Abstract

Guohua Mi*, Fanjun Chen and Fusuo Zhang

Wheat grain yield can be limited by source, sink or by both. Inconsistency of the previous results reflects the interactions between genotypes and environments. In north China where the hot, dry wind was frequent during grain filling, new winter wheat cultivars with large grains suffer from loss of grain weight quite often because the grain filling rate (GFR) is low. In the present study, the carbohydrate assimilation and utilization was investigated to possible role of carbon assimilation and utilization in limiting grain filling rate by comparing two winter wheat cultivars, a large-grain cultivar Jing9428 (slow GFR), and a small-grain cultivar CAU3291 (fast GFR). It was shown that there was no significant difference in net photosynthetic rate and leaf area index during grain filling between the two cultivars. However, soluble sugar concentration in stems of Jing9428 decreased much more sharply than CAU3291 when the linear grain growth phase began suggesting an insufficient supply of photosynthates for grain filling. In grains, the ratio of starch to sucrose, glucose and fructose content of Jing9428 was significantly lower than CAU3291. It was suggested that insufficient photosynthate supply rather than weak sink strength was the main reason limiting grain filling rate of the largegrain type wheat cultivars in north China