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Cereal yield and grain quality may be impaired by environmental factors associated with climate change. Major factors, including elevated CO2 concentration, elevated temperature, and drought stress, have been identified as affecting cereals production and quality.

Indeed, numerous effects of elevated atmospheric CO2 on plants have been documented to increase the activity of photosynthesis, including increased carbon assimilation and therefore plant growth. Since grains are predominantly composed of carbohydrates (mostly in the form of starch), it has been suggested that increases in starch concentrations can cause a dilution effect on other nutrients, including proteins, lipids, vitamins, and minerals.

The effect of elevated CO2 on photosynthesis is more pronounced in crops such as wheat and rice but less notable in maize. Some researchers claim that the variation could affect the level of protein in barley, rice, and wheat, with the reduction reported to be 15, 10, and 10%, respectively. We are finding similar effect on the dilution of minerals. Elevated CO2 has been reported to decrease mineral concentrations in barley grains (−6.9%), rice grains (−7.2%), and wheat grains (−7.6%). Studies found that the most affect minerals to elevation of CO2 would be Ca, Cd, Cu, Fe, Mg, Mn, P, S, and Zn, while B and Na were not significantly affected, and K could even be significantly increased.

In contrast to CO2, increased temperature and drought cause significant grain yield loss. Both drought and heat stress decreases starch content but increases grain protein and mineral concentrations.

During the last two decades, the air temperature has increased by 0.85 °C. In fact, annual average minimum temperatures in South Europe have increased over the last century by 1.5 °C. The most probable outcome of climate projections foresees increases of 1.8 to 4.0 °C by the end of the 21st century (2090–2099) relative to the period 1980–1999.

Heat stress is a major constraint to sustainable cereal production, with reductions in grain yield being associated with high temperatures during the reproductive or grain-filling stages in wheat and rice.

Indeed, high temperature primarily impacts the accumulation of starch in wheat grain, with accumulation beginning earlier than under cooler temperatures, the duration of its accumulation also being reduced, and the result is a greater concentration of protein in the grain. Grain protein and mineral composition are quality characteristics that can change due to high temperature, and they respond to changes in enzymes involved in starch and protein synthesis.

The activity of glutamate synthase was enhanced by heat stress, while sucrose phosphate synthase, sucrose synthase, and soluble starch synthase were significantly decreased.

Regarding grain nutritional value and within the three environmental factors, the increase in CO2 is possibly the more detrimental to face because it will affect cereal quality in every region of the world whereas the effect of drought and elevated temperature will be limited to the regions affected by the changes.

Grain yield reductions mediated by drought have been widely reported in wheat and depending on the genotype, the reductions may reach up to 50%. In wheat, this smaller photosynthetic area and accelerated leaf senescence limit the amount of assimilates translocated to the grain, which implies reductions in grain yield. Grain composition is also affected. Drought stress affects starch accumulation more severely than protein accumulation during grain filling.

Once the concepts above explained, I would like to share with you a recent analysis done on the cereals harvested this year in France. The conclusion illustrated below are actually contradicting the physiological pathways presented above, which demonstrates that the mechanisms involved as more complex than that.

Indeed, this summer 2022 has been one of the hottest and driest in European history which had consequences on the development and composition of the grains. In the graph below, we see a comparison of the average starch and protein level made on 115 wheat samples for the 7 past years. The starch level reached an historical level of 62.2% whereas the level of protein went down to only 10.5%. The moisture of these samples has been reduced by 2 points versus analysis made last year from 13.8% down to 11.8%.

We noticed similar trend on the barley samples. The analysis presented below, made on 70 samples of barley harvested this year, shows a reduction of protein and moisture content compared to samples from 2021.

One of the consequences of these exceptional climatic conditions that we experienced that summer, was the reduction of mycotoxins contamination. On the 55 samples analyzed in the study, we did not detect the presentation of ZEA and/or DON in none of the samples (minimum detection for ZEA = 50ppb / minimum detection for DON = 220ppb). As reminder, in the same analysis made in 2021, 20% of samples were contaminated in DON at a level above 1,000ppb.

Like every topic related to climate changes, it is very difficult to foresee the consequences generated but it will inevitably affect our industry. The pressure on the production, the reduction of yield will certainly create some inflation on the prices and the change in the cereals composition will oblige nutritionists to review the way they are formulating. The center of cereals production may change to region less affected by the climate changes. But the selection of new genotypes of cereals more resistant to elevated temperature and drought could change that trend. That is definitively a topic that our industry will need to monitor


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