MicroRNAs (miRNAs) play important roles in regulating salt tolerance in Dongxiang wild rice (DXWR, Oryza rufipogon Griff.). The development of salt-responsive miRNA-simple sequence repeat (SSR) markers will significantly bolster research on DXWR, providing novel tools for exploring salt-tolerant genetic resources and advancing the development of salt-tolerant rice varieties. In the present study, a total of 137 miRNA-SSR markers were successfully developed, specifically derived from miRNAs responsive to salt stress in DXWR. Subsequently, a subset of 20 markers was randomly selected for validation across three distinct DXWR populations, along with 35 modern rice varieties. Notably, 13 of these markers exhibited remarkable polymorphism. The polymorphic markers collectively amplified 52 SSR loci, averaging four alleles per locus. The polymorphism information content values associated with these loci spanned from 0.23 to 0.70, with a mean value of 0.49. Particularly noteworthy is the miR162a-SSR marker, which demonstrated distinct allelic patterns and holds potential as a diagnostic marker for discriminating the salt-tolerant rice varieties from the non-tolerant varieties. This study provides a valuable tool for genetic analysis and precision breeding, facilitating the identification and utilization of valuable salt-tolerant genetic resources.

Thailand’s northeast (NE) region is an area of high-quality cultivated rice (Oryza sativa L.) production. However, an outbreak of weedy rice has recently spread throughout the region. Weedy rice is phenotypically and morphologically similar to cultivated rice, making identification difficult. The prospective management of weedy rice in the future will involve the study of its genetic diversity and population structure in this region. This study assesses the genetic diversity and population structure of 380 weedy rice samples in the northeast of Thailand through simple sequence repeat (SSR) markers. Thirty-one SSR markers generated 213 alleles with an average of 6.87 per locus and an overall genetic diversity of 0.723. Based on its geographic origin, weedy rice in the Southern NE are showed greater genetic diversity than that in the Central NE and Northern NE areas. The outcrossing rate in all regions was relatively high, with the highest being in the Southern NE at 9.769%. According to genetic distance analysis, the clustering of weedy rice samples in northeast Thailand was not associated with the geographic region. Neighbor-joining and principal coordinate analysis revealed that the 380 weedy rice samples fell into two major clusters. Cluster I contained three weedy rice samples and four wild. In Cluster II, 377 weedy rice samples were closely related to the four cultivated rice cultivars as well as brownbeard rice (Oryza rufipogon Griffiths) wild species. The results suggest that weedy rice in northeast Thailand may have originated as a cross between cultivated and wild rice, as seen in the closely related species, O. rufipogon. Overall, the findings of this study demonstrate the high genetic diversity of weedy rice in this region. Notably, some samples adapted, performing more like cultivated rice, which may be problematic for the future production of high-quality rice in this region. The prevention of weedy rice should, therefore, be given greater consideration in future studies.

Rice is consumed by nearly half of the global population and a significant source of energy and nutrients. However, rice consumption can also be a significant pathway of inorganic arsenic (iAs) exposure, thus requiring a risk–benefit assessment. This study assessed nutrient element (NE) densities in fifty-five rice types (white, brown and wild rice) marketed in the UK. Densities of essential NE were used to rank rice types in meeting daily NE targets under different consumption scenarios through a newly developed optimisation approach. Using iAs data from these rice types, we assessed the margin of exposure (MOE) for low (the UK) and high (Bangladesh) rice intake scenarios. Our results showed that brown and wild rice are significantly higher in many NE and significantly contribute to dietary reference value (DRV). Our modelling showed that switching to brown or wild rice could increase the intake of several essential nutrients by up to eight times that of white rice. Using rice consumption data for mid-to-high-consumption countries, we estimate that brown rice could provide 100 % adult DRV for Fe, Mg, Cr, P and Mo, and substantial contributions for Zn, Se and K. Our results show that the amount of rice primarily determines risk from iAs consumed rather than the type of rice. Therefore, switching from white to brown or wild rice could be beneficial, provided iAs concentration in rice is within the recommended limits.

