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Effect of High-Temperature Stress on Crop Productivity
Global warming has effects and consequences on all walks of life. An increase of 2°C in temperature could decrease the rice yield by about 0.75 t/ha and a 0.5°C increase in winter temperature could reduce wheat yield by 0.45 t/ha. In view of global warming due to climate change, temperatures of most regions of the world are increasing. Therefore, temperature may become the most important environmental factor regulating crop growth and production potential. Temperature in conjunction with day length affects all growth processes of crops, and even different cultivars of the same crop may differ in their response. Heat stress adversely affects plant growth and development and induces oxidative stress in plants. Heat stress adversely affects normal plant growth and development depending on the sensitivity of each crop species. Each crop species has its own range of temperature maxima and minima at different developmental stages beyond which all these processes are inhibited. The reproductive stage is on the whole more sensitive to heat stress, resulting in impaired fertilization, causing abortion of flowers. During seed filling, heat stress retards seed growth by affecting all the biochemical events and reduces seed size. Unfavorable temperatures may significantly affect the photosynthesis, respiration, water balance, and membrane stability of leaves. To combat heat stress, plants acquire various defense mechanisms for their survival, such as maintaining membrane stability and scavenging reactive oxygen species by generating antioxidants and stress proteins. Thermotolerance can be improved by the accumulation of various compounds of low molecular mass known as thermoprotectants as well as phytohormones. Exogenous application of these molecules has benefited plants growing under heat stress. Alternatively, transgenic plants overexpressing the enzymes catalyzing the synthesis of these molecules may be raised to increase their endogenous levels to improve heat tolerance. In recent times, various transgenics have been developed with improved thermotolerance having potential benefits for inducing heat tolerance in food crops. Updated information about the effects of heat stress on various food crops and their responses as well as adaptive mechanisms is reviewed here.
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