Authors: Pardeep Kumar1, Meenu Goyal2, Ritu Batra3 and Gayacharan4
1Division of Plant Quarantine,
4Division of Germplasm Evaluation, ICAR-National Bureau of Plant Genetic Resources, New Delhi-110012, India
2Department of Biotechnology, Central University of Haryana, Mahendergarh-123031, India
3Department of Genetics and Plant Breeding, Chaudhary Charan Singh University (CCSU) Meerut-250004, Uttar Pradesh, India
Wheat (Triticum aestivum L.) is the staple food to one third of the world population. It is cultivated under diverse environmental conditions varying from cool rain-fed to hot dry-land areas. In many wheat-growing areas of the world, high temperature stress is the major limiting factor for wheat production. Due to climate change, wheat experiences varying degree of heat stress at different phenological stages but reproductive phase is more sensitive to higher temperature than vegetative stage due to its direct effect on grain number and dry weight (Wollenweber et al., 2003). The required optimum temperature for wheat anthesis and grain filling is from 12 to 22°C (Tewolde et al., 2006) and each degree Celsius of further increase in global temperature reduced wheat production by 6% (Asseng et al., 2015). High temperature effect different stages of grain development and quality of wheat as -
Effect of high temperature on grain filling
Heat stress accelerates grain filling rate (GFR) whereas grain filling duration (GFD) is shortened For instance, 5°C increases in temperature above 20°C increased the GFR and reduced GFD by 12 days in wheat (Yin et al., 2009). In wheat, high temperature (>30°C) after anthesis reduced the rate of grain-filling (Al-Khatib and Paulsen, 1984)
Effect of high temperature on starch content
Starch accounts for ∼70% of wheat grain dry weight and starch accumulation was reduced when endosperms developed at elevated temperatures (Macleod and Duffus 1988). Starch accumulation in wheat grains could be reduced by over 30% at temperatures between 30°C and 40°C, with the most critical stage being in early grain filling (Stone and Nicolas, 1995).
Effect of high temperature on starch granule composition
High temperature at grain filling stage had a significant influence on the size of starch granule distribution in the wheat kernels. B-type starch granules found to be highly sensitive to high temperature during the grain-filling period. The number of B-type granules decreased in response to high temperature while that of A-type granules rose (Blumenthal et al., 1995)
Effect of heat stress of grain protein content
Heat stress affects the grain protein contents by reductions in starch deposition during grain filling stage (Stone and Nicolas, 1998). The grain protein content increases under heat stress but total grain protein content decreases because heat stress decreases grain yield (Daniel and Triboi, 2000 ).
Effect of assimilate supply on grain weight under high temperature
As increasing temperature hastens senescence, it is possible that reduced starch content at elevated temperature is due to deprivation of a supply of assimilates. Kobata et al. (2012) reported that increasing the assimilate supply to grains significantly increased the grain dry weight and total plant dry weight in the post-anthesis period under heat stress.
Effect of high temperature on grain yield
Grain number and weight contributes towards final grain yield and both are sensitive to elevated temperature. Stone and Nicolas, (1994) reported yield reduction up to 23% in response to high temperature above 32°C for as little as 4 days.
Hence, increase in temperature above ambient decrease the grain yield and ultimately grain quality. The yield losses of heat stress can be minimized by developing the heat-tolerant genotypes of the wheat.
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