Salt stress is a major abiotic stress affecting the productivity of rice crop worldwide. This study screened a set of 71 rice genotypes collected from coastal parts of Goa and Karnataka states in India for seedling stage salinity tolerance to identify genotypes alternative to standard salt-tolerant donors Pokkali, FL478, etc. Phenotyping for seedling stage tolerance was carried out under micro plots at an induced salinity of 12 dS/m. For haplotyping, 14 Saltol QTL linked simple sequence repeat (SSR) markers on chromosome 1 were utilized. On the basis of the response to salt stress, 10 genotypes were found tolerant, 16 moderately tolerant, 29 sensitive and 15 as highly sensitive. Among the SSR markers, marker RM10871 was the most polymorphic with a polymorphic information content of 0.90, exhibiting 14 different alleles followed by RM10793 (0.84) and RM3412 (0.80) with 8 and 7 alleles, respectively. These markers also exhibited high values for the effective number of alleles (Ne) and gene diversity (I). The haplotype analysis revealed that the allelic constitution of the Saltol region of 10 tolerant genotypes from our study varied in comparison to the reference tolerant check FL478. Further, the haplotype of three tolerant genotypes, namely, Goa Dhan 2, Panvel 1 and Goa wild rice (GWR) 005 appears to be completely different from the FL478 haplotype indicating tolerance in these genotypes is controlled by genomic region other than Saltol. These three genotypes with probable novel regions for seedling stage salt tolerance can be considered for enhancing salinity tolerance of rice cultivars.

Cultivated rice (Oryza sativa L.) was domesticated from the Asian wild species O. rufipogon. Compared with cultivated rice, wild rice has spikelets/seeds with long barbed awns. In order to evaluate the role of awns in wild rice, four seed groups with different awn lengths (full, half, quarter and no awns) were prepared, and the following seed dispersal movements were investigated under simulated natural conditions as observed in the tropical Asian habitat: (1) seed detachment from the parent plant; (2) falling angle of mature seed; (3) ability to slip into small spaces; (4) horizontal movement on the ground and (5) horizontal movement in water. As a result, awns were found to enhance the detachment of matured seeds from the panicles in the initial seed dispersal step. They regulated vertical orientation in the air, and the vertical form may enable seeds to squeeze to the ground. The awned seeds also showed advantages in horizontal movements on the ground and in the water. In most of the experiments, seeds with full awns showed the best performance for seed dispersal, suggesting that wild rice keeps long awns to survive under natural conditions. Since seed awning is dominantly controlled by wild functional alleles at several loci, wild rice may be able to prevent a drastic reduction of awn length.

Cultivated northern wild rice (NWR; Zizania palustris L.) has been bred and studied since the 1950s. One challenge facing researchers is the lack of storage options, due to the seed's unorthodox behaviour. This study evaluated varying storage temperature and moisture conditions for the maintenance of seed viability and dormancy breaking in Minnesota-grown NWR. First, seeds were placed in non-submerged, freezing storage (NSFS) for 12–26 weeks, then in submerged, cold storage (SCS) for 2 weeks. The addition of SCS increased germination (%G) relative to NSFS alone (<0.1% NSFS, 15% NSFS and SCS), indicating that NSFS does not kill seeds but also does not break seed dormancy. Next, the required length of SCS was evaluated by placing seeds in NSFS for 12 weeks and then in SCS for 2–14 weeks. A longer SCS period increased %G from 3 to 79%, at 2 and 14 weeks of SCS, respectively. Lastly, seeds were placed in NSFS, followed by SCS, at varying intervals over a 29-week period. Across lines, germination increased from 20 to 76% between 4 and 7 weeks of SCS, respectively, then plateaued. The results of this study indicate that NSFS could be used to store NWR seeds, but at least 7 weeks in SCS is required to overcome dormancy. Additionally, while NSFS did not break seed dormancy, physiological changes related to stratification processes were occurring in non-submerged, freezing conditions. Results also suggest that the genotypic variation in NWR could be utilized for selection to improve germination and storage viability.

