Elite Rice Lines Research Articles

Evaluation of elite rice lines for resistance to Kenya blast fungus (Magnapothe Oryzae)

Blast resistance tends to often break down, these necessitate search-resistant genes. The screen house experiment was conducted in 2019 and 2020. A total of 56 rice genotypes, (Elite lines, monogenic lines, and local), were screened against ten Kenya isolates of Mangnaporthe oryzae. The establishment was by direct seeding of previously sprouted seeds. A completely Randomized Design (CRD) with two replicates was adopted. Inoculation was done 21 days after planting. Plants were maintained in the moist chamber (26–28 0C) for 48 hrs, then moved into an incubation chamber (25 ◦C ± 2). Disease assessment commenced 48 hours after inoculation until 21 days to full infection. Disease evaluations were performed according to the Standard Evaluation System of IRRI. Polymerase Chain Reactions (PCR) were carried out, blast resistant loci were identified using varied genetic markers that co-segregate with specific resistant loci Analysis was implemented in R version 3.3.2 (R Core Team, 2016). BLUPs were computed, in a mixed model to estimate the random effect of the genotypes. The data was subjected to analysis of variance and means separated by Tukey’s test at P < 0.05. Cluster analyses were performed in JMP software version 11.2 for Windows. Seven genotypes (IR12A311, IR10M210, IR74, 1R02A127, IR09A130, R66 and IR10N230) were more susceptible, IR13N152 and IR14F711 were more resistant to all Isolates. The monogenic lines IRBLsh-B and IRBLkh-K3 which carry blast-resistant genes, were susceptible to at least seven Kenya isolates. The local checks (Basmati 370, BAS 270 (pi9), BW196, and BAS370 (pi9) were highly susceptible. The genotype IR12F711 was consistently resistant to all Kenya Isolates.

Drought stress in rice: morpho-physiological and molecular responses and marker-assisted breeding.

Rice (Oryza Sativa L.) is an essential constituent of the global food chain. Drought stress significantly diminished its productivity and threatened global food security. This review concisely discussed how drought stress negatively influenced the rice's optimal growth cycle and altered its morpho-physiological, biochemical, and molecular responses. To withstand adverse drought conditions, plants activate their inherent drought resistance mechanism (escape, avoidance, tolerance, and recovery). Drought acclimation response is characterized by many notable responses, including redox homeostasis, osmotic modifications, balanced water relations, and restored metabolic activity. Drought tolerance is a complicated phenomenon, and conventional breeding strategies have only shown limited success. The application of molecular markers is a pragmatic technique to accelerate the ongoing breeding process, known as marker-assisted breeding. This review study compiled information about quantitative trait loci (QTLs) and genes associated with agronomic yield-related traits (grain size, grain yield, harvest index, etc.) under drought stress. It emphasized the significance of modern breeding techniques and marker-assisted selection (MAS) tools for introgressing the known QTLs/genes into elite rice lines to develop drought-tolerant rice varieties. Hence, this study will provide a solid foundation for understanding the complex phenomenon of drought stress and its utilization in future crop development programs. Though modern genetic markers are expensive, future crop development programs combined with conventional and MAS tools will help the breeders produce high-yielding and drought-tolerant rice varieties.

Pathogenicity and Genetic Variations in Magnaporthe oryzae Isolates from One Rice Variety Planting in Paddy and Upland Fields

Rice is the most important crop for worldwide consumers. The water utilization of rice planting is more than 50% of agricultural water in China, and it is necessary to breed water-saving and drought-resistant rice. The rice variety Dianheyou 615 can be planted in the paddy and upland fields, which satisfies rice production farmers in mountainous regions of Yunnan. We aimed to explore the variations in Magnaporthe oryzae isolates collected from Dianheyou 615 planted in paddy or upland fields. Through pathogenicity tests, we found that most isolates had the highest pathogenicities, but there were no significant differences between the paddy and upland isolates. By a combination of monogenetic and elite rice lines, with a further resistance assessment, the monogenetic lines with Pi9, Diantun 506, and Lvhan 1 displayed better resistances. Moreover, we re-sequenced 15 isolates to explore their genetic variations. Our results showed that the source of the upland isolates may have been the offspring of the paddy isolates, but there were many genes with specifically found SNPs in two populations that would develop subdivisions after long-time planting. Overall, we compared the pathogenicities and genetic variations in blast isolates from the planting of Dianheyou 615 in paddy and upland fields, which provided references for the influence of the planting environment on population subdivisions.

