|Islam, M. Rafiqul|
|Guerinot, Mary Lou|
Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2011
Publication Date: 12/5/2011
Citation: Norton, G.J., Pinson, S.R., Alexander, J., McKay, S., Hansen, H., Duan, G., Islam, M., Islam, S., Stroud, J.L., Zhao, F., McGrath, S.P., Zhu, Y., Lahner, B., Yakubova, E., Guerinot, M., Tarpley, L., Eizenga, G.C., Salt, D.E., Meharg, A.A., Price, A.H. 2012. Variation in grain arsenic assessed in a diverse panel of rice grown in multiple sites. New Phytologist. 193:650–664. doi: 10.1111/j.1469-8137.2011.03983.x. Interpretive Summary: Inorganic arsenic (Asi) in rice grain has been identified as a possible threat to human health, with risk being strongly linked to total dietary rice consumption and consumed rice Asi content. This study aimed to identify the range and stability of genetic variation in total grain arsenic (As) in rice. Six field trials were conducted, one each in Bangladesh and China, two in Arkansas, USA over two years, and two in Texas, USA comparing flooded and non-flood treatments, on a large number of common rice cultivars (300) representing the wide genetic diversity among international rice cultivars. Asi correlated strongly with total As among a subset of 40 cultivars harvested in Bangladesh and China, suggesting that less-costly analyses of total grain As can be used when making breeding selections. Grain As concentration within each field ranged between 3- and 34-fold and varied between rice subpopulations. Genetic variation at all field sites was a large determining factor in grain As, indicating cultivars low in grain As could be developed through breeding. The temperate japonicas exhibited low grain As as a subpopulation. Effects for year, location and flooding management were also statistically significant, suggesting that breeding strategies may have to take into account environmental factors.
Technical Abstract: According to the World Health Organization, more than half of the world’s population suffers from some form of nutrient deficiency, largely attributed to the relatively poor nutritional value of crop grains. With about half of the world’s people dependent on rice as their main food source, improving the nutritional value of rice grains could have a major impact on human health. Improving the nutritional value of rice grain means more than increasing content and availability of desired elements such as iron, copper, and magnesium; it can also mean reducing the content of anti-nutritional elements such as arsenic (As). Arsenic is generally higher in rice than in other crop grains, primarily because the anaerobic soil conditions associated with flooded rice paddies chemically changes the form of As in the soil, making it more available to plants. Therefore, it would be desirable to develop rice varieties that accumulate less As in their grains, whether by resisting root uptake, or by sequestering the As in non-edible portions of the plant, such as roots or leaves. The first step in breeding for a trait is to understand the genetic diversity for that trait available among germplasm collections and international rice varieties. This study evaluated the As content of 300 international rice varieties after they were grown under a total of six diverse field environments: a field in China where the soil is known to be high in As due to natural geological formation, a field in Bangladesh where high As in the soil and irrigation water are known to result in rice grain with unusually high in As content, two years of field production in Arkansas, and two fields in Texas, one managed as a flooded paddy, the other kept irrigated but not flooded. Arsenic in one of several organic forms is significantly less toxic to plants and animals than inorganic arsenic (Asi). Data on As versus Asi observed in rice grown in Bangladesh and China, showed that while the relationship between As and Asi differed between the two locations, within each location Asi levels could be predicted from As. This is important because laboratory analysis of Asi is more complex and costly than analysis of total As. The fact that Asi levels can be predicted from As data means that breeders can use less-costly As data to select for rice low in grain Asi. Genetic variation at all field sites was a large determining factor in grain As, indicating cultivars low in grain As could be developed through breeding. The temperate japonicas exhibited low grain As compared to the other ancestral subpopulations of cultivated rice. Effects for year, location and flooding management were also statistically significant, suggesting that researchers should control environmental factors as closely as possible when comparing rice genotypes or treatments for levels of grain Asi.