In order to elucidate the role of antioxidant responses in salinity tolerance in rice genotypes under salt stress, experiments were conducted using four rice varieties, including salt-sensitive BRRI dhan 28 and three salt-tolerant varieties BRRI dhan 47, BINA dhan 8 and BINA dhan 10. Thirty-day-old rice seedlings were transplanted into pots. At the active tillering stage (35 d after transplanting), plants were exposed to different salinity levels (0, 20, 40 and 60 mmol/L NaCl). Salt stress caused a significant reduction in growth for all the rice genotypes. Growth reduction was higher in the salt-sensitive genotype than in the salt-tolerant ones, and BINA dhan 10 showed higher salt tolerance in all measured physiological parameters. The reduction in shoot and root biomass was found to be minimal in BINA dhan 10. Chlorophyll content significantly decreased under salt stress except for BINA dhan 10. Proline content significantly increased in salt-tolerant rice genotypes with increased salt concentration, and the highest proline content was obtained from BINA dhan 10 under salt stress. Catalase and ascorbate peroxidase activities significantly decreased in salt-sensitive genotype whereas significantly increased in salt-tolerant ones with increasing salt concentration. However, salt stress significantly decreased guaiacol peroxidase activity in all the rice genotypes irrespective of salt tolerance. K+/Na+ ratio also significantly decreased in shoots and roots of all the rice genotypes. The salt-tolerant genotype BINA dhan 10 maintained higher levels of chlorophyll and proline contents as well as catalase and ascorbate peroxidase activities under salt stress, thus, this might be the underlying mechanism for salt tolerance

As the world’s population increases, demands on staple crops like rice (Oryza sativa L.) will also increase, requiring additional fresh water supplies for irrigation of rice fields. Safe alternate wetting and drying (AWD) is a water management technique that is being adopted across a number of countries to reduce the water input for rice cultivation. The impact of AWD on plant growth, yield and grain quality is not well understood. A field trial of AWD was conducted at Mymensingh, Bangladesh over two boro (dry) seasons using eight field plots, four under AWD and four continuously flooded (CF). This manuscript describes the results of check cultivar BRRI dhan28 which was replicated in 35–40 rows per plot giving a total of 140–160 replicates per treatment. A study on the soil solution concentration of many elements indicated that manganese, iron, zinc, and arsenic were different under AWD conditions compared to CF on a number of sampling time points, but did not show a pattern related to the AWD treatment. A survey of soil strength using a penetrometer detected a small, but statistically significant, hardening of the surface soil of the AWD plots. At harvest the shoot and grain mass was significantly greater for the plants grown under AWD (9.0-9.4% and 12.0-15.4%, respectively) with the plants grown under AWD having a greater number of productive tillers. Physiological examination in the first year showed that although AWD decreased (∼21%) leaf elongation rate (LER) of recently transplanted seedlings during the first drying cycle, subsequent drying cycles did not affect LER, while tillering was slightly increased by AWD and there was evidence of higher leaf abscisic acid (ABA) in AWD plants. In the second year analysis of six phytohormones revealed that AWD increased plant foliar isopentenyladenine (iP) concentrations by 37% while leaf trans-zeatin concentrations decreased (36%) compared to CF plants. The elemental composition of the shoots and grains was also examined. In both years AWD decreased grain concentration of sulphur (by 4% and 15%), calcium (by 6% and 9%), iron (by 11% and 16%), and arsenic (by 14% and 26%), while it increased the grain concentration of manganese (by 19% and 28%), copper (by 81% and 37%), and cadmium (by 28% and 67%). These results indicate that plants grown under safe AWD conditions at this site have an increased grain mass compared to plants grown under CF, and this may be partly due to a high number of productive tillers. AWD decreases the concentration of arsenic in the grains in this site, but it elevates the concentration of cadmium

One of cadmium’s major exposure routes to humans is through rice consumption. The concentrations of cadmium in the global polished (white), market rice supply-chain were assessed in 2270 samples, purchased from retailers across 32 countries, encompassing 6 continents. It was found on a global basis that East Africa had the lowest cadmium with a median for both Malawi and Tanzania at 4.9 μg/kg, an order of magnitude lower than the highest country, China with a median at 69.3 μg/kg. The Americas were typically low in cadmium, but the Indian sub-continent was universally elevated. In particular certain regions of Bangladesh had high cadmium, that when combined with the high daily consumption rate of rice of that country, leads to high cadmium exposures. Concentrations of cadmium were compared to the European Standard for polished rice of 200 μg/kg and 5% of the global supply-chain exceeded this threshold. For the stricter standard of 40 μg/kg for processed infant foods, for which rice can comprise up to 100% by composition (such as rice porridges, puffed rice cereal and cakes), 25% of rice would not be suitable for making pure rice baby foods. Given that rice is also elevated in inorganic arsenic, the only region of the world where both inorganic arsenic and cadmium were low in grain was East Africa.

Growing demand for staple crops like rice will need to be achieved predominately through agricultural intensification and more efficient use of inputs. To meet this demand it is essential that the genetic diversity within rice is fully utilized. The aus subpopulation is considered an underappreciated resource within that diversity. A new rice panel, the Bengal and Assam Aus Panel (BAAP) of 266 aus accessions was generated with ∼2 million informative SNPs obtained using skim sequencing at ∼4× depth. The BAAP was grown in the field in Bangladesh in the ‘boro’ season under both continuously flooded and Alternate Wetting and Drying (AWD) irrigation during 2013 and 2014 in Mymensingh and during 2014 in Madhupur. Heading date, grain mass, straw biomass and harvest index were measured. The majority (94%) of BAAP accessions flowered within a relatively small window of 10 days. The AWD irrigation treatment generally caused an increase in grain mass, but no significant genotype by treatment interactions were detected for this trait. Shoot biomass was the only trait that showed evidence of genotype by treatment interaction. The average LD (Linkage Disequilibrium) decay across the genome was 243 Kbp. Genome wide association mapping revealed 115 quantitative trait loci (QTLs). There was little evidence of QTLs specific to the irrigation treatment, and only a few QTLs co-localized with known genes. However, some QTLs were detected across multiple sites and years. These QTLs should be targets for breeding, and include a region around 2.2 Mbp on chromosome 1, a large region in the middle of chromosome 7 and two regions on chromosome 11 (∼10 Mbp and ∼29 Mbp). The BAAP appears to be a valuable addition to the growing collection of GWA mapping populations of rice.