Molecular and morpho-agronomic traits for vegetative stage drought tolerance in some rainfed elite rice lines

Selection of drought-tolerant rice genotypes is still one of the most vital challenges in rice research and the use of molecular markers may offer a promising approach to fast track the selection and development of drought-tolerant rice. The aim of our study is to identify drought-tolerant traits, in selected rainfed elite rice lines, expressed during drought stress at the vegetative stages 20-32 DAS and 30-42 DAS. The study also validated the presence of SSR markers linked to drought tolerance. All morpho-agronomic traits examined in the study were significantly affected by drought, except for root length during 30-42 DAS of drought imposition. Drought significantly reduced the plant height, number of tillers, leaf area, and root number resulting in a significant reduction in root and shoot dry weight. On the other hand, an increase in total nodal root length was observed in all test genotypes except for AL-55, AL-97, and susceptible check PSB Rc82 under both drought conditions. All parameters examined in this study are useful traits for drought tolerance in rice, however responses might be genotype-dependent. The highest correlation was shown by root:shoot ratio (r=0.94, r=0.78) at 20 DAS and (r=0.89, r=0.67) at 30 DAS under well-watered and drought conditions, respectively. Seven amplified markers were present in the test genotypes except for RM 525, RM 60, RM 201, RM 1141. These four markers were absent in the drought-susceptible check PSB Rc82, hence, these markers may be used in selecting drought-tolerant genotypes through marker-assisted selection.

Unravelling genetic architecture and development of core set from elite rice lines using yield-related candidate gene markers.

The online version contains supplementary material available at 10.1007/s12298-022-01190-8.

Performance of Doubled Haploid Elite Rice (Oryza sativa L.) Germplasm for Grain Yield and Associated Traits in Harare, Zimbabwe

A field experiment was conducted in 2018/2019 growing season at the Scientific Industrial Research and Development Center under irrigated conditions using the simple alpha lattice (7 ∗ 7) design, with three replications. The objective of the study was to determine the performance of 44 elite rice lines that were selected and shared from elite doubled haploid germplasm and five cultivars were used as checks. All evaluated genotypes exhibited significant variation in the traits measured except for number of grains/panicle, total tillers/plant, and effective tillers/plant. Elite line 70462 was found to be the highest yielding, with yield advantage of 66% over the high yielding local check (Nerica 7). High values for broad sense heritability were recorded for days to 50% heading, panicle length, culm length, number of filled grains/panicle, 1000-grain weight, grain length, grain shape, and grain yield and indicated lesser influence of environment in expression of these traits, hence amenable to simple selection. Correlation analysis revealed that grain yield manifested significantly positive correlation with filled grains/panicle contributing the highest correlation (r = 0.784), followed by culm length (r = 0.605), spikelet fertility/panicle (r = 0.677), grain length (r = 0.551), 1000-grain weight (r = 0.518), panicle length (r = 0.449), and number of grains/panicle (r = 0.328). Based on grain yield, number of filled grains/panicle and spikelet fertility/panicle, panicle length, and earliness, lines 70462, 60143, 70383, Arica 3, Sahel 177, 6040, 70537, 60409, and 70476 had the best performance. Selection of these traits would be more effective for yield improvement in rice and these promising lines could be used in the varietal development and can be tested in multilocational trials and on-farm trials in Zimbabwe with the possibility of release and commercialization.

