1. Conserve, regenerate, characterize and expand rice germplasm and blast fungal collections to provide new genetic resources for rice research. 1A. Conserve and characterize the current NSGC rice collection through phenotypic and genotypic analysis to provide true to type and viable genetic resources for distribution to the research community. 1B. Determine the allelic value of Tropical japonica germplasm for improving US rice cultivars. 1C. Identify new sources of germplasm and associated alleles that result in increased grain yield under AWD management system and growing conditions of the southern U.S. 1D. Characterization of agronomic and physiological performance of weedy (red) rice germplasm biotypes in AWD management systems. 1E. Expand the NSGC collection with the development and characterization of an O. glaberrima/barthii and an O. rufipogon rice wild relative diversity panels and evaluate for agronomic and biotic stress tolerance traits. 1F. Characterize the rice blast fungus M. oryzae (Mo) collection for AVR genes and their response to changing climate and production practices. 2. Discover genomic regions and candidate genes/alleles associated with high yield, reduced environmental impacts, resistance to biotic and abiotic stresses, beneficial microbial interactions, and novel/superior grain qualities that are expressed across environments and management systems (GxExM) by developing and utilizing bioinformatics tools, high throughput phenotyping, and omics-driven analyses. 2A. Map QTLs for root architecture at the seedling stage… 2B. Identify QTL associated with quality production under AWD management… 2C. Evaluate three Chromosome Segment Substitution Line (CSSL) libraries… 2D. Fine map yield enhancing loci derived from O. rufipogon introgressions… 2E. Identify genomic regions associated with increased quality production in response to extremes in temperature. 2F. Identify genomic regions associated with increased quality production in response to biotic stress derived from O. sativa and its wild relatives. 2G. Fine-map and conduct candidate gene analyses for kernel fissure resistance (FR)… 2H. Identify genomic regions… 3. Identify optimum gene combinations using modeling of interactions between agronomic traits, reduced environmental impacts, biotic and abiotic stress tolerance, the plant-microbiome, and rice grain quality parameters that are expressed across environments and management systems (GxExM). 3A. Determine impact of reduced input systems on weed suppression. 3B. Identification and validation of effective QTLs for disease resistance… 3C. Determine the impact of AWD irrigation management… 3D. Determine the impact of abiotic stress… 4. Develop and deploy improved rice germplasm for production under existing and new management systems and for new market opportunities. 4A. Develop improved cultivars and germplasm for production in the southern U.S… 4B. Deploy yield enhancing loci derived from O. rufipogon introgressions… 4C. Determine if yield penalty is associated with disease resistance… 4D. Facilitate the development of new rice cultivars… Please see Project Plan for all listed Sub-objectives.
Rice is one of the most important cereal grains and it is important to sustain USA rice production for both domestic and global food security. A major challenge in rice production is diminishing irrigation resources. One approach being adopted uses alternate wetting and drying (AWD) irrigation that reduces water use by 20%. Yet there are many questions as to how to optimize quality production under this management system. In addition, record high temperatures during grainfill have resulted in yield and quality losses. This project will use genetic resources, genomic sequence data, and high throughput phenotyping to understand the genes and physiological processes that impact rice yield and quality under changing cultural practices and climates. The approach includes 1) exploring diverse genetic resources for novel traits and genes for developing improved rice cultivars that are resilient to changing climates and production practices, 2) identifying genes through mapping of quantitative trait loci (QTL), 3) identifying combinations of genes that result in increased yield and grain quality, and 4) developing and deploying unique combinations of genes in germplasm that will benefit the US rice industry. Central to the program is curation of the USDA’s world rice collection of over 19,000 cultivars. Subsets of this collection are used to create diversity panels that explore specific gene pools (e.g. O. glaberrima, O. rufipogon, Aus, etc.) for response to biotic and abiotic stresses. In addition, a collection of US rice blast (Magnaporthea oryzea) pathotypes will be evaluated for their ability to causes disease in response to different rice genotypes, management systems, and climatic environments (G x M x E). Segregating mapping populations developed from bi-parental matings and chromosome segment substitution lines (CSSLs) developed using wild species will be used to map QTL for response AWD and heat stress, yield production, disease resistance, kernel fissure resistance, and grain nutritional quality. Recombinant inbred lines (RILs) and CSSLs that possess QTLs for these traits will be used to determine which combinations of genes/QTLs provide the most robust response to production under systems using reduced inputs and having high disease and weed pressure as well as abiotic stresses such as drought and high temperatures. Although most of our previous research has focused on above ground traits, this project will include evaluation of root architecture traits and plant-soil-soil microbiome interactions that may be driving above ground phenotypes and responses. Outcomes from this research will include identification of unique germplasm, location of important QTLs, new methods for accurate and efficient phenotyping, and genetic markers linked to QTLs that can be used in marker assisted breeding. Our goal is to deploy improved germplasm that can be used directly as cultivars or as parental stocks in breeding programs that possess unique combinations of genes that provide high yield, superior milling and processing quality, are resilient to pest pressures and abiotic stress, and have unique nutritional quality that will result in high crop value.
