Total Grain-Arsenic and Arsenic-Species Concentrations in Rice as Impacted by Genotype and Water Management.

Recent studies have indicated that high soil arsenic (As) concentrations can result in decreased rice (Oryza sativa L.) grain yields and increased grain-As concentrations.  Low As-concentration in rice grain is especially desirable for populations ingesting high As-concentrations from drinking water and also consuming rice as a staple food.  The present study involved the testing of a collection of indica and japonica rice genotypes from the USDA World Germplasm Collection for grain-As concentration and speciation under two water-management systems, namely continuous-flood and intermittent-flood, on two soil-As treatments, namely a native soil (~5 mg As kg^-1) with relatively high As availability and an adjacent monosodium methylarsenate (MSMA) treated plot with a higher As concentration (~19 mg kg^-1).  The total rice-grain As (TGAs) and As-species concentrations of genotypes were evaluated with respect to rice-plant traits (including heading date, yield, and straighthead-susceptibility rating).  TGAs concentrations with the MSMA treatment were considerably higher than with the native-soil treatment.  The predominant forms of As extracted from the rice grain were the organic species, dimethylarsinic acid (DMAs^V), and inorganic As^III (iAs^III).  TGAs, DMAs^V and iAs^III concentrations were each significantly different by soil-As concentration, water management and genotype.  Compared to continuous-flood, the intermittent-flood treatment reduced TGAs concentrations by 59 and 51 % with the native and MSMA-treated soils, respectively.  In the native soil, DMAs^V concentration was considerably higher with the continuous-flood treatment, accounting for 64 to 40 % of total grain-As accumulation, whereas with the intermittent-flood treatment DMAs^V proportion was lower (46 to 1%).  The intermittent-flood treatment was successful in lowering potentially harmful iAs^III concentrations up to 47 %.  Lower TGAs, DMAs^V, and iAs^III concentrations were in general observed in the high-yielding and early-maturing genotypes.  This study demonstrates the potential of genotype selection in combination with water management to produce rice with acceptably low TGAs, DMAs^V and iAs^III concentrations.