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Two-line hybrid rice (Oryza sativa L.) production requires an environment-sensitive genetic male-sterile (EGMS) line in which sterility is induced by high temperatures (TGMS), long photoperiod (PGMS), or both (PTGMS). Later in the ricegrowing season, temperatures will lower, and TGMS lines can produce late tillers, which could form fertile panicles (self-pollination). This would reduce hybrid seed purity. The seeding rate of the EGMS line could minimize this issue because the higher the seed rate, the higher the plant density, which would reduce the number of late tillers. Two Arkansas TGMS lines, 801s and 811s, were tested with four different seeding rates (20, 30, 40, and 60 lb/ac). Plots were planted in a randomized block design with three replications at the University of Arkansas System Division of Agriculture's Rice Research and Extension Center (RREC) near Stuttgart, Ark. Tillers were counted from the three centermost rows of each 7-row plot to avoid border effects. The number of tillers was categorized as late tillers (no panicles exerted) and mature tillers (panicles exerted). The results showed that there is no significant difference in the number of late tillers among the seeding rates; thus, seeding rate does not significantly reduce late tillers for hybrid seed purification. There was a significant difference in the number of mature tillers between the 20 and 60 lb/ac rates. An optimum seed rate of 30 lb/ac is recommended for an ample number of panicles for hybrid seed production because there is no significant gain of mature tillers using the higher seeding rates. This could help reduce hybrid seed costs by avoiding over-seeding the EGMS lines while maximizing hybrid seed production yields. [ABSTRACT FROM AUTHOR]

Efforts have been made by the University of Arkansas System Division of Agriculture's Rice and Research Extension Center's (RREC) hybrid rice breeding program to develop hybrid rice (Oryza sativa L.) varieties that include environmentally sensitive male-sterile (EGMS) lines, cytoplasmic male-sterile (A) lines, maintainer (B) lines, and restorer (R) lines. As parental line development was being attempted, test crosses were also made to evaluate both parents and the experimental hybrids. Parents were planted as panicle rows to select based on phenotypes, while simultaneously being crossed with other parental lines to produce test crosses to be evaluated in 2022. Efforts for hybrid variety development with Provisia® and Clearfield® herbicide technologies were also attempted. Lastly, successful hybrid seed (F1) production of 13 hybrid combinations was achieved, which enables us to test these new hybrids in the Advanced Elite Line Yield Trials (AYT) and/or Arkansas Rice Variety Advancement Trials (ARVAT) across the state in 2022. [ABSTRACT FROM AUTHOR]

The Arkansas Rice Performance Trials (ARPTs) are conducted each year to evaluate promising experimental lines from the Arkansas rice breeding program and commercially available cultivars from public and private breeding programs. The ARPTs are planted on experiment stations and cooperating producer's fields in a diverse range of environments, soil types, and agronomic and pest conditions. The ARPTs were conducted at 4 locations during 2019. Averaged across locations, grain yields were highest for the commercial cultivars RT 7301, RT XP753, RT 7501, RT 7521 FP, DGL263, RT Gemini 214 CL, RT 7321 FP, Jupiter, Titan, and RT CLXL745. Cultivars with the highest overall milling yields during 2019 included: PVL02, CLJ01, Jazzman-2, ARoma 17, Jupiter, CL151, CL153, and CLM04. [ABSTRACT FROM AUTHOR]

To reflect the recent changes of the Arkansas rice industry and streamline the delivery of new and improved rice varieties to Arkansas rice growers, the medium-grain rice breeding project has expanded its research areas and breeding populations to include both conventional and Clearfield medium- and long-grain rice as well as hybrid rice. The newest elite breeding lines/varieties from collaborating programs, as well as lines with diverse genetic origins will be actively collected, evaluated, and incorporated into current crossing blocks for programmed hybridization. To improve the efficiency and effectiveness of the program, maximum mechanized-operation, multiple generations grown in the winter nursery, and new technologies such as molecular marker-assisted selection (MAS) are rigorously pursued. [ABSTRACT FROM AUTHOR]

The deleterious effects of high nighttime temperature (HNT) negatively impact the rice industry in Arkansas, the U.S. and the world resulting in lost income for rice producers and processors. Both grain yield and grain quality are affected by HNT, but the specific responses of many cultivars important to Arkansas producers have yet to be documented. Seventy-two rice varieties and advanced lines were planted in a field study on four different dates during two years (2018 and 2019) at the University of Arkansas System Division of Agriculture's Rice Research and Extension Center near Stuttgart, Arkansas. Grain yield, head rice yield, chalk, temperature and sunlight were measured and analyzed. The top ranked lines for grain yield, head rice yield, and chalk were determined in each of the 8 planting date by year combinations. The top ranked long-grain lines for yield included several cultivars adapted to Arkansas including Diamond, Jewel, Templeton and Francis. Varieties in the top ranked for head rice yield included Cybonnet, Chenierie, ARoma 17 and several Arkansas selections. Varieties with the lowest ranked chalk values were Cybonnet, ARoma 17, Templeton, CL172 and two Arkansas advanced lines. The high ranking long-grain lines are suggested as candidates for crosses and future development of new rice cultivars with stable grain yield and quality in both normal and HNT conditions. [ABSTRACT FROM AUTHOR]

