Role of Crop Physiology in Understanding Mechanisms of Yield Formation Under Water and Heat Stress Conditions.

Crop physiology is the study of various fundamental plant physiological processes that finally integrate to produce crop biomass and yield. Crop productivity in current and future climates is dependent upon several environmental factors. Two most important environmental stresses limiting crop productivity are heat (high temperatures) and water (drought) stress. Understanding the effects of heat and water stress on yield formation is an essential step towards developing improved crop cultivars and efficient management practices. Crop physiology plays a critical on all aspects related to yield formation under stress. The three most important components of yield formation are number of reproductive structures (ears, panicles or pods) per unit land area, number of seeds (or kernels) per reproductive structure, and seed weight. Steps involved in yield formation include: tillering (or branching), formation of floral organs; processes leading to fertilization and seed-set; and seed filling. Physiological studies have shown that reproductive processes [panicle exsertion, viability of gametes (pollen and stigma) and process of fertilization] are highly sensitive to heat and water stress leading to fewer grain numbers and poor yield formation. In addition, heat and/or water stress occurring during seed filling lead to premature leaf senescence, decreases in duration and rate of seed filling leading to smaller seeds. Cultivars with greater reproductive success, continued carbon assimilation and increased partitioning of resources to seed under stress conditions have better potential for yield formation. Management practices that use water more efficiently (e.g. by improved transpiration efficiency or root growth) are better at forming yield under stress conditions. Overall, crop physiology plays a critical role in developing efficient genetic, soil and water management practices for improving crop productivity.