Outdoor experiments were conducted at two locations in Minnesota to characterize the growth, development, and vegetative reproduction potential of giant burreed grown with and without wild rice. Giant burreed growth was influenced by environment more than the presence of wild rice. Shoots emerged from corms 2 to 3 wk after planting (WAP), and continued throughout the growing season. Giant burreed attained a maximum height of 135 cm with an average 36 shoots/plant. Rhizome production started 4 to 6 WAP, and continued throughout the growing season. Corm formation at the base of shoots started 8 WAP and continued throughout the growing season. Rhizomes grew to a maximum cumulative length of 2500 cm/plant spreading in all directions and produced up to 250 buds/plant. Corm and rhizome bud viability was 15 and 10%, respectively. These data suggest that giant burreed grown in wild rice should be controlled by 2 to 3 wk after emergence to prevent vegetative reproduction.

Climate change-induced events are causing salinization of many rice-growing areas, requiring the identification of new sources of genetic variation for salt tolerance in plant genetic resources since commonly grown cultivars are sensitive to salt. To identify the level of salt tolerance across a wide range of genotypes, we used a multivariate screening method using multiple growth and physiological traits simultaneously. For this purpose, four indica, two japonica and two wild rice genotypes were grown hydroponically under 40 and 80 mM NaCl stresses; fourteen different growth, qualitative and physiological traits, e.g. plant height, biomass, root and shoot elongation rates, and tissue ion accumulation, were recorded. In general, indica varieties performed better than both japonica and wild species. Our approach identified the existence of qualitatively different mechanisms of salt tolerance across the genotypes. For example, Pokkali, a salt-tolerant indica variety, displayed both ‘Na exclusion’ and ‘ion balance’ mechanisms, whereas PSBRc50 and IR58 showed only ‘Na exclusion’, and the Japonica genotypes Banikat and Nipponbare showed only ‘ion balance’. The results demonstrated that the tolerance is dependent on the level of stress and that this varies between genotypes; Nipponbare is moderately tolerant to 40 mM NaCl but not to 80 mM. We also suggest that the use of multivariate analyses can simplify the complex salinity tolerance picture and can effectively reveal the salinity tolerant genotype from a wide range of germplasm. The results reported here identify different physiological mechanism of tolerance across the genotypes and provide a sound basis for future studies examining their underlying molecular mechanisms.

The diet consumed by urban residents in modern China has become rich in saturated fats and cholesterol. In addition, the diet is high in carbohydrates from white rice and processed wheat starch. The aim of the present study was to determine the effects of replacing white rice and processed wheat starch with wild rice (WR) as the chief source of dietary carbohydrates. Rats fed with the diet patterned after the diet consumed by city residents of modern China showed elevated serum lipid levels comparable with rats consuming a high fat/cholesterol diet known to induce hyperlipidaemia in this species. Meanwhile, rats consuming the city diet with WR as the carbohydrate source suppressed the increase in serum TAG and total cholesterol, and the decrease in HDL cholesterol level. In addition, the rats fed the WR diet suppressed the build-up of oxidative stress by improving antioxidant capacity, increasing superoxide dismutase activity and reducing malondialdehyde concentration, both in the serum and liver. These findings illustrate that WR is effective in suppressing hyperlipidaemia and oxidative stress in rats even when the diet consumed is high in fat and cholesterol.

The interactions between water content and temperature on freezing and desiccation damage were examined for Zizania (wild rice) embryos at several stages of maturity. The water content of excised embryos was manipulated by flash drying at 35°C or room temperature to between 2.5 g H2O/g dw and 0.05 g/g. Embryos were then exposed to temperatures ranging from 5 to −50°C. Viability following the drying and cooling treatments was assayed by leakage of electrolytes and germination in culture. Viability of embryos decreased when embryos were dried below a critical water content. The critical water content was greatest for the least mature embryos. Critical water contents were also temperature dependent and increased with decreasing temperature. Even though the critical water content varied with developmental status and temperature, the water activity corresponding to the critical water content appeared to be constant at 0.90. The most mature embryos survived temperatures as low as −50°C while the least mature embryos survived only to −18°C. These trends were predicted by ‘phase diagrams’ based on the physical properties of water in embryos at different stages of maturity (Vertucci et al., 1994a). Our results confirm the earlier prediction that long term preservation of Zizania grains is possible at −20°C and the degree of success will be related to the maturity status of the embryos.