The major focus of the Hybrid Rice Program in 2018 was to produce experimental hybrid lines by crossing newly developed male-sterile lines with elite cultivars/advanced lines. Moreover, two experimental hybrid lines will be evaluated in a 2019 Arkansas hybrid yield trial (ARPT). The hybrid breeding program successfully constructed a pipeline for production of male-sterile lines for the two-line hybrid system which includes populations from early through advanced generations. Development of parental material required for developing hybrid rice through the three-line hybrid system has also been expanded. [ABSTRACT FROM AUTHOR]

To reflect the recent changes of the Arkansas rice industry and streamline the delivery of new and improved rice varieties to Arkansas rice growers, the medium-grain rice breeding project has expanded its research areas and breeding populations to include both conventional and Clearfield medium- and long-grain rice as well as hybrid rice. The newest elite breeding lines/varieties from collaborating programs, as well as lines with diverse genetic origins will be actively collected, evaluated, and incorporated into current crossing blocks for programmed hybridization. To improve the efficiency and effectiveness of the program, maximum mechanized-operation, multiple generations grown in the winter nursery, and new technologies such as molecular marker-assisted selection (MAS) are rigorously pursued. [ABSTRACT FROM AUTHOR]

Yield is a quantitative trait that is controlled by genetic and environmental factors. La- Grue, a high-yielding long-grain rice cultivar developed by the University of Arkansas System Division of Agriculture has been used as a parent in the development of other elite rice cultivars. There is limited information on the genetics that give LaGrue its high-yielding advantage. The objectives of this study are to identify agronomic traits that give LaGrue its high-yielding potential and to identify quantitative trait loci (QTL)/genes associated with the yield traits. A third objective of this study is to develop two recombinant inbred lines (RIL) for use in genetic studies. Four cultivars including LaGrue, Bengal, Lemont, and Mars were tested in a field study done at the University of Arkansas System Division of Agriculture's Rice Research and Extension Center (RREC) near Stuttgart, Arkansas. Results from the study showed that LaGrue exceeded all three cultivars at number of seeds/panicle, number of primary panicle branches/panicle, and seed weight/panicle. We also developed two bi-parental populations by crossing LaGrue with Lemont and Mars for QTL mapping and RIL line development. The results from this study can be used in the development of rice cultivars through marker-assisted selection. [ABSTRACT FROM AUTHOR]

The Arkansas rice breeding program has the ongoing goal to develop new long- and medium-grain cultivars as well as specialty cultivars including aromatics and Japanese quality short-grains. Cultivars are evaluated and selected for desirable characteristics. Those with desirable qualities which require further improvement are utilized as parents in future crosses. Important components of this program include: high-yield potential, excellent milling yields, pest and disease resistance, improved plant type (i.e., short stature, semidwarf, shorter maturity, erect leaves), and superior grain quality (i.e., low chalk, cooking, processing and eating). New cultivars are continually being released to rice producers for traditional Southern U.S. markets as well as for emerging specialty markets, which are gaining in popularity with rice consumers. This report describes the progress of the long-grain and specialty rice pure-line rice breeding efforts at the University of Arkansas System Division of Agriculture. [ABSTRACT FROM AUTHOR]

Seventy-two entries including advanced lines were selected for their agronomic value and/or suspected tolerance to high nighttime temperature (HNT). Entries were planted on four different dates to analyze the effects of a range of environmental conditions on desired traits such as grain yield and grain quality. Air temperature above the plant canopy in the field was recorded hourly, and the correlation values between the number of hours above two critical thresholds [77 °F (25 °C) and 82.4 °F (28 °C)], four different yield measurements (grain yield, brown rice yield, milling rice yield and head rice yield) and chalk were obtained. Entries showing high yield, low chalk and high milling yield are presented. [ABSTRACT FROM AUTHOR]

