Rice Improvement Programs Research Articles

Transgressive segregation and generation mean analysis reveal the gene action underlying the inheritance of drought tolerance in rice

Climate change, an effective driver of unprecedented seasonal droughts, is greatly affecting rice production in Africa by threatening food security and safety. Rice, one of the major staple crops on the continent, can save the situation through the development of drought-tolerant cultivars, presenting a major challenge for future rice improvement programs as drought is regarded as a critical limitation in rain-fed ecosystems. This study sought to understand the genetic basis and inheritance behind the expression of tolerance of rice breeding lines to drought-stress through generation mean analysis. To achieve these objectives, two drought-sensitive genotypes (Jasmine 85 and CRI-Agrarice) were crossed with a drought-tolerant genotype (APO) to develop six populations (F1, F2, BC1, BC2, P1 and P2) under screenhouse drought-stress and non-stress evaluation. Data were collected on grain yield and yield-related traits among which the generation mean analysis was conducted. At least one transgressive phenotype was produced in the F2 population for each trait whether there is a significant difference or not among the parental lines under drought-stress. Under non-stress conditions, there was a significance for all six types of gene action for days to flowering in both crosses. Among both crosses and water-regimes, additive x additive gene interaction was significant for most of the traits even though the scaling tests were not significant indicating the effectiveness of selection in early generations. Therefore, either forward breeding or backcross breeding can be adopted as breeding strategies for rapid improvement for these lines to drought tolerance.

Path Coefficient Analysis and Character Association of Yield and Yield Contributing Traits of Rice Landraces

An experiment was carried out during Kharif 2020 to estimate the direct and indirect effects of various independent characteristics on the dependent character and to assess the degree of relationship between yield and yield contributing traits of rice landraces. The experimental material consists of 188 landraces including two checks IR-64 and Jeerashankar and these genotypes were planted in Randomized Block Design with three replications. Based on correlation and path analysis studies, significant positive correlation and high direct positive effect on grain yield per plant were found for traits flag leaf length, number of tillers, number of effective tillers, panicle weight, harvesting index, panicle index, fertile spikelet per panicle and biological yield per plant. Itdepicted that during the formulation of criterion in the rice improvement program as well as for plant ideotype, these traits would be of significant relevance.

SCREENING OF RICE VARIETIES TOLERANT AND SUSCEPTIBLE TO IRON TOXICITY IN INLAND VALLEY SWAMPS (IVS) IN SIERRA LEONE

Iron toxicity is a nutrient disorder, which is brought about by the uptake of Fe (II) in amounts that disrupt or over-expressseveral metabolic processes, resulting in damage to the rice plant. A pot experiment was conducted in a greenhouse at Sierra Leone Agricultural Business Initiatives (SABI) Center Newton to enable the screening of many different varieties thereby resulting in the identification of both tolerant and susceptible varieties that could be used as breeding materials for rice improvement programs in the tropics. The hot spot iron toxic soils used in the pot were weighed at a uniform rate The parameters or items of measurement to be looked at could be the dry weight of root, dry weight of stem, dry weight of filled grain, dry weight of unfilled grains, plant height (cm) of the genotypes, tiller number of the genotypes, leaf area (cm2)of the genotypes, phenotypic acceptability of the genotypes, Iron-toxicity score of the genotypes Based on their performance in terms of toxicity scores, dry root weight, stem weight, leaf area, unfilled grains, filled grains, tiller count, plant height, and phenotypic acceptability the following varieties have been identified as iron toxicity tolerant with high yield potential Gbassay, Rok-24, Chim, kiamp.

Evaluation of Yield Indices and Identification of Yield Responsive Genes (Gn1a and Gs3) of Selected Rice Genotypes