Genetic Diversity Analysis and Molecular Characterization of Elite Rice Promising Lines for Yield, Blast Disease Resistance and Rice Stem Borer تحليل التنوع الوراثى والتوصيف الجزيئي لمحصول سلالات الارز المبشرة، ومقاومتها لمرض اللفحة وثاقبة ساق الارز

Developing and cultivating new promising rice lines with high yield potential and blast disease resistance is an important goal of rice breeding. The study was to evaluate some developed new elite rice lines for high yield, blast resistance, effective resistance genes to Pyricularia grisea and rice stem borer insect as well as assessment of the genetic diversity in these lines using microsatellite markers. Significant differences were found among the studied new promising lines and their parents for yield and its component traits. Promising lines; GZ11190-3-13-1-1 and GZ11190-3-13-4-1 gave the highest grain yield compared with their parents; Giza 178 and GZ6296-12-1-2-1-1 and superiority for all studied traits. Also under this study, twenty six isolates were identified as five main groups i.e., IC, ID, IF, IG and IH, but ID and IH groups were considered the most common race, Pib resistance gene was the most effective gene to blast fungus. Promising lines GZ11190-3-13-1-1 and GZ11190-3-13-4-1 proved resistance for all tested isolates under greenhouse condition and moderately resistant for stem borer insect. For genetic diversity analysis, twenty SSR markers were polymorphic amplifying a total of 102 alleles. Characterization of these markers showed high discriminating power with an average polymorphism information content (PIC) of 0.754.Major allele frequency ranged from 0.475 (RM590) to 0.923 (RM5 and RM5313), with an average of 0.705. The cluster analysis based on microsatellite SSR markers grouped 13 rice genotypes into clear separate groups and was able to reveal close genetic relationships between rice genotypes used in rice breeding program.

Fe and Zn content of various genetic background of released rice varieties in Indonesia

Fe and Zinc deficiency is one of the most prevalence micro nutrient disorder in Indonesia. Increasing of Fe and Zn content in rice grain is expected to be useful to reduce the micronutrient deficiency. This research was aimed to identify rice varieties containing high Fe and Zn content and initially study the correlation among some related traits. The experiment was conducted in October – December 2016 by testing 176 released varieties and 4 elite rice lines. The samples were prepared as brown rice. Fe and Zn contents were measured using XRF Oxford machine which is validated by ICP method. The results showed that Fe content of the tested genotypes is normally distributed ranged from 9.70 ppm to 17.40 ppm with the mean of 13.03 ppm and the Zn content is not normally distributed ranged from 15.80 ppm to 31.10 ppm with the mean of 22.41 ppm. Majority of the released rice varieties in Indonesia had lower Fe and Zn content compared to the most popular variety, Ciherang (12.20 ppm and 24.70 ppm). Kalimutu had the highest both for Fe and Zn content (17.40 ppm and 31,10 ppm). Fe and Zn content are positively correlated and breeding effort for both traits is prospective.

Development of rice introgression lines with brown planthopper resistance and low amylose content for germplasm sources through marker-assisted selection

The brown planthopper (BPH) is one of the most serious problems affecting rice production. This study incorporated the BPH resistance gene, Bph3, derived from a Rathu Heenati × Pathumthani 1 variety, which is susceptible to BHP and has low amylose content in the endosperm and both of these traits are closely linked on chromosome 6. The objective of this study was to develop introgression lines as germplasm sources with BPH resistance and low amylose content with other removed linkage drag traits and photoperiod insensitivity using marker-assisted selection. The newly developed multiplex simple sequence repeat markers specific to both genes were utilized for screening of the F2 progeny possessing genotypes with breaking linkage drag and selected photoperiod insensitive lines. Then, evaluation of the selected lines for BPH resistance was conducted in the seedling stage of the F4 progeny and the resistant character was segregated. Selection was made for BPH-resistant plants and their genotype controlling resistance on chromosome 4 was additionally determined using marker RM 16355. The results revealed that all the selected plants had the same genotype as the Rathu Heenati variety. Finally, the elite rice lines could be used as a germplasm source in rice breeding for BPH resistance and low amylose content. Moreover, unfavorable traits were removed by phenotypic selection from the Rathu Heenati variety such as photoperiod sensitivity, non-fragrance and tall plant type. Thus, these rice lines can be used as a germplasm resource for a rice breeding program in the future.