Some 1200 world rice accessions were rejuvenated using summer and winter nurseries and were made available to the public through the National Plant Germplasm System. The Genetics Stocks Oryza collection provided seed of 2000 accessions to domestic and international researchers. Over 500 accessions in the tropical japonica core collection were phenotypically characterized and will be genotyped next year. New collaborative research was initiated to explore the potential for using drone imaging to phenotype the collection while growing in the field. The multiparent advanced generation intercross population was evaluated for heading, plant height, and panicle and flag leaf traits. A subset of 291 lines is undergoing more extensive phenotyping and will be genotyped to dissect genes underlying yield related traits. A second year of evaluating some 50 Aus cultivars under severe drought conditions was conducted to identify tolerant germplasm. Two accessions were identified as being extremely tolerant and were crossed with adapted U.S. cultivars to develop new mapping populations that are currently being advanced. Progress has been slowed in studies involving assessment of weedy red rice biotypes under reduced irrigation practices due to retirement of the project’s technicians in January 2019. However, one new technician was hired in July 2020. Phenotyping of the Africa Rice panel was completed as well as genotyping with currently available markers. Additional markers will be developed to fill in the gaps for conducting genome-wide association mapping with the panel. Additional wild O. rufipogon species complex accessions for the wild-RDP2 panel accessions were obtained and will be grown during FY21. A total of 30 rice blast isolates were selected based on avirulence gene sequencing, simple sequence repeat markers and pathogenicity assays. These isolates are available for breeders to use in screening new cultivars for blast resistance. Additional blast isolates collected from fields during 2015-2019 are being tested using genetic markers and an international differential system to assemble a new panel of isolates to evaluate diverse rice germplasm for new blast resistance genes. Several mapping populations and root evaluation methods are being used to identify genes affecting root size and architecture. Two of these populations were genotyped using the Cornell 7K Infinium Rice Array. A bioinformatics pipeline was created to process the genotypic dense data which imputes missing markers and bins adjacent markers to precisely define recombination breakpoints. Other bioinformatics scripts were written to facilitate downstream analysis and to visualize quantitative trait loci positions to reveal multi-trait effects and dissect the components of complex traits. Saturated genotypes were determined for two populations and root architecture data from one population was used for quantitative trait loci analysis, multi-trait Bayesian network analysis, and genomic selection of root trait extremes. The second population is being phenotyped for the same. A chromosome segment substitution population that was genotyped and phenotyped for root and shoot biomass traits was used to identify are seven chromosomal regions affecting arsenic uptake and, in a separate study, differences due to temperature effects on the concentration of phosphorus in leaves and grain is being determined. Two years of phenotypic data have been completed on a Cybonnet by Saber mapping population grown under reduced irrigation practices and will be used to identify chromosomal regions associated with abiotic stress tolerance. Three Cybonnet based chromosome segment substitution lines populations with 234 total lines were evaluated in a field study and will be used for gene mapping of yield components. Due to budget constraints, progress has been slowed on building a heat stress chamber to for evaluating germplasm. It is expected this will be completed in early FY21. With grant funding from the National Institute for Food and Agriculture through Marquette University ten quantitative trait loci for seedling cold tolerance were identified in two subspecies specific populations and seven of these were validated in two association mapping panels. Selected candidate genes