This research aimed at evaluation of yield Indices and identification of yield responsive Genes (Gn1a and Gs3) of selected rice Genotypes. A total of ten rice genotypes including four improved rice (high yielding) genotypes and six local rice (landraces) genotypes obtained from Maslaha seeds limited Gusau, Zamfara State were collected. The Data was collected for plant height, tiller number, number of panicles, panicle length, panicle weight and days to 50% flowering were recorded, grain length and seed dimension was measured. The genomic DNA of the Rice accession was extracted using a standard DNA extraction Kit (Plant/Seed Miniprep kit). The PCR reaction was set using a total of 40 ul reaction mixture containing 4ul 10x dream taq green buffer, 1.0 ul of dNTPs, 2.0 ul of each primer, 0.4ul of dream taq total nucleic acid polymerase, 2ul total nucleic acid template and 28.6 ul of molecular grade water. The Data collected for grain yield attribute and seed germination was subjected to one way analysis of variance (ANOVA) using statistical analysis system (SAS Version 9.4). The results were expressed as mean + Standard Deviation (SD) of three replicates and the differences between the means were separated using Duncan’s new multiple range test (DNMRT). The result showed that significant differences exist amongst entries for plant height at maturity. Panicle length observed in this study was significantly different in all the entries with FARO67 (25.92cm) recorded the highest compared to genotype Bvfort (20.37cm) which had the lowest. PCR products revealed the presence of Gn1a and Gs3 genes in the ten rice cultivars screened. Eight rice cultivars (FARO44, FARO59, FARO67, Bvfort, Fanjim, Kamrun, Maikwalli and Jamila) have Gn1a and Gs3 gene and shows during PCR Analysis while the remaining two cultivars (FARO60 and Danruwa) have the gene but do not show during the PCR analysis. This investigation therefore, recommends that accessions like Danruwa, kamrun and FARO60 which showed desirable yield, quantitative and qualitative traits in this study should be used for further rice improvement programmes.

Assessing Genetic Diversity and Population Structure of Rice Genotypes using ISSR Markers

Background: The realm of genetic diversity within rice is immense and undermining it provides the opportunity to utilize them in rice improvement programs. Hence in our study, we aimed to undermine the genetic composition and structure of the selected rice accessions utilizing ISSR marker systems. Methods: ISSR analysis encompassed a set of thirty genotypes, comprising 16 cultivated varieties and 14 landraces. The screening was performed with a total of 49 ISSR primers. The consensus tree constructed from banding patterns generated by ISSR-PCR clustered 30 genotypes according to their respective genomes. The Sequential Agglomerative Hierarchical Non-overlapping (SAHN) clustering was employed with the Unweighted Pair Group Method with Arithmetic Averages (UPGMA) method. The grouping of the 30 accessions was carried out through data analysis using NTSYSpc 2.02. Result: Utilizing 49 ISSR markers, the cluster analysis produced three clusters. These clusters displayed pronounced separation and exhibited evident patterns. The Cluster I encompassed Bharathi, BG367-2, PTB33, ASD9, ASD16, ASD20, Rathu Heenati and Columbia-2. Notably, the largest cluster was Cluster II comprising 20 accessions, while Cluster III contained only Jeeraga Samba and Basmati 370. The study validates the efficacy of ISSR markers in detecting polymorphism within and among rice populations and/or species. The resulting DNA profiles hold potential for serving as diagnostic fingerprints of both cultivated and wild rice germplasm, aiding in comprehending evolutionary relationships.

Nepalese Fine and Aromatic Rice Landraces: A Review

With the recent issue of Geographical Indication (GI) tag claim by India on Basmati rice, Nepalese rice sector got an urgent call to conserve and promote fine and aromatic rice landraces. Fine, medium, coarse landraces were further classified into aromatic and non-aromatic. Some of the aromatic landraces popularized by their local dialect names as Basmati anadi, Basmati anpjhutte, Choti basmati, etc. were cultivated in diverse environment by local farmers but utilization in national rice improvement program is insufficient. Just handful of landraces were used as parental lines to develop improved varieties viz. Jarneli in Khumal-2, Pokhreli masino in Khumal 4, Khumal -5 and Palung 2, pureline of Jethobudho as Pokhreli jethobudho, pureline of Lalkabasmati as Lalkabasmati. With the prevailing trend of fast-track registration of the exotic improved lines, our grassroots level efforts to study the genetic makeup and unique attributes of our landraces are overshadowed. However, Jarneli, Kalo marshi, Kalo nuniya, Mansara, etc. were found to be popular for traits nutritious, medicinal, abiotic stress tolerance and resilience to low fertility soil. Furthermore, the modern tools of molecular characterization are yet to be utilized prominently to identify such valuable genes and understand their phylogenetic diversity rewarding for future rice breeding program.

Estimation of genetic variability, correlation and path analysis in elite rice genotypes (Oryza sativa L.)

