Grain inorganic arsenic content in rice managed through targeted introgressions and irrigation management

Authors: Fernandez-Baca, Cristina; McClung, Anna; Edwards, Jeremy; Codling, Eton; Reddy, Vangimalla; Barnaby, Jinyoung

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2020
Publication Date: 1/25/2021
Citation: Fernandez-Baca, C.P., McClung, A.M., Edwards, J., Codling, E.E., Reddy, V., Barnaby, J.Y. 2021. Grain inorganic arsenic content in rice managed through targeted introgressions and irrigation management. Frontiers in Plant Science. https://doi.org/10.3389/fpls.2020.612054.
DOI: https://doi.org/10.3389/fpls.2020.612054

Interpretive Summary: Arsenic (As) exposure from rice consumption is a serious and growing concern as rice is a staple dietary crop for half of the world’s population and is cultivated worldwide. Rice has been identified as a major As exposure route for humans and is often the principal source of As where drinking water As concentrations are low. The objective of this research was to understand the role of combinations of QTL associated with grain iAs in the genotypic response to alternate wetting and drying and flood management. Our study revealed that both the number and combinations of iAs-affecting QTL significantly impacted grain iAs concentrations. Furthermore, longer drying periods to meet the same target soil volumetric water content resulted in lower grain iAs levels. Our study demonstrates that coupling AWD, or other water-saving irrigation management practices, with the selection of low iAs accumulating cultivars is key to reducing rice iAs exposure while maintaining crop productivity.

Technical Abstract: Arsenic (As) accumulation in rice grain is a significant public health concern. Inorganic arsenic (iAs) is of particular concern because it has increased toxicity as compared to organic As. Irrigation management practices, such as alternate wetting and drying (AWD), as well as genotypic differences between cultivars, have been shown to influence As accumulation in rice grain. A two-year field study using a Lemont×TeQing backcross introgression line (LT-TIL) mapping population examined the impact of genotype and AWD severity on iAs grain concentrations. The “Safe”-AWD (35 to 40% volumetric water content (VWC)) did not reduce grain iAs levels, while the more severe AWD30 (25 to 30% VWC) consistently reduced iAs concentrations across all genotypes. The TILs also displayed a range of iAs concentrations depending on genotype from less than 10 up to 46 ppb under AWD30 and from 28 to 104 ppb under Safe-AWD. TIL grain iAs concentrations for flood treatments across both years ranged from 26 to 127 ppb. Additionally, seven quantitative trait loci (QTL) were identified from the mapping population. A subset of eight TILs, selected based on their unique identified QTL combinations, and their parents were grown to confirm QTL controlling iAs levels in a more controlled greenhouse environment. Greenhouse study results confirmed the genotypic grain iAs patterns observed in the field; however, concentrations were higher under greenhouse conditions as compared to the field. In the greenhouse study, the number of days under AWD was negatively correlated with grain iAs concentrations. Thus, longer drying periods to meet the same target soil VWC resulted in lower grain iAs levels. We also found that both the number and combinations of iAs-affecting QTL significantly impacted grain iAs concentrations. Therefore, identifying more grain iAs-affecting QTL could be important to inform future breeding efforts for low iAs rice varieties. Our study suggests that coupling AWD practices with target soil VWC of greater than or equal to 30%, implemented over a longer period of time, with the breeding of low iAs accumulating cultivars, selecting for lines with QTL that negatively regulate grain iAs concentrations, will be helpful in mitigating exposure of iAs from rice consumption.