in these regions will be subsequently validated. Budget limitations have delayed genotyping of the Wild-4 population being used for sheath blight mapping until FY21. A mapping population developed from cultivars Minghui 63 and M202 has been genotyped and evaluated with 9 blast isolates and 7 resistance loci were identified one of which gives resistance to 7 blast races. The genomic platform has been changed for fine-mapping chromosomal regions for kernel fissure resistance which has delayed progress. However, tissue samples of 300 progeny have been collected for DNA extraction and subsequent genotyping. From the mutant population of the variety Katy, 2000 lines were screened for physicochemical grain traits using high-throughput imaging systems and 43 putative mutants were selected and planted for seed increase and will used to confirm phenotypes. The ‘242’ x IR36M population is being used for the study of flavonoid biosynthesis genes. Molecular markers for two genes regulating the on/off expression of red and purple pigmented flavonoids were used to classify the mapping population into three color classes. Analysis of the purple class identified progeny having extremes in anthocyanin content. Genotyping identified a gene on chromosome 3 that regulates the intensity of bran anthocyanin. This population is also being used to study resistant starch content. Early generation inheritance studies indicate an additive effect of two genes affecting resistant starch as well as additional genes resulting in transgressive variation. Analysis of a second mapping population derived from KatyM by IR36M indicated that these two parents differ in mutations affecting resistant starch. Preliminary results suggest that the KatyM mutation resides in a region of chromosome 8 known to contain two starch-synthesis genes. It was hypothesized that genes affecting grain arsenic accumulation might also affect silica accumulation and/or resistance to straighthead disease. However, mapping of a diversity panel indicated that these three traits are likely controlled by independent genes. Accessions differing widely in grain arsenic and calcium were used to develop several mapping populations and seed from more than 6000 progeny have been prepared for grain element analysis. A population developed from the two cultivars PI312777-weed suppressive and Katy-non weed suppressive has been evaluated under alternate wetting and drying and flood management systems. A subset of 32 progeny are being evaluated under drought stress to evaluate plant stress responses, soil water status, yield, and yield components. As part of a National Science Foundation grant through Washington University two weedy rice mapping populations are being developed to identify genes associated with plant competitiveness. To determine the stability of blast resistance genes under reduced irrigation management 12 blast resistant germplasm lines are being examined under alternative wet and drying in field studies in two states. The study to evaluate the impact of water stress on plant biomass changes and soil microbial populations has been completed and drafted for publication. Studies to determine the impact of temperature stress on cultivars possessing the Wxa allele that impacts processing quality have been delayed due to resignation of support staff. These milestones will be deferred until year 4 of the project plan. The study evaluating reduced water management on cooking and sensory quality has been completed ahead of schedule and has been drafted for publication. A small panel of recombinant inbred lines having a combination of three major grain chalk quantitative loci was studied to identify the impact of high carbon dioxide and temperature on chalk formation. Phenotypic results are being confirmed currently. Similarly, another set of recombinant lines is being evaluated for response to elevated carbon dioxide in combination with reduced water management on yield and quality traits. The study will be repeated in year 3. A set of elite breeding lines possessing a variety of novel traits has been phenotypically characterized and pure seed produced. Evaluation of the panel for salt tolerance and anaerobic germination has been delayed until year 3 due to support vacancies.
