Impacts of High‐Temperature Stress and Potential Opportunities for Breeding

Abstract

Solar energy is the primary energy source for almost all of the world’s ecosystems and drives primary production. Solar radiation is also the heat source for the earth and fuels optimum ecosystem functions. Incoming infrared radiation is retained within the atmosphere by heat-trapping gases such as carbon dioxide; this creates a natural greenhouse effect (Rogers 1990). The world’s industries discharge about 15 × 109 tons of carbon dioxide (CO2) into the atmosphere every year. About half of this amount is fixed by planetary photosynthesis, a quarter is devoured by the oceans, and another quarter is deposited in the atmosphere. Atmospheric CO2 is essential for maintaining temperatures that support life systems; without CO2 the average global temperature would be −18◦C (Abrahamson 1989; Surasinghe 2009). However, infrared irradiation absorption by CO2 and other greenhouse gases such as methane, nitrous oxide, and sulfur dioxide may cause warming of the earth’s climate. Global surface temperatures are predicted to rise by about 2–5◦C by the end of this century, leading to significant changes in crop productivity, water supplies, and associated economic value (IPCC 2007). An overall increase of 2◦C in temperature and 7% in rainfall would lead to an almost 8% loss in farm level net revenue. These changes are already occurring. For example, in India, rainfall has decreased in July, and greater rainfall has been recorded in August in key cropgrowing areas. Another major change is that the monsoon pattern has shifted westward; this confines the rainfall to certain pockets and may result in floods and, in turn, food shortages for many people. The effects of global warming on food security will likely be more severe in India than in other parts of the world. For a 2◦C rise in temperature, the reduction in gross domestic product (GDP) is 5%, and for the next 6◦C increase, GDP would be reduced 15–16%. In Haryana, wheat (Triticum aestivum L.) production declined from 4106 kg/ha in 2001 to 3937 kg/ha in 2004, and the maximum temperature during February and March (booting and grainfilling) rose by about 3◦C in the last 7 years (Gahukar 2009). In addition, water supply will suffer because of scant rainfall in the Himalayas. South Asia’s prime wheat-growing land—the vast Indo-Gangetic Plain, which produces about 15% of the world’s wheat crop—will shrink 51% by 2050 because of hotter, drier weather and diminished yields; this loss will place at least