously decreased by sink reduction, and changed a little after source reduction. At the rapid grain filling stage, Hesheng 2 was sens itive to both source and sink reduction resulting in the increase or d ecrease of PN, respectively. However, the response of PN in Shannong 5 05 to source/sink changes was similar to that in previous stage. The d ry matter (DM) accumulation after anthesis was affected by source/sink changes. In Hesheng 2, the decrease in DM was higher than that in Sha nnong 505 after the same source or sink reduction. Source reduction ca used a decrease in the allocation of DM to the sheath and stem, and pr omoted the reserve photosynthates to be reallocated to grain. The effe ct of sink reduction was contrary. The grain mass of Hesheng 2 was mor e easily regulated by source/sink changes than that of Shannong 505. T he effect source/sink changes on grain mass was in order upper > basal > middle spikelets on spike. As for a spikelet, the effect was found mainly in the grain mass at the positions 3 and 4 from base of the spi kelet.