1. Good tasting rice with high dietary fiber. Dietary fiber, which includes resistant starch (RS), is recommended for consumption to prevent chronic diseases. Rice varieties that have higher RS than are commonly found in US varieties have been identified and understanding how RS may impact cooked rice sensory quality and functional properties is important to consumers and food processors. ARS researchers in Stuttgart, Arkansas, and in New Orleans, Louisiana, evaluated cooked rice texture and rice functional properties of ten rice varieties that vary in RS. Trained panelists using descriptive sensory analysis determined that only one of 14 cooked rice texture attributes, roughness, was different between the high RS group of varieties and other US varieties. Moreover, in an evaluation of the functional properties few differences were found between the two groups of varieties. These results demonstrate the potential for increasing RS in US rice varieties that enhances the health benefits of cooked rice while having minimum impact on cooked rice texture or processing quality.
2. Identification of novel quantitative trait loci (QTL) controlling inorganic arsenic levels in rice. Rice grown under typical flooded paddies can accumulate arsenic (As) which is an element that naturally occurs in the soil. Because rice is such an important grain for feeding the world, As accumulation in rice grain is a significant health concern and inorganic arsenic (iAs) is of particular concern because it has increased toxicity as compared to the organic form of As. ARS researchers at Stuttgart, Arkansas, and Beltsville, Maryland, reported seven novel QTLs controlling iAs levels in rice and further documented that the number of days the crop was under alternate wetting and drying irrigation management was related to a decrease in grain iAs concentrations. Furthermore, both the number and combination of QTL significantly impacted grain iAs concentrations. This knowledge will inform plant breeders in an effort to minimize exposure to iAs from rice consumption by coupling irrigation management practices with the development of low iAs accumulating cultivars.
3. Genome sequencing of the heirloom U.S. rice variety Carolina Gold as an improved genomic reference for US tropical japonica rice. Most modern U.S. rice varieties have ancestry tracing back to a relatively narrow genepool of tropical japonica founder cultivars. Carolina Gold is a historically important founder variety that helped establish the US rice industry because of its excellent grain quality. Currently, the reference genome used for most rice genomics studies is a temperate japonica variety which may cause “blind spots” when used in analyses of U.S. tropical japonica varieties. To serve as a better reference genome for the U.S., ARS researchers in Stuttgart, Arkansas, Stoneville, Mississippi, and Ithaca, New York, in collaboration with researchers at the University of Georgia, Mississippi State University, and Cold Spring Harbor, New York, resequenced 166 varieties that represent USA rice breeding efforts over the last century. This dataset allowed characterization of patterns of genetic change across the time course of breeding and selection in the USA. These data resources will help breeders and geneticists discover the sequence changes that have led to important genetic gains and potentially recover useful genetic variation that was inadvertently lost through the bottleneck of selection to enrich future cultivar development efforts.
4. Identification of a novel rice blast disease resistance gene from weedy rice. Rice blast disease is difficult to control due to rapid occurrence of new virulent races. Searching for more effective blast resistance (R) genes from different genetic resources is essential to manage this disease. In a previous evaluation of rice germplasm, it was determined that the rice blast R gene, Ptr, confers resistance to several U.S. blast races except for one of the most virulent blast races, IB33. ARS researchers in Stuttgart, Arkansas, identified a minor amino acid variation encoded by the Ptr allele found in a weedy rice biotype that resulted in an altered Ptr protein conveying resistance to IB33. The R gene, PtrBHA, was mapped with three closely linked genetic markers. The genetic markers linked to this novel resistance gene can be used to deploy resistance to this race of blast that currently does not exist in any U.S. cultivars.
