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ARS Home » Southeast Area » Stuttgart, Arkansas » Dale Bumpers National Rice Research Center » Research » Publications at this Location » Publication #349964

Title: Genetic and physiological relationships between grain arsenic and resistance to straighthead

item Pinson, Shannon
item Edwards, Jeremy
item HUESCHELE, D - University Of Minnesota
item TARPLEY, LEE - Texas A&M Agrilife
item ISBELL, CHRIS - Isbell Farms
item Green, Carrie
item SMITH, AARON - Louisiana State University

Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/19/2018
Publication Date: 10/16/2018
Citation: Pinson, S.R., Edwards, J., Hueschele, D.J., Tarpley, L., Isbell, C., Green, C.E., Smith, A.P. 2018. Genetic and physiological relationships between grain arsenic and resistance to straighthead. Rice Technical Working Group Meeting Proceedings. February 19-22, 2018, San Diego, California. Electronic Publication.

Interpretive Summary:

Technical Abstract: There is global concern regarding the amounts of arsenic (As) contained in rice grains and foods. The World Health Organization (WHO) recently set a CODEX limit of 0.2 ppm inorganic As in milled white rice, and a lower limit of 0.1 ppm was advised for baby food products. Arsenic is also toxic to plants, with rice straighthead disease being associated with As-toxicity. Plants have evolved mechanisms that reduce As toxicity, and increased resistance to rice straighthead disease may be due to regulation of As uptake, transport, sequestration/tolerance or a combination of all three to mitigate toxic effects from As. Each of these mechanisms could also be contributing to the wide (200-fold) differences in grain-As reported among rice accessions. Arsenic toxicity and grain-accumulation are of greater concern in rice than other grain crops because the redox conditions in flooded rice paddies makes soil-As more available for plant uptake. One method proposed that can reduce grain-As concentrations by about 10-fold is to produce rice without a flood for all or part of the production season, but this can increase pest damage and decrease yields. Because roots uptake As through phosphorus (P) and silica (Si) transporters, application of P and Si fertilizers have also been evaluated means of decreasing grain-As and straighthead severity. Our research has focused on identifying rice genes and physiological factors that can be exploited to reduce grain-As. A previous study of 1763 international accessions (the USDA Rice Core), identified some rice accessions with higher than average As concentrations in their grain (a.k.a. “grain-As Accumulators”) and others with low grain-As concentrations (a.k.a. “Excluders”). It appears that US rice breeding efforts have inadvertently decreased grain-As in that US cultivars released more than 30 years ago accumulated more grain-As than more recent US cultivars. Compared to global varieties with a similar intermediate maturity, modern USA cultivars have lower grain-As. A set of 16 rice accessions (8 Accumulators and 8 Excluders, including ‘Lemont’ and ‘Jefferson’) were selected for further study. When the Accumulators and Excluders were compared for As concentration and metabolism in leaves and roots under field and hydroponic conditions, data indicated that reduced grain-As concentrations were not due to reduced root uptake or root-to-shoot transfer rates, but were associated with more efficient sequestration of As in leaf vacuoles, a process that involves several sulfur (s) containing compounds. This raised the question of whether application of S-containing fertilizer to increase S in rice plants could be used to decrease grain-As by increasing As-sequestration. The effects of foliar application of MgSO4 fertilizer on grain-As and straighthead response were investigated. Initial evaluation of foliar fertilization applied at the booting stage to one-half of three production fields planted with the same hybrid appeared promising. However, a second year of study involving replicated field plots of multiple pure-line and hybrid cultivars, as well as a repeat conducted in the commercial fields showed that neither grain-As nor straighthead were reduced even in the plots treated twice (seedling and booting stage) with a higher rate of MgSO4 than that applied the previous year. Both inorganic and total As were evaluated in the grain, with neither showing a reduction due to foliar treatment with MgSO4. In contrast, grain-S concentrations did increase with treatment, indicating that the foliarly applied S did enter and transport through the treated plants. Relationships between grain-As, grain-P, grain-S, hull-Si, and straighthead resistance in rice were further investigated by identifying QTLs for each of these traits in a single association mapping population – the USDA Rice Minicore. T