Currently 4 rice breeding programs and cooperative extension activities utilize the molecular genetics laboratory at the University of Arkansas System Division of Agriculture's Rice Research and Extension Center (RREC) near Stuttgart, Arkansas. Much of the effort over the last 18 years has been devoted to the genotypic characterization of parental lines and progeny in the areas of new long-grain and medium-grain cultivar development, hybrid rice breeding, aromatic rice breeding, backcross populations, genomic mapping of specific traits, seed purification, and genetic fingerprinting. In 2018, genetic analysis was performed on 9 major projects for the rice breeding group involving DNA marker-assisted selection (MAS) for the important traits of cooking quality, aroma, rice blast disease resistance, plant height, leaf texture, and Clearfield technology. Eight other smaller projects were conducted for the breeding programs as well. The Molecular Genetics lab screened 3697 test samples and 292 DNA reference samples with up to 29 markers. The rice molecular analysis projects included parental materials, male sterile and restorer lines, selected F1 hybrid lines, and early and advanced generations of conventional breeding materials currently in development. In total, the lab generated 28,425 data points for the year. The work was accomplished using 75 DNA template plates, 347 polymerase chain reaction (PCR) plates, 72 runs on the ABI 3500xL to analyze simple sequence repeat (SSR) markers, and 171 PACE runs to analyze single nucleotide polymorphism (SNP) markers. [ABSTRACT FROM AUTHOR]

Successful large-scale hybrid rice seed production relies on developing suitable male-sterile lines. The University of Arkansas System Division of Agriculture's Rice Research and Extension Center, Hybrid Rice Breeding program developed a new environmental genic male sterile (EGMS) line for two-line hybrid rice production. The new EGMS line contains genes/quantitative trait loci associated with desirable phenotypic and cooking quality characteristics. It produces acceptable male-sterile seeds and has been tested for hybrid rice production. [ABSTRACT FROM AUTHOR]

Jewel is a new short season, high yielding, long-grain rice cultivar with the Pi-ta gene for blast resistance and the Cheniere cook type developed from a complex cross with many parents, some of which are: Katy, Newbonnet, Drew, Lebonnet, Starbonnett, LaGrue, Lemont, Wells, Radiated Bonnet 73, short strawed Starbonnet, Dawn, and Bluebonnet 50. Jewel has been approved for release, by the University of Arkansas System Division of Agriculture's Arkansas Agricultural Experiment Station, to qualified seed growers for the summer of 2020. The major advantages of Jewel are its blast tolerance, yield potential, high whole kernel rice milling yield, long kernel length, low chalk and L-202 cook type. Jewel is a non-semidwarf standard long-grain rice cultivar with lodging resistance approaching that of Roy J. Jewel is rated moderately susceptible to rice blast, sheath blight and false smut, and rated susceptible to bacterial panicle blight. [ABSTRACT FROM AUTHOR]

Hybrid rice production using the two-line system requires developing environment genetic male-sterile (EGMS) lines which become male-sterile in certain environmental conditions. An EGMS line contains genes that can be induced to express by temperature (TGMS), daylight (PGMS), or both (PTGMS). This study will determine (1) the genetic sources (TGMS, PGMS, PTGMS) of several Arkansas EGMS lines, (2) the environmental thresholds of each line, and (3) the optimum/absolute planting dates to induce full sterility of these lines in Arkansas. A total of eight EGMS lines are being tested including 4 lines designated as 236s, 801s, 805s, and 811s developed by the University of Arkansas System Division of Agriculture's Rice Research and Extension Center (RREC) near Stuttgart, Ark.; and 4 mutant male-sterile lines designated as GSOR 1, GSOR 2, GSOR 3, and GSOR 4 developed by the Dale Bumpers National Rice Research Center (DBNRRC-USDA-ARS) near Stuttgart, Ark. First, the lines were screened in growth chambers using different temperatures to identify the genetic source and environmental threshold for each line. Plants were tested at the heading stage for pollen sterility via the pollen stain method. Next, each line was planted in a randomized block design with 3 replications and 3 planting dates to determine the optimum planting dates at field conditions at RREC in summer 2017. The percentage of sterility from selected single plants of each line as well as the overall percentage of sterility from each plot were recorded. The results from the growth chamber study revealed that 801s and 811s expressed sterility at a daytime temperature >29.4 °C and nighttime temperature >26.7 °C, while 236s expressed sterility when daytime temperature >32.2 °C and nighttime temperature >29.4 °C. The results also suggested that the different day lengths did not affect sterility in these lines. The field study showed that 811s expressed sterility in all three planting dates indicating that the optimum planting was May 10th. The 236s plants tested from the 1st planting date expressed sterility indicating that the absolute planting date was April 25. All GSOR lines in the growth chamber conditions remained fertile, however, in the field test a few plants of GSOR 2, GSOR 3, and GSOR 4 showed sterility. All GSOR 1 plants were fertile in the field condition. [ABSTRACT FROM AUTHOR]