5. Draining rice fields immobilizes naturally occurring arsenic in the soil and reduces its availability for rice uptake. Arsenic (As) which is an element that naturally occurs in soils, can be easily absorbed by rice plants when they are grown in flooded paddies and can result in significant levels of As in rice grain that may present a risk to humans that consume rice as major part of their diet. Draining of rice fields during the vegetative stage of plant growth has previously been reported as an effective cultural practice in reducing the accumulation of As in rice grain as compared to rice produced in saturated, flooded soils. ARS researchers in Stuttgart, Arkansas, along with researchers at Cornell University conducted a study that found that manganese (Mn) and iron (Fe) ratios in paddy soils impact the dissolved concentration of As in soil pore water. A single severe soil dry-down was effective in reducing As in the porewater for about a month due to the formation of iron and manganese oxides that immobilized the As. The biggest decrease in As availability occurred in the top 4 inches (10cm) of soil where field draining had a greater effect on soil drying and where the roots are more concentrated, than at a depth of 10 inches (25 cm) where soil moisture and availability of As, Mn, and Fe in the pore water changed less with field draining. This research demonstrates why soil dry downs during alternate wetting and drying irrigation management are effective in reducing As availability for rice plant uptake and is a cultural means to enhance the nutritional value of the rice crop.
6. Weedy rice relatives harbor novel sheath blight disease resistance genes. Rice sheath blight disease is one of the most devastating diseases of rice and causes significant yield losses worldwide because no source of complete resistance has been found. ARS researchers in Stuttgart, Arkansas, in collaboration with University researchers in Missouri and Massachusetts, with support from the National Science Foundation, evaluated sources of weedy rice, a weed that commonly occurs in rice production fields and negatively impacts yield and quality, for sheath blight resistance. Nine regions of the weedy rice genome were identified that contain markers associated with sheath blight disease resistance. Four of the nine genetic markers are associated with the actual disease resistance response rather than disease avoidance traits like plant height or heading date. Three of these markers have never been identified before and offer unique sources of resistance for breeding new rice varieties that will result in increased economic returns for growers and less reliance on fungicides.
7. Rice plant developmental changes in shoot and root biomass drive changes in the soil microbiome. Interactions between crops and rhizosphere soil microbial communities play an important role in plant productivity, health, and growth. However, there is a lack of understanding of how plant traits, such as root and shoot biomass, and plant developmental stage may impact the structure of the soil microbial community. ARS researchers in Stuttgart, Arkansas, and Beltsville, Maryland, in collaboration with researchers from South Korea, conducted genomic sequencing to evaluate changes in the rhizospheric microbial community structure in response to changes in above- and below- ground biomass as the plants transitioned from vegetative to the reproductive stage. Species identified in this study that were correlated with increases in either root or shoot biomass were involved in nitrogen cycling (Anaeromyxobacter spp.) and methane production (Methanocella avoryzae.) or were other known endophytes (Bradyrhizobium spp.). Furthermore, many of the microbial community genes and their functions observed during heading, when belowground plant biomass is maximized, were representative of cell growth (e.g. carbohydrate and nitrogen metabolism), while functions correlated with physiological maturity, when aboveground biomass is peaked, were indicative of cell decay. This knowledge will inform future plant breeding efforts to optimize beneficial microbial populations that influence methane emissions and soil health.
8. Water conserving management practices in rice production do not negatively affect grain quality. Depletion of irrigation resources represents a threat to U.S. rice production. To conserve water, U.S. rice producers are adopting alternate wetting and drying water management (AWD) which allows the soil to dry to a predetermined level before re-irrigating the field. Thus far, careful management of AWD practices have been shown to be effective in saving water while maintaining grain yield, but information was lacking on how AWD impacts grain quality. ARS researchers in Stuttgart, Arkansas, conducted two AWD studies using seven rice varieties that are diverse in cooking properties based on grain amylose content and gelatinization temperature. Treatments that differed in the degree of soil moisture and the timing of draining the fields were used to compare to a continuously flooded control. Results demonstrated that the AWD treatments did not affect head rice yield, grain chalkiness, grain size, or grain cooking traits. This research demonstrated that AWD cultural management practices that save irrigation water do not negatively impact grain quality traits that are important to determining crop value.