Identification of QTLs for Blast, Bacterial Blight, and Planthopper Resistance Using SNP-Based Linkage Maps from Two Recombinant Inbred Rice Lines

Rice is the most significant global food security. Several biotic factors limit rice production, breeding biotic-resistant rice has, therefore, become an increasingly important goal. Two elite rice lines, IR71033-121-15 (IR71033) and IR57514-PMI-5-B-1-2 (IR57514), provide potential genes for biotic stress resistance traits. In this study, genotyping by sequencing (GBS) for single nucleotide polymorphism (SNP)-based linkage map construction was used to detect quantitative trait loci (QTLs) for blast (BL), bacterial blight (BB), whitebacked planthopper (WBPH), and brown planthopper (BPH) resistance. IR71033 was derived from Oryza minuta and carried BL, BB, WBPH, and BPH resistance QTLs. IR57514 is a well-adapted rainfed lowland line that carries BL and BB resistance QTLs. Two sets of recombinant inbred line (RIL) populations derived from crosses of KDML105 × IR71033 and KDML105 × IR57514 were used to dissect the genetic basis of disease and insect pest resistance. The RIL populations were evaluated for BL, BB, WBPH, and BPH resistance from 2016 to 2018 at four rice research centers in Thailand. From these, we identified a large number of SNPs through GBS and constructed high-resolution linkage maps. By combining phenotypic evaluation with the GBS data, a total of 24 QTLs on four chromosomes were detected that confered pest resistance and explained 7.3% - 61.4% of the phenotypic variance. These findings should facilitate identifying novel resistance genes and applying marker-assisted selection for resistance to the four major rice pests investigated here. These strategies will improve the resilience and reliability of rice varieties adapted to the low-yielding environment of rainfed lowland areas worldwide.

Developing Blast Disease Resistance of Jasmine Rice by Phenotypic-Genotypic Simultaneous Selection

Breeding for resistant varieties of rice is known to be the most preferable way of controlling blast disease (Pyricularia oryzae). Identification and introduction of resistance genes into elite rice lines has become possible by the use of molecular markers. KD2-1 line is an isogenic line of KDML105 carrying four resistance genes on chromosome 2, 3, 8 and 12 from IR64 variety. The objective of this research was to transfer blast disease resistant genes from KD2-1 line into RD15 variety by using phenotypic and genotypic selections by the aid of markers. In this study, the four resistance genes were transferred from KD2-1 rice line into a blast susceptible rice variety, RD15. The study resulted in the breeding of four elite rice lines with four resistance genes by phenotypic and foreground selection. The genome-wide SSR marker analysis of the lines showed more than 86.5% background genome recovery of RD15. Pathogenicity assays of the four selected lines exhibited a resistant reaction to all 13 isolates, with agronomic and yield performance, and cooking and eating quality characteristics similar to that of RD15. The phenotypic-genotypic (foreground and background) simultaneous selection strategy is very useful to introduce multiple resistance genes in rice as it is a fast and economical way for identification of anticipated recombinant lines with desired genes.

Variation in Expression of <i>Sub</i>1 Gene and Association with Submergence Stress Related Traits in Advance Rice (<i>Oryza sativa</i> L.) Genotypes as a Tool of Climate Change Adaptation