The desiccation tolerance of Zizania palustris seeds has been debatable, but recently it has emerged that survival to low moisture contents is a function of the temperature during dehydration. Survival of dehydration is greatest at 25–30°C and viability declines as the dehydration temperature is reduced. On the other hand, extended hydrated chilling (stratification) is required to break dormancy. The present contribution examines the ultrastructural condition of embryonic axes of Zizania palustris after dehydration at various temperatures, and following reimbibition and stratification. Axis cells sustained least damage when dehydration was carried out at 25°C and ultrastructural deterioration was more severe with lower temperatures during water loss. Damage sustained as a result of unfavourably low dehydration temperatures was visible when seeds were fixed from the dry state and was generally exacerbated during fully imbibed stratification. However, 25°C represented the optimum dehydration temperature; seeds that had been dried at 30°C also showed considerable ultrastructural disturbance when fixed from the dry state. This was largely reversed during fully imbibed stratification, although signs of the damage that had been sustained still persisted. These observations are in keeping with the germination behaviour of Z. palustris seeds dehydrated at temperatures above and below 25°C. The results are discussed in terms of the predominance of one of two mechanisms of membrane deterioration, depending on the dehydration temperature, which are probably not mutually exclusive. It is hypothesized that, at temperatures above 25°C, damage by free-radical-mediated events may predominate, whereas, at temperatures below the optimum, irreversible lipid-phase transitions may be the major factor resulting in membrane damage.

Lepidopteran stemborers (Chilo zacconius Bleszynski, Chilo diffusilineus de Joannis and Maliarpha separatella Ragonot) and diopsid flies (Diopsis spp.) are economically significant insect pests of rice in Burkina Faso. The objective of this study was to monitor damage trends and the pre-imaginal populations of these insects on two host plants, cultivated (Oryza sativa L.) and wild rice (Oryza longistaminata Chev and Roehr). The study was conducted over four consecutive rice crop seasons from 1999 to 2001 in three irrigated rice-growing locations in western Burkina Faso. Sampling of cultivated rice was conducted monthly in 1 m2 quadrates in 100 randomly selected farmers' fields. Data on wild rice were collected monthly from each of the three locations using 500 tillers that were plucked at random and dissected. Results showed that in the absence of a rice crop lepidopteran stemborers and diopsid flies are able to survive on O. longistaminata, which can host the pre-imaginal populations of these insects throughout the year. Damage caused on cultivated rice varied across farmers' fields, seasons and phenological stages of the plants. With 8% the highest average extent of ‘whiteheads’ was recorded during the dry season. These results are important elements in the design of a sustainable management strategy for these insect pests.

The African rice gall midge Orseolia oryzivora is a major pest of rice in Burkina Faso. The present study was carried out during four consecutive crop seasons from 1999 to 2001, in three rice-irrigated schemes, near Bobo Dioulasso town in south Burkina Faso. The fluctuation of immature stages of the pest and their damage, with regard to host plants was monitored. These included the cultivated rice Oryza sativa and its ratoons, and wild rice Oryza longistaminata. Sampling on growing rice was carried out monthly in 1m2 quadrats, in each of 100 randomly selected farmers fields. Sampling on rice ratoons was carried out after rice harvest and 500 tillers were randomly selected in the same fields and taken to the laboratory for dissection. Data on wild rice were collected every month by sampling and dissecting 500 tillers per site. This study revealed that in the absence of rice, the pest survived on rice ratoons and wild rice. However, cultivated rice was the preferred host plant as the crop recorded over 15% galling during wet seasons while damage was very low in dry seasons. Results from this study represent an important step towards the development of an IPM programme to control the rice gall midge, with regard to its host plant relationships.