Heat stress effects on the reproductive physiology and yield of wheat

Climate change is adversely affecting wheat yields as the associated rising temperatures damage its reproductive physiology. Heat stress affects wheat at various stages of growth, but flowering and reproductive phases are the most sensitive to high temperatures as flower opening usually occurs in cooler environments. Heat stress at meiosis causes ovule and pollen sterility along with anther dehiscence. During pollen development, temperatures >30°C cause pollen abortion. At anthesis, heat stress limits resource translocation to developing grain, resulting in small grain and low yields. During grain development, heat stress shortens the grain-filling duration and decreases starch and protein accumulation due to reduced activity of grain biosynthesis enzymes and impaired flag leaf assimilatory efficiency and stem reserve mobilization. The development of heat-tolerant wheat genotypes through screening, selection and breeding using genetic engineering, exogenous application of osmoprotectants and agronomic approaches is a high priority. This review discusses the impact of heat stress on flower development and fertilization, grain development and reproductive failure in wheat and outlines strategies (i.e. breeding and selection, genetic engineering, molecular breeding and management) to improve heat tolerance in wheat.