Floods have now become most detrimental natural catastrophe worldwide due to radical climatic fluxes. Therefore, there is a dire necessity to develop a high yielding rice lines to deal with this scenario. For this purpose, a large scale experiment was conducted including one hundred and fifteen (115) rice genotypes having SUB1 gene imported from International Rice Research Institute (IRRI) Philippines, six local cultivars/approved varieties and three high yielding rice varieties i.e. Sabitri, IR6 and NSICRC222 being used as potential varieties in different countries of Asia as susceptible check and IR64-SUB1 as tolerant check. The genotypic screening was performed using two PCR-based DNA markers i.e. ART5 and SC3. Phenotypic screening was conducted in a natural pond to assess the interaction of SUB1 gene in natural stagnant flood water as well as the suitability of introgression of SUB1 gene into approved varieties and elite rice lines. The genotypes were assessed in terms of plant survival percentage, submergence tolerance index, physical condition, stem elongation, number of grains per panicle, thousand grain weight, grain yields and deviations in these traits after submergence stress. The PCR results suggested that both the primers ART5 and SC3 may be used as potential PCR-based markers for molecular screening of rice genotypes for SUB1 QTL. Furthermore, it confirmed the presence of SUB1 gene in all the lines imported from IRRI, while it was absent in all the local cultivars studied. All the genotypes with submergence tolerant gene (SUB1) showed significantly greater tolerance level in submergence stress of 14 days, as compared to other local cultivars/varieties, authenticating the effectiveness of SUB1QTL in conferring submergence tolerance. Significantly different performances of all the SUB1 genotypes in terms of all the studied traits indicate high Genotypic and Genotypic Environment Interaction (GEI) of SUB1QTL. Employment of SUB1 lines such as R105479:149-18, IR64-SUB1 and Rl05469:81-22-3 in breeding programs for developing flood tolerant rice varieties might further upsurge rice yields in flash flood areas. Correlation analysis revealed that plant survival percentage after submergence, reduced stem elongation during submergence and submergence tolerance index are very important traits for developing submergence tolerant lines.

Characterization of Submerged Tolerant Elite Rice Genotypes Having Improved Physiological Traits and Oxidative Defense System grown under Rainfed Lowland Ecosystem of Eastern Indo-Gangetic Plains

An experiment was conducted in 2014 and 2015 kharif season to evaluate the performance of rice genotypes under submerged condition on the basis of morpho-physiological traits and yield attributes. The study revealed that rice var. Swarna Sub 1 exhibited the highest survival (91.2%), whereas var. IR42 as susceptible check showed the least survival (4.2%) under submergence. Among the tested genotypes, IR 10F365, IR 11F216 and IR 11F239 with the respective survival values of 81.4, 80.0 and 78.1%, respectively, were found to be at par with the var. Swarna Sub 1 after 16 days of complete submergence at vegetative stage. Moreover, physiological traits like chlorophyll, sugar content and anti-oxidative system (SOD and CAT) were higher in tolerant genotypes as compared to susceptible ones. Less reduction in the content of sugar, chlorophyll, SOD and CAT activity was observed in genotypes IR 10F365, IR 11F216 and IR 11F239 along with var. Swarna Sub 1 (tolerant check) after submergence, while in susceptible genotypes IR 09L311, IR 08L216 and IR 55423-01 the reduction in sugar and chlorophyll content was higher just after submergence. Apart from physiological traits, tolerance genotypes have higher yield and yield attributing character as compared to susceptible genotypes. Thus, the study revealed that not only var. Swarna Sub 1 even few more elite rice lines found superior in terms of submergence tolerance and yield.

Gene action of elite rice lines for yield and lodging resistance related traits

Knowledge of gene action on yield and lodging related traits would help in framing suitable breeding strategy for the development of lodging resistance genotypes with high yield. Present investigation aimed at studying gene action among the eight yield and six lodging resistance related traits in two crosses MTU 7029/II 110-9-1-1-1-1 and MTU 7029/MTU 1121 using six-parameter model of generation mean analysis. The results revealed significance of scaling test for all the traits indicating inadequacy of additive dominance model for explanation of inheritance of 14 traits in both the crosses except for number of ear bearing tillers/plant, test weight and grain yield/plant in case of MTU 7029/MTU 1121. In both the crosses, characters number of filled grains/panicle, spikelet fertility, test weight, culm diameter and panicle length expressed complementary epistasis besides dominance x dominance interaction. Hence, biparental mating followed in early generations and selection could be practised in advanced generations to fix favourable alleles. Rest of the traits such as number of ear bearing tillers/plant, grain yield/plant, culm thickness, culm strength, basal internodal length and per cent of lodging exhibited duplicate type of epistasis. Characters with non-additive gene action coupled with duplicate type of gene interaction can be improved by recurrent selection or diallel selective mating.

