Agronomic And Physiological Performance Of Annual Super-High-Yielding Wheat And Rice

Understanding agronomic and physiological performance of crop high yield is essential to make strategies for breeding and crop management. This study aimed to identify major agronomic and physiological traits associated with high grain yields of rice and wheat in the wheat-rice rotation system in the lower reaches of Yangtze River of China. Two high-yielding cultivars, each for winter wheat (Lianmai1) and rice (Liangjing6), were field-grown from2008to2010for three years. Two cultivation patterns, the local farmer’s practice (LFP) and super-high-yielding cultivation (SHC), were used. The SHC adopted two new key techniques, i.e., site-specific nitrogen management and alternate wetting and moderate drying irrigation in rice and controlled soil drying irrigation in wheat. Across the three years, SHC yielded an average9.67t hm-2of wheat and12.55t hm"2of rice with an annual total of22.2t hm-2, an increase of26.8%when compared with that (17.5t hm--) under the LFP. The increased grain yield under the SHC was mainly attributed to expanded sink size as a result of more kernels per spike, increased kernel weight of wheat and increased percentage of filled grains of rice. When compared with LFP, SHC showed a greater percentage of productive tillers, more pre-anthesis nonstructural carbohydrate (NSC) storage in the stem, greater leaf photo synthetic rate and concentration of cytokinins in root exudates, higher activities of sucrose synthase and adenosine diphosphoglucose pyrophosphorylase in grains, more dry mater production during the grain filling period, and higher harvest index. Pre-anthesis NSC in the stem and the amount of NSC per kernel (or spikelet) at anthesis were significantly and positively correlated with kernel weight of wheat and the percentage of filling grains of rice. The leaf photosynthetic rate and activities of both enzymes in grains were significantly and positively correlated with cytokinin concentration in root exudates. We conclude that1) expanding the sink capacity through an increase in kernel number per spike or spikelet number per panicle,2) enhancing grain filling efficiency by an increase in pre-anthesis NSC in the stem, and3) increasing post-anthesis dry mater production by an enhancement in root activity during grain filling should be considered as three major strategies for further increases in grain yields of wheat and rice in the lower reaches of Yangtze River of China.