The Arkansas rice breeding program has the ongoing goal to develop new long- and medium-grain cultivars as well as specialty cultivars including aromatics and Japanese quality short-grains. Cultivars are evaluated and selected for desirable characteristics. Those with desirable qualities which require further improvement are utilized as parents in future crosses. Important components of this program include: high-yield potential, excellent milling yields, pest and disease resistance, improved plant type (i.e. short stature, semidwarf, shorter maturity, erect leaves), and superior grain quality (i.e. low chalk, cooking, processing and eating). New cultivars are continually being released to rice producers for the traditional Southern U.S. markets as well as for the emerging specialty markets, which are gaining in popularity with rice consumers. This report describes the progress of the long-grain and specialty rice pure line rice breeding effort at the University of Arkansas System Division of Agriculture. [ABSTRACT FROM AUTHOR]

Researchers in molecular genetics at the University Of Arkansas System Division Of Agriculture's Rice Research and Extension Center (RREC) near Stuttgart, Ark. have been performing DNA marker-assisted selection (MAS) for over 17 years. Currently four rice breeding programs and cooperative extension activities utilize the laboratory. Much of the effort over the last 17 years has been devoted to the genotypic characterization of parental lines and progeny in the areas of new long-grain and medium-grain cultivar development, hybrid rice breeding, aromatic rice breeding, backcross populations, genomic mapping of specific traits, and seed purification. In 2017, genetic analysis was performed on 10 major projects for breeding involving DNA marker-assisted selection for the important traits of cooking quality, rice blast disease resistance, and Clearfield resistance. Eight other smaller projects were conducted for the breeding programs and two small projects for Rice Extension Agronomy. The Molecular Genetics lab focused considerable effort towards the hybrid rice breeding program, screening 4123 samples with up to 28 markers. The hybrid rice projects included parental materials, male-sterile and restorer lines, and selected F1 hybrid lines in development currently. In total, the lab processed 5656 mostly bulked genomic DNA samples, generating 54,571 data points for the year. The work was accomplished using 65 DNA template plates, 621 PCR plates, 172 runs on the ABI 3500xL, and 77 KASP runs. [ABSTRACT FROM AUTHOR]

In 2010, the University of Arkansas System Division of Agriculture, established the rice hybrid program to develop very high yield rice hybrids with good seed quality for the mid-Southern United States. In 2017 potential environment sensitive male-sterile lines (EGMS) possessing genes associated with good cooking quality for the "Two-line hybrid rice system" were developed. We continued developing several restorer lines (R line) for the "Three-line hybrid rice system". Hybrid (F1) seeds were produced from crosses between the U of A male-sterile lines and Arkansas elite cultivars. Experimental hybrid lines developed during the summer of 2016 were evaluated for yield and quality characteristics. Combinating ability of experimental male-sterile lines was evaluated in a heterosis study. New sources of Environmental genic male-sterile lines were introduced from the International Rice Research Institute (IRRI) in the Philippines. Several advanced lines from the long and medium grain programs were selected to be used in hybrid rice development. Extensive phenotypic and molecular evaluations were completed to improve disease resistance and cooking quality, and to identify semi dwarf, non-aromatic plants. [ABSTRACT FROM AUTHOR]

To reflect the recent changes of the state rice industry and streamline the delivery of new and improved rice varieties to the Arkansas rice growers, the new medium-grain rice breeding project will expand its research areas and breeding populations to include both conventional and Clearfield medium- and semidwarf long-grain rice, as well as hybrid rice. Newest elite breeding lines/varieties from collaborating programs, as well as lines with diverse genetic origins will be actively collected, evaluated, and incorporated into the current crossing blocks for the programmed hybridization. To improve the efficiency and effectiveness, maximum mechanized-operation, multiple generations of winter nursery, and new technologies such as molecular marker-assisted selection (MAS) will also be rigorously pursued. [ABSTRACT FROM AUTHOR]

The University of Arkansas System Division of Agriculture's, Rice Research and Extension Center (RREC) Hybrid Rice Breeding program has two separate activities: developing hybrid rice and hybrid rice parental lines. The hybrid breeding activities for hybrid rice production include hybrid seed (F1) production, preliminary study and Arkansas Rice Performance Trials (ARPT), and developing restorer and male-sterile lines. Efforts for developing hybrid parental lines include a winter nursery for advance generation of different populations, developing male-sterile and restorer lines designated as female and male parents, respectively. The main focus in 2019 was to develop experimental hybrid lines and to evaluate them through preliminary and ARPT tests. These efforts continue in 2020. [ABSTRACT FROM AUTHOR]