Recent Updates on Salinity Stress in Rice: From Physiological to Molecular Responses

One-fifth of irrigated agriculture is negatively affected by high soil salinity. The expected population growth, over 9 billion by 2050, enhances the pressure for agricultural production in marginal saline lands. Rice (Oryza sativa L.), the staple food for more than half of the world's population, is the most salt-sensitive cereal. The need for salt-tolerant rice varieties able to cope with several other stress conditions obviously puts a lot of pressure on breeders who must better comprehend the physiology and genetic control of salt tolerance. In spite of several good reviews recently published, an integrated vision of current information on rice tolerance to salt stress has been lacking. Here we present the most recent data on the salinity effect on rice physiology and stress adaptation, including implications on growth regulation and reproductive development. We have included an inventory of salt tolerance donors available for breeding programs and a comprehensive survey of current work on QTL detection and cloning as well as marker-assisted selection to introgress favorable alleles into elite rice lines. A schematic view of the rice chromosomes on which salt tolerance QTLs and candidate genes are positioned is also included. Finally, we focus on the most promising candidate genes involved in salt stress response. There, we discuss the available knowledge on salt stress signaling and ion homeostasis, LEAs and other stress-induced proteins, genes with unknown function and transcription regulators as well as the present knowledge on the role of post-translational modifications on the modulation of the response to salinity in rice. We conclude by highlighting still missing clues that could help to design better salt tolerant varieties, and we evaluate the significance of the data presented for the future of rice breeding and sustainability of the culture in marginal saline soils.

Hidden diversity for abiotic and biotic stress tolerances in the primary gene pool of rice revealed by a large backcross breeding program

Low and unstable rice productivity in many areas of Asia is associated with many abiotic and biotic stresses such as drought, salinity, anaerobic conditions during germination, submergence, phosphorus and zinc deficiency, etc. To develop rice varieties with tolerance to these stresses, we undertook a large backcross (BC) breeding effort for the last 6 years, using three recurrent elite rice lines and 203 diverse donors, which represent a significant portion of the genetic diversity in the primary gene pool of rice. Significant progress has been made in the BC breeding program, which resulted in development of large numbers of introgression lines with improved tolerance to these stresses. Promising lines have been developed with excellent tolerances (extreme phenotypes) to salinity, submergence and zinc deficiency; resistance to brown plant hopper, ability to germinate under the anaerobic condition and low temperature. Our results indicated that there exist tremendous amounts of ‘hidden’ diversity for abiotic and biotic stress tolerances in the primary gene pool of rice. Furthermore, we demonstrated that despite the complex genetics and diverse physiological mechanisms underlying the abiotic stress tolerances, introgression of genes from a diverse source of donors into elite genetic backgrounds through BC breeding and efficient selection (careful screening under severe stress) is a powerful way to exploit this hidden diversity for improving abiotic stress tolerances of rice. We have developed three large sets of introgression lines, which not only provide an unique platform of breeding materials for developing new rice cultivars with superior yield and stability by trait/gene pyramiding, but also represent unique genetic stocks for a large-scale discovery of genes/alleles underlying the abiotic and biotic stress tolerances of rice using genomic tools.

Development of PCR-based markers for thermosensitive genetic male sterility gene tms3(t) in rice (Oryza sativa L.).