9. Identification of candidate genes affecting the accumulation of manganese in rice grains. Manganese is an essential element for both animals and plants, with the grain mineral content of rice being especially important for human nutrition because rice contributes a high percentage of calories and nutrition in subsistence diets around the world. Unfortunately, manganese deficiency is common when plants are grown in water-logged soils, such as rice grown in flooded paddies. ARS researchers in Stuttgart, Arkansas, in collaboration with scientists in Texas, Delaware and the United Kingdom, identified six chromosome regions containing genes affecting the accumulation and concentration of manganese in rice grains. Fourteen of these candidate genes are reported to have functions predicted to impact root uptake or tissue-to-tissue transport of manganese or chemically similar elements. Identification of genes associated with the complex processes of nutrient uptake and transport in the plant and deposition in the rice grain, is crucial to the breeding of rice varieties having nutritionally dense grains as well as improved plant health.
10. Discovery of a basis for rice blast disease resistance stability in the Southern USA. Rice blast disease caused by the fungus Magnaporthe oryzae is one of the most devastating diseases for rice production in the Southern USA. Resistance (R) genes in rice can effectively prevent blast disease by detecting and responding to avirulence (AVR) genes in the fungus. These AVR genes are highly unstable causing rice cultivars with new blast R genes to become ineffective after several years of large-scale production, and then cultivars carrying different blast R genes must be developed. However, the underlying molecular basis this is unclear. ARS researchers in Stuttgart, Arkansas, in collaboration with researchers at the Noble Foundation and University researchers in Arkansas and Kansas, along with support from a USDA-AFRI Integrated Grant, analyzed molecular changes of eight AVR genes in 849 strains of blast collected from Southern USA rice production fields during 1959 to 2017. Molecular changes of M. oryzae AVR genes were correlated with which R genes were deployed in rice cultivars over time suggesting that rice R genes influenced the potential for blast epidemics. This knowledge will aid the development of more effective strategies to manage rice blast disease through deployment of new resistant varieties.
11. DNA markers enhance the searchability of the USDA rice world collection for genetic and trait diversity. The U.S. rice genebank is a treasure chest for plant breeders because of the phenotypic and genotypic diversity among the historical cultivars that were grown before modern breeding techniques were developed, as well as, cultivars that are grown in widely different ecosystems. Challenges faced in managing this collection of over 19,000 varieties include providing sufficient and accurate trait information to facilitate searching the collection, and controlling redundant accessions, seed mixtures, and mislabeled accessions, as well as identifying gaps in diversity. To help address these issues, ARS researchers in Stuttgart, Arkansas, used a new system that employs genotyping using a small panel of 24 markers that are trait-specific (TSM), used for fingerprinting (FPM), or are unique to subspecies. In addition, TSMs were used to validate phenotypic data for fragrance, pericarp color, grain cooking quality, resistance to rice blast disease, plant pubescence, and plant height of accessions in the collection. Discrepancies identified between genotypic and phenotypic data are useful for quality control during curation or may present opportunities for identifying novel genes among accessions, particularly for TSMs. In addition, over 2,000 accessions were classified by species, subspecies, and subpopulation utilizing a subspecies marker and FPM. The DNA marker panel was also adequate for differentiating among 100 important U.S. cultivars, which are primarily derived from a narrow genetic background. As a result of this study, TSM and FPM descriptors will be added to the GRIN-Global database and will improve the accuracy and breeding value of the U.S. rice germplasm collection and provide new opportunities for gene discovery.