A trial was carried out to explore the variability and correlation among thirty five rice (Oryza sativa L.) germplasm for fifteen characters, during kharif 2017-18 at Bihar Agricultural University, Sabour, (Bihar). Analysis of variance revealed significant differences among all the genotypes and for all fifteen characters, which reflects that considerable amount of variability, were present in the genotypes. Two genotypes LPD104-B-B-1-8-2-1-1and RP5124-11-6-2 were identified as the superior genotypes for yield. The highest magnitude of genotypic coefficient of variation was recorded for length breadth ratio of rice grain, however highest phenotypic coefficients of variation were recorded for grain yield per plant followed by kernel length. High heritability coupled with high genetic advance as per cent mean was observed for kernel length and length breadth ratio. In this experiment grain yield per plant had positive and significant association with biological yield per plant, days to 50 per cent flowering, days to maturity, while remaining characters had non-significant association with yield. Path coefficient analysis revealed that the biological yield per plant, harvest index and kernel length had high positive direct effects on grain yield per plant indicating true relationship of these characters with grain yield. Therefore, these traits could be considered in rice improvement programme.

Performance of improved versions of Swarna introgressed with yield enhancing genes in multi-location trials

Swarna (MTU7029), an Indian mega-variety of rice, is cultivated on an estimated 8Mha of land. There is a pressing need to address yield stagnation and wider adaptability to irrigated lowland and rainfed ecologies as a result of the negative consequences of climate change and population growth. The present study was aimed at improving Swarna for two yield-related traits through marker-assisted backcross breeding strategy by introgression of OsSPL14 (panicle branching) and SCM2 (stronger culm). Foreground and background selection was carried out at each generation. Homozygous BC2F2 plants harbouring both yield-enhancing genes were identified and advanced through pedigree selection till BC2F5 and evaluated in station trials. Three promising lines possessing higher yield over recurrent parent were identified, and a single line, IET 27661 exhibited superior yield in multi-location trials of the All India Coordinated Rice Improvement Programme (AICRIP) and was found to be promising.

Genetic variation and population structure of Oryza sativa accessions in the AfricaRice collection and development of the AfricaRice O. sativa Core Collection

AbstractGenetic diversity studies provide an increased understanding of genebank collections and enhance their use for improving global food security. This study explores the genetic variation and population structure of 5738 rice (Oryza sativa L.) accessions representing 39.6% of the O. sativa collection conserved in the AfricaRice genebank of which 74.0% originated from African countries. These accessions were genotyped with 25,904 polymorphic DArTseq‐based single nucleotide polymorphisms (SNPs). Genetic distances between pairs of accessions indicate high variability, with 21.0% of pairs being moderately distant and 78.2% highly distant from each other. The genotyped accessions are traditionally grown in six different agro‐ecologies from 73 countries. Using neighbor‐joining tree, principal component, and model‐based population structure analyses, the accessions were divided into four genotypic groups representing the two O. sativa subspecies, Japonica (787 accessions) and Indica, which were further divided into landraces (1879 accessions), and improved cultivars (3027 accessions), and a fourth small group of admixed accessions. Subclusters identifying a specific agro‐ecology (upland, lowland, and mangrove swamp) or originating country were noted. Using the maximum length sub‐tree method, we selected 10% of the total accessions to form the “AfricaRice O. sativa Core Collection” (AROSCC). The subset of 600 O. sativa accessions captures more than 95% of the SNP polymorphisms in the entire collection. The AROSCC is an important resource to support pre‐breeding and rice improvement programs around the world.

Acclimatization of non-cultivated rice landraces to early moisture stress mediated by enzymatic antioxidants and osmolyte accumulation

Moisture stress affects the physiological and biochemical characteristics of plants such as the propensity for cellular water, induces stomatal closure, and reduces photosynthetic capacity, nitrate assimilation and substantial anabolic metabolism. In this study we assessed the antioxidative enzymes and osmolyte accumulation of fifty traditional non-cultivated rice landraces from Tamil Nadu, India. Artificial moisture stress was imposed in a hydroponic setup with maximum osmotic potential of (−) 15 bars. On the basis of drought and leaf rolling scores at 26 d, thirteen landraces were carried forward for further studies. The root/shoot ratio (R/S) was also significant for the selected landraces against IR64 as drought-susceptible check. The genotypes Kuliyadichan, Chandaikar, Mallikar, Nootripathu and Rajalakshmi were able to withstand intense moisture stress at 26 d with a score of 0 and 1, according to standard evaluation system for rice. Photosynthetic pigment and proline content of the above landraces increased during moisture stress in accordance with the positive check IR 64 (Drt1), however differential responses observed in all the landraces. Enzymatic antioxidant markers such as superoxide dismutase, catalase and peroxidase in shoots of all the selected landraces were greater than IR 64 (Drt1), under moisture stress. We identified Kuliyadichan, Rajalakshmi and Nootripathu as promising landraces with substantial moisture stress tolerance. Further, a positive correlation between overall seedling development and antioxidant enzymes as well as proline accumulation was observed under moisture stress. The mechanisms governing drought tolerance/avoidance in these moisture stress tolerant rice landraces might be attributed to active antioxidant defense system and proline accumulation for alleviating induced oxidative stress. Thus, the identified non-cultivated traditional rice landraces may be employed as potential donors for rice improvement programme towards climate resilience.

