Impact Of Climate Change On Wheat Grain Quality
Authors: VANITA PANDEY, SNEH NARWAL, SEWA RAM, RINKI, OM PRAKASH GUPTA & PRIYANKA CHANDRA, KAMAL GANDHI

Agriculture is strongly influenced by weather and climate. The atmospheric CO2 and temperature affect plant growth and development and both have changed in recent past and are predicted to change further. Carbon dioxide has increased from 270 to 380 μ mol mol'1 since industrial revolution and is still increasing at the rate of 1.5 to 1.8 μ mol mol'1 yr'1. It is expected to be between 470 and 570 μ mol mol'1 by the year 2050 (IPCC 2007). The increasing levels of carbon dioxide in the atmosphere are predicted to cause warmer temperatures (especially the daily minima), changed patterns of rainfall, and increased frequency and severity of heat-stress episodes, together with decreased frost frequency and rising sea levels. Wheat (Triticum aestivum L.), the most important staple crop in the world, is mainly cultivated in the winter-spring seasons when warming is most likely anticipated. The increasing CO2 and consequent rise in temperature are the major factors affecting development and growth of wheat, thus most likely to influence wheat yield and grain quality (Ortiz et al., 2008 and Nasehzadeh et al., 2017). Most studies of impact of climate change on wheat production are related to yield, usually expressed in changes in weight per unit area. A second impact, much less studied, is how the quality of food is impacted by climate change. Quality is most frequently expressed in terms of protein content or starch content. The latter also has been suggested to relate to “dough quality” or “loaf volume”. The impacts have been categorized in two categories: impact of increased levels of carbon dioxide and impact of rising temperatures.

Effect of rising atmospheric carbon dioxide on wheat grain quality

Rising CO2 levels have been credited to enhance the grain yield in wheat, which in turn is due to the development of more number of grains (more ears per m2) rather than heavier kernels. The grains from CO2 enriched plants were also reported to have lower grain protein concentration. Bread making quality mainly depends upon the gluten content, its strength and extensibility. The proportions and properties of two main classes of storage proteins (glutenin and gliadin) are primarily responsible for grain processing quality. In particular, the gliadins are associated with dough viscosity and extensibility and the glutelins (a type of glutenin), with dough strength. The ratio of gliadin and glutelin and proportions of large glutelin polymers are therefore, widely used as indicators of dough strength. Both of these proteins are adversely affected by elevated CO2 conditions. Increased CO2 induces reduction in protein of wheat grains by 14% under high nitrogen treatment (N 100) and 9% under low nitrogen conditions (N 50). Gliadin was reduced by 20% and 13% and glutelin by 15% and 15% respectively under these conditions. Thus flour from high CO2 grown grains will have a diminishing baking quality (Blumenthal et al., 1993).

Elevated CO2 brought about higher starch content in wheat grains due to increase in carbohydrate translocation from the source (leaves and stem) to sink (grain). Elevated CO2 treatments brought about reduction in the concentrations of total and non starch lipids by 7.0% and 11.5% respectively while starch lipids were increased by 3.2%. Lipids are also essential for bread making quality, although they compose only 1.5%"3.5% of the total wheat grain mass. They are closely associated with starch granules and gluten proteins and are involved in the binding of gliadin and glutenin in gluten and gluten to starch within dough (Uprety et al., 2010). There may be an inverse relationship between increasing grain yield and decreasing grain protein in wheat, resulting in benefits for starch based industries, while protein based industries may suffer from future CO2 elevation.

Most of the nutrients in grains originate from redistribution from vegetative pools during grain filling. Carbon dioxide enrichment also causes alterations in the concentrations of other macro and microelements in the wheat grains, decreasing their nutritional value. Reductions in macro elements such as N, P, K, Na, Ca, Mg, and S due to CO2 elevation are consistent for different cultivars. Among the micro elements, the concentrations of Fe, Zn and Mn are predominantly reduced by elevated CO 2. This is probably caused by the dilution effect, induced by increased concentration of carbohydrates in grains (Högy et al., 2008). An overall decrease in essential elements due to CO2 enrichment is likely to aggravate the already acute micronutrient malnutrition in the world, however, the total quantity of mineral nutrients, accumulated in grains per hectare are still higher under high CO 2 due to increase in grain yield.

Effect of rising temperature on wheat grain quality

Increasing temperature accelerates the rate of maturation, causing increase in protein content and proportion of large starch granules thus, modifying the grain protein composition and dough quality as well. Initial increase in temperature of 15-30 ºC results in a modest increase in dough strength however the further increase of temperature results in a considerable loss of dough strength. This dough weakening also causes reduction of loaf volume and mixing time thus affecting the bread quality (Li et al., 2013). The gliadin component is more affected by increasing temperature causing decreased glutenin-to-gliadin ratio and the proportion of very large glutenin polymers (Moldestad et al., 2011).

Conclusion

The global climate change is not only affecting the yield but also altering the composition and grain structure of wheat grains. These changes are a threat to the application and end use product quality of wheat, also affecting the baking and chapatti making quality. Therefore, research should be more focused on the identification and development of climate resilient varieties to increase not only the yield but maintain the quality of wheat grain for better end use.

References:

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About Author / Additional Info:
VANITA PANDEY, RINKI and OM PRAKASH GUPTA are Scientist,
SEWA RAM and SNEH NARWAL are Principal Scientist at ICAR-IIWBR, Karnal;
KAMAL GANDHI is Scientist at ICAR-NDRI and
PRIYANKA CHANDRA is Scientist at ICAR-CSSRI, Karnal.