Cereal grains are the dominant source of cadmium in the human diet, with rice being to the fore. Here we explore the effect of geographic, genetic, and processing (milling) factors on rice grain cadmium and rice consumption rates that lead to dietary variance in cadmium intake. From a survey of 12 countries on four continents, cadmium levels in rice grain were the highest in Bangladesh and Sri Lanka, with both these countries also having high per capita rice intakes. For Bangladesh and Sri Lanka, there was high weekly intake of cadmium from rice, leading to intakes deemed unsafe by international and national regulators. While genetic variance, and to a lesser extent milling, provide strategies for reducing cadmium in rice, caution has to be used, as there is environmental regulation as well as genetic regulation of cadmium accumulation within rice grains. For countries that import rice, grain cadmium can be controlled by where that rice is sourced, but for countries with subsistence rice economies that have high levels of cadmium in rice grain, agronomic and breeding strategies are required to lower grain cadmium.

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The mineral concentrations in cereals are important for human health, especially for individuals who consume a cereal subsistence diet. A number of elements, such as zinc, are required within the diet, while some elements are toxic to humans, for example arsenic. In this study we carry out genome-wide association (GWA) mapping of grain concentrations of arsenic, copper, molybdenum and zinc in brown rice using an established rice diversity panel of ∼300 accessions and 36.9 k single nucleotide polymorphisms (SNPs). The study was performed across five environments: one field site in Bangladesh, one in China and two in the US, with one of the US sites repeated over two years. GWA mapping on the whole dataset and on separate subpopulations of rice revealed a large number of loci significantly associated with variation in grain arsenic, copper, molybdenum and zinc. Seventeen of these loci were detected in data obtained from grain cultivated in more than one field location, and six co-localise with previously identified quantitative trait loci. Additionally, a number of candidate genes for the uptake or transport of these elements were located near significantly associated SNPs (within 200 kb, the estimated global linkage disequilibrium previously employed in this rice panel). This analysis highlights a number of genomic regions and candidate genes for further analysis as well as the challenges faced when mapping environmentally-variable traits in a highly genetically structured diversity panel.

16 17 As the world's population increases, demands on staple crops like rice (Oryza sativa L.) will also 18 increase, requiring additional fresh water supplies for irrigation of rice fields. Safe alternate wetting 19 and drying (AWD) is a water management technique that is being adopted across a number of 20 countries to reduce the water input for rice cultivation. The impact of AWD on plant growth, yield 21 and grain quality is not well understood. A field trial of AWD was conducted at Mymensingh, 22 Bangladesh over two boro (dry) seasons using eight field plots, four under AWD and four 23 continuously flooded (CF). This manuscript describes the results of check cultivar BRRI dhan28 which 24 was replicated in 35-40 rows per plot giving a total of 140-160 replicates per treatment. A study on 25 the soil solution concentration of many elements indicated that manganese, iron, zinc, and arsenic 26 were different under AWD conditions compared to CF on a number of sampling time points, but did 27 not show a pattern related to the AWD treatment. A survey of soil strength using a penetrometer 28 detected a small, but significant, hardening of the surface soil of the AWD plots. At harvest the shoot 29 and grain mass was significantly greater for the plants grown under AWD (9.0-9.4% and 12.0-15.4%, 30 respectively) with the plants grown under AWD having a greater number of productive tillers. 31Physiological examination in the first year showed that although AWD decreased (~21%) leaf 32 elongation rate (LER) of recently transplanted seedlings during the first drying cycle, subsequent 33 drying cycles did not affect LER, while tillering was slightly increased by AWD and there was evidence 34 of higher leaf abscisic acid (ABA) in AWD plants. In the second year analysis of six phytohormones 35 revealed that AWD increased plant foliar iso-pentenyladenine (iP) concentrations by 37% while leaf 36 trans-zeatin concentrations decreased (36%) compared to CF plants. The elemental composition of 37 the shoots and grains was also examined. In both years AWD decreased grain concentration of 38 sulphur (by 4% and 15%), calcium (by 6% and 9%), iron (by 11% and 16%), and arsenic (by 14% and 39 26%), while it increased the grain concentration of manganese (by 19% and 28%), copper (by 81% 40 and 37%), and cadmium (by 28% and 67%). These results indicate that plants grown under safe AWD 41 conditions at this site have an increased grain mass compared to plants grown under CF, and this 42 may be partly due to a high number of productive tillers. AWD decreases the concentration of 43 arsenic in the grains in this site, but it elevates the concentration of cadmium. 44 45 Key words: Rice, alternate wetting and drying, arsenic, cadmium, pore water 46 48 between 35-60% of their dietary calorie intake (Fageria, 2007). Irrigated lowland rice systems 49 produce ~75% of global rice (Fageria, 2007). Producing high yield under irrigated systems requires 50 large quantities of water (Bouman, 2009). It is estimated that to produce 1 kg of rice gra...

For the world's population, rice consumption is a major source of inorganic arsenic (As), a nonthreshold class 1 carcinogen. Reducing the amount of total and inorganic As within the rice grain would reduce the exposure risk. In this study, grain As was measured in 76 cultivars consisting of Bangladeshi landraces, improved Bangladesh Rice Research Institute (BRRI) cultivars, and parents of permanent mapping populations grown in two field sites in Bangladesh, Faridpur and Sonargaon, irrigated with As-contaminated tubewell water. Grain As ranged from 0.16 to 0.74 mg kg(-1) at Faridpur and from 0.07 to 0.28 mg kg(-1) at Sonargaon. Highly significant cultivar differences were detected and a significant correlation (r = 0.802) in the grain As between the two field sites was observed, indicating stable genetic differences in As accumulation. The cultivars with the highest concentration of grain As were the Bangladeshi landraces. Landraces with red bran had significantly more grain As than the cultivars with brown bran. The percent of inorganic As decreased linearly with increasing total As, but genetic variation within this trend was identified. A number of local cultivars with low grain As were identified. Some tropical japonica cultivars with low grain As have the potential to be used in breeding programs and genetic studies aiming to identify genes which decrease grain As.