Development of simple and reliable PCR-based markers is an important component of marker-aided selection (MAS) activities for agronomically important genes in rice breeding. In order to develop PCR-based markers for a rice thermosensitive genetic male sterility gene tms3(t), located on chromosome 6, the nucleotide sequences of four linked RAPD markers OPF18(2600), OPAC3(640), OPB19(750) and OPM7(550) were used to design and synthesize several pairs of specific primers for PCR amplification of the genomic DNA of both the parents IR32364TGMS (sterile) and IR68 (fertile), involved in mapping this gene. For the RAPD marker OPF 18(2600), two pairs of specific primer pair combination from different positions of the sequence resulted in generation of two codominant STS (Sequence Tagged Sites) markers. In case of markers OPAC3(640), OPB19(750) and OPAA7(550) the first two could generate dominant polymorphism, while the last one could not be successful in PCR amplification. Both the codominant STSs with primer combinations F18F/F18RM and F18FM/F18RM were found to be tightly linked to the tms3(t) gene with a genetic distance of 2.7 cM. The sizes of the different alleles in case of F18F/F18RM, F18FM/F18RM combinations were 2300 bp, 1050 bp, and 1900 bp, 1000 bp respectively. The efficiency of marker-assisted selection for this trait was estimated as 84.6%. Polymorphism survey of 12 elite rice lines, indicated that these PCR-based markers for tms3(t) can now be used in selecting TGMS plants at seeding stage in the segregating populations in environment independent of controlled temperature regime.

Pyramiding transgenes for multiple resistance in rice against bacterial blight, yellow stem borer and sheath blight.

Here we describe the development of transgene-pyramided stable elite rice lines resistant to disease and insect pests by conventional crossing of two transgenic parental lines transformed independently with different genes. The Xa21 gene (resistance to bacterial blight), the Bt fusion gene (for insect resistance) and the chitinase gene (for tolerance of sheath blight) were combined in a single rice line by reciprocal crossing of two transgenic homozygous IR72 lines. F4 plant lines carrying all the genes of interest stably were identified using molecular methods. The identified lines, when exposed to infection caused by Xanthomonas oryzae pv oryzae, showed resistance to bacterial blight. Neonate larval mortality rates of yellow stem borer ( Scirpophaga incertulas) in an insect bioassay of the same identified lines were 100%. The identified line pyramided with different genes to protect against yield loss showed high tolerance of sheath blight disease caused by Rhizoctonia solani.

Identification of quantitative trait loci and epistatic interactions for plant height and heading date in rice.

Appropriate heading date and plant height are prerequisites for attaining the desired yield level in rice breeding programs. In this study, we analyzed the genetic bases of heading date and plant height at both single- locus and two-locus levels, using a population of 240 F(2:3) families derived from a cross between two elite rice lines. Measurements for the traits were obtained over 2 years in replicated field trials. A linkage map was constructed with 151 polymorphic marker loci, based on which interval mapping was performed using Mapmaker/QTL. The analyses detected six QTLs for plant height and six QTLs for heading date; collectively the QTLs for heading date accounted for a much greater amount of phenotypic variation than did the QTLs for plant height. Two-way analyses of variance, with all possible two-locus combinations, detected large numbers (from 101 to 257) of significant digenic interactions in the 2 years for both traits involving markers distributed in the entire genome; 22 and 39 were simultaneously detected in both years for plant height and heading date, respectively. Each of the interactions individually accounted for only a very small portion of the phenotypic variation. The majority of the significant interactions involved marker loci that did not detect significant effects by single-locus analyses, and many of the QTLs detected by single-locus analyses were involved in epistatic interactions. The results clearly demonstrated the importance of epistatic interactions in the genetic bases of heading date and plant height.

Field performance of transgenic elite commercial hybrid rice expressing Bacillus thuringiensis δ-endotoxin

Here we describe development of transgenic elite rice lines expressing a Bt fusion gene derived from cryIA(b) and cryIA(c) under the control of rice actinI promoter. The lines used in the study were indica CMS restorer line of Minghui 63 and its derived hybrid rice Shanyou 63. The level of Bt fusion protein CryIA(b)/CryIA(c) detected in Minghui 63 (T51-1) plants was 20 ng/mg soluble protein. The Bt Shanyou 63 was field-tested in natural and repeated heavy manual infestation of two lepidopteran insects, leaffolder and yellow stem borer. The transgenic hybrid plants showed high protection against both insect pests without reduced yield.