Influence of High Temperature and Breeding for Heat Tolerance in Cotton: A Review

Cotton (Gossypium spp.) is an important crop in several parts of the world, which is highly sensitive to environmental stresses. In the last century, carbon dioxide concentration [CO2] has risen rapidly from about 350 μmol mol−1 in 1980 to about 378 μmol mol−1 at present. At the current rate of gas emissions and population increase, it is predicted that CO2 will double by end of this century. These changes in CO2 and other greenhouse gases are predicted to increase surface mean temperature in the range of 1.4–5.8 °C. In addition, studies also show that future climates will have more frequent short episodes of high temperature (heat). Most crops are highly sensitive to heat stress and often result in progressively decreasing yields at temperatures above the optimum. In most of the cotton‐producing regions, current temperatures are already close to or above the optimum temperature for its growth and yield, particularly during flowering and boll growth period. Therefore, any increase in mean temperature or episodes of heat stress will further decrease yields. One of the most important and economic ways to overcome negative effects of heat stress is to identify and/or develop heat‐tolerant cultivars. At present, the major constraint for identifying heat‐tolerant cultivars is the lack of reliable screening tool. Better understanding of the possible impact of high‐temperature stress on physiological, morphological, and yield processes would not only help in mitigating the adverse effects of high‐temperature stress but also in developing reliable field‐screening tools. This chapter reviews effects of high temperature on the cotton plant as a whole, including important physiological, growth and yield processes, and fiber properties. In addition, various new screening techniques based on physiological, ecophysiological, and morphological traits to identify tolerant germplasm are discussed in detail. Finally, the genetic, biotechnological, and breeding approaches are discussed herewith to improve understanding of heat tolerance in cotton.