Yield physiology of rice

Rice (Oryza sativa L.) is a staple food for more than 50% of the world's population, including regions of high population density and rapid growth. Rice is produced under both upland and lowland ecosystems with about 76% of the global rice produced from irrigated lowland rice systems. The objective of this article is to discuss growth and formation of yield components in rice during crop growth cycles. The yield components of rice are the number of particles per unit area, number of spikelets per panicle, weight of spikelet and spikelet sterility or filled spikelet. In addition, shoot dry weight, grain harvest index, and nitrogen (N) harvest index are also positively associated with grain yield. These yield components and yield associated parameters are formed during crop growth cycle. Growth cycle of the rice plant is divided into three stages. These stages are designated as vegetative, reproductive and spikelet filling or ripening. Yield potential of rice is formed or defined during these growth stages. Plant height, tillering (associated with panicle number), root growth, leaf area, and morphology are the main features of vegetative growth stage. In the reproductive growth stage particle development takes place. Booting and flowering are part of the reproductive growth stage. Particle size or spikelets per panicle are determined in the reproductive growth stage. Spikelet size or weight is determined during the spikelet filling growth stage. The reproductive growth stage is the most sensitive to biotic and abiotic stresses, followed by spikelet filling and vegetative growth stage. Recent advances in molecular linkage maps of rice and other developments of molecular biology offer new opportunities for improving rice yield components in favor of higher yield.