12. Six rice gene mapping populations are developed for incorporating novel genetic variation from a wild ancestral species into U.S. rice varieties. Rice was domesticated from the wild ancestral species, O. rufipogon, which harbors a wealth of ancestral genes that were lost during the domestication process. ARS researchers in Stuttgart, Arkansas, along with researchers at Cornell University and Chungnam National University, South Korea have developed a set of genetic mapping populations that will serve as a means of incorporating these ancestral genes back into cultivated rice that may offer previously unexplored opportunities for developing new varieties that are tolerant to biotic and abiotic stresses. Cultivated rice, O. sativa, has diverged into the two varietal groups, Indica and Japonica. Six different Chromosome Segment Substitution Line (CSSL) populations were developed from crosses between each of three diverse O. rufipogon accessions originating from China, Laos and Indonesia with a Japonica variety, Cybonnet, developed in the USA and an Indica variety, IR64, developed in the Philippines. Each population consists of progeny that possess small chromosome segments from the O. rufipogon donor parents in the background of the either Cybonnet or IR64, both of which are well adapted for production in the USA. These rice lines can be used by breeders to identify novel genetic variation from the wild ancestral species, O. rufipogon, and easily incorporate the desired gene(s) or trait(s) into locally adapted, elite germplasm for the development of new high yielding, resilient rice varieties. In addition, these populations are a powerful genetic resource for systematic dissection of agronomic, physiological and developmental traits in rice.
13. Discovery of chromosomal regions associated with rice sheath blight disease resistance in global rice varieties that are independent of undesirable plant architecture traits. Sheath blight disease is one of the most damaging rice diseases worldwide, reducing grain yields up to 50%. While some cultivars are more susceptible than others, none are known to be immune, and thus, there is a need to identify additional genes to further improve natural sheath blight resistance in modern rice cultivars. Unfortunately, many resistance genes currently reported are associated with undesirable plant architecture traits like excessive plant height, late maturity, and lodging susceptibility. To identify rice germplasm harboring resistance genes (QTLs) not confounded by plant architecture traits, ARS researchers in Stuttgart, Arkansas, in collaboration with researchers at Guangxi Academy of Agricultural Sciences in Nanning, China, evaluated a diverse collection of over 350 global cultivars for sheath blight resistance and agronomic traits under greenhouse and field conditions. Results identified ten potential genes for sheath blight resistance that were not associated with the undesirable plant traits and high levels of resistance were identified in cultivars having at least four of the ten resistance genes. This indicates breeders will be able to increase resistance to sheath blight through stacking several of these genes from global rice into new varieties adapted to the USA.
14. Use of molecular marker forensics to determine the origin and dispersal patterns of weedy red rice in Taiwan and USA rice production fields. Weedy red rice is a troublesome weed in rice production systems that can greatly reduce yields, quality, and market value of rice. Using a molecular research approach, ARS researchers in Stuttgart, Arkansas, in collaboration with researchers at the Taiwan Agricultural Research Institute, helped determine the source of weedy red rice in Taiwan commercial production fields that was causing significant economic losses for farmers. Molecular markers were used to analyze several hundred weedy red rice biotypes found in rice production fields that led to an understanding of their genetic origins and dispersal patterns. The use of contaminated seed sources and contaminated seed production fields were found to be the major source of weedy red rice in commercial production. Many of the weedy red rice biotypes were found to have originated from heirloom varieties of rice with red-bran seeds that had been cultivated on Taiwan farms in the distant past. These findings provided new insights into how to manage this weed in Taiwan rice production fields which is in stark contrast to the basis of weedy red rice infestations in rice fields in the southern USA where there is no history of growing red-seeded rice varieties or using transplant seeding systems.
15. Seeding rates affect rice growth, grain yield, and economic returns in organic systems. The market demand for organically produced rice is greater than what is currently grown in the USA. One of the biggest production constraints in organic rice is yield losses due to weed pressure since synthetic herbicide use is prohibited. ARS researchers in Stuttgart, Arkansas, in collaboration with university researchers in Texas, Arkansas, Connecticut, and Minnesota, conducted a study to determine the optimum seeding rate to use in organic rice production systems as a means of decreasing weed pressure and maximizing economic returns. Yield linearly increased with increased seeding rates and economic models were used to determine the optimum seeding rates for inbred and hybrid cultivars to maximize economic returns. These results contribute to filling the knowledge gap of how to optimize organic rice production practices and provide a reference to develop improved management strategies for growers.
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