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 Shannong 505 with small grain yield potential, were used for investigating the responses of postanthesis photosynthesis, dry matter accumulation and allocation, and grain growth to source/sink changes. At the initial grain filling stage, Hesheng 2 was sensitive to source reduction leading to an increase of net photosynthetic rate (P_N) by 10 %; however, little effect of sink reduction was observed. In Shannong 505, P_N was obviously decreased by sink reduction, and changed a little after source reduction. At the rapid grain filling stage, Hesheng 2 was sensitive to both source and sink reduction resulting in the increase or decrease of P_N, respectively. However, the response of P_N in Shannong 505 to source/sink changes was similar to that in previous stage. The dry matter (DM) accumulation after anthesis was affected by source/sink changes. In Hesheng 2, the decrease in DM was higher than that in Shannong 505 after the same source or sink reduction. Source reduction caused a decrease in the allocation of DM to the sheath and stem, and promoted the reserve photosynthates to be reallocated to grain. The effect of sink reduction was contrary. The grain mass of Hesheng 2 was more easily regulated by source/sink changes than that of Shannong 505. The 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 spikelet. This revised version was published online in July 2006 with corrections to the Cover Date.