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Breeding Cultivars of Rice for a CO2-Enriched and Warmer World
Shimono, H. and Okada, M. 2013. Plasticity of rice tiller production is related to genotypic variation in the biomass response to elevated atmospheric CO2 concentration and low temperatures during vegetative growth. Environmental and Experimental Botany 87: 227-234.

Rice (Oryza sativa L.) is one of the world's most important cereals and has been adapted by breeders to a wide range of environments, extending from 35°S to 53°N in latitude and from sea level to more than 2000 meters in altitude, which achievements were noted more than three decades ago by Yoshida (1981), demonstrating the great potential that exists for developing cultivars that are adapted to widely varying environmental conditions.

What was done
Cognizant of people's concerns about possible CO2-induced climate change, Shimono and Okada (2013) write in their recent work that they "examined the contributions of genotypic variation to the tiller number and individual tiller growth of 24 rice cultivars in response to an elevated atmospheric CO2 concentration (control + 191 ppm) and a low air temperature (control minus 4.7°C) during 56 days of vegetative growth after transplanting." This work was conducted with plants grown in pots within sunlit temperature-gradient chambers at the National Agricultural Research Center of the Tohoku Region of Japan.

What was learned
In describing the results, the two Japanese scientists report they found that the total dry weight produced by the various cultivars in the CO2-enriched treatment ranged from a loss of 11% to a gain of 121% (Figure 1 below), while the total dry weight produced by the cultivars in the low temperature treatment ranged from a loss of 30% to a gain of 9%.

Figure 1. Scatterplot of the relationships between treatment (CO2-enriched) and control (ambient, or normal CO2) values of total dry weight. The regression line indicates the average CO2-induced increase in total dry weight for all 24 cultivars is 27%.

What it means
With the knowledge that the atmosphere's CO2 concentration will continue to rise for some unknown but significant period of time, and with climate models predicting that temperatures will continue to rise over the same time period, this study provides a huge hint about the huge potential to successfully breed rice cultivars that could be made to outperform even the most productive of those already in existence. It also suggests that the same would likely be true of other major food crops. And with Bruinsma (2009) indicating that the global demand for food, due to the increasing human population of the planet, could well rise by 70% by the year 2050, it would appear to be absolutely essential that such breeding efforts - directed towards all of the world's major food crops - commence as soon as possible.

Bruinsma, J. 2009. The resource outlook to 2050: By how much do land, water use and crop yields need to increase by 2050. In: Technical Papers from the Expert Meeting on "How to Feed the World in 2050." Food and Agriculture Organization, Rome, Italy.

Reviewed 7 April 2013