Utilization of Genetic Resources, Genetic Diversity and Genetic Variability for Selecting New Restorer Lines of Rice (Oryza sativa L.).

Exploration of and understanding diversity and variability in genotypes of germplasm determines the success of rice improvement programs. One of the most important determinants of the success of breeding programs is genetic diversity and inheritance of traits. Genetic variability analysis helps breeders to determine the appropriate selection method and standards to be used to improve the preferred trait. The aim of this study was to estimate genetic components, heritability and to obtain information about genetic diversity using cluster analysis and principal component analysis. Twenty rice genotypes with three replicates in a randomized complete block design were analyzed at the Experimental Farm at Sakha Agricultural Research Station, Sakha, Kafr El-Sheikh, Egypt, during the period from 2017 to 2020. The results of the analysis of variance showed that highly significant variations were recorded between the studied genotypes for all traits. The genotypic coefficient of variation (GCV%) and phenotypic (PCV%) coefficient of variation were moderate for plant height, panicles/plant, panicle weight, spikelets/panicle, filled grains/panicle, grain yield/plant and amylose content percentage for the first-year, second-year and combined data. This indicates the existence of beneficial genetic variability that can be exploited to improve these traits. The broad-sense estimates of heritability were high and recorded values higher than 60% for all the studied traits for the two-year and combined data, except for hulling percentage. This indicates that the selection of traits that have high heritability and are less affected by the environment leads to an acceleration of the improvement of these traits. The results from the cluster analysis and principal component analysis revealed a high level of genotypic variation among the studied genotypes and genetic diversity between them. One of the most important outcomes of this study is the successful utilization of genetic resources (germplasm) from ancient varieties and lines of rice in selecting and identifying 17 new restoration lines of rice, which have various improvement purposes in rice and hybrid rice breeding programs.

Genetic factors underlying anaerobic germination in rice: Genome-wide association study and transcriptomic analysis.

The success of rice (Oryza sativa L.) germination and survival under submerged conditions is mainly determined by the rapid growth of the coleoptile to reach the water surface. Previous reports have shown the presence of genetic variability within rice accessions in the levels of flooding tolerance during germination or anaerobic germination (AG). Although many studies have focused on the physiological mechanisms of oxygen stress, few studies have explored the breadth of natural variation in AG tolerance-related traits in rice. In this study, we evaluated the coleoptile lengths of a geographically diverse rice panel of 241 accessions, including global accessions along with elite breeding lines and released cultivars from the United States, under the normal and flooded conditions in laboratory and greenhouse environments. A genome-wide association study (GWAS) was performed using a 7K single-nucleotide polymorphism (SNP) array and the phenotypic data of normal coleoptile length, flooded coleoptile length, flooding tolerance index, and survival at 14 d after seeding (DAS). Out of the 30 significant GWAS quantitative trait loci (QTL) regions identified, 14 colocalized with previously identified candidate genes of AG tolerance, whereas 16 were potentially novel. Two rice accessions showing contrasting phenotypic responses to AG stress were selected for the transcriptomics study. The combined approach of GWAS and transcriptomics analysis identified 77 potential candidate genes related to AG tolerance. The findings of our study may assist rice improvement programs in developing rice cultivars with robust tolerance under flooding stress during germination and the early seedling stage.

A Study under Sodic Soil Condition for Estimation of Correlation and Path Coefficient Analysis of Rice (Oryza sativa L.) Yield and Its Component Traits

Effective selection necessitates knowledge of the nature and extent of population variation, character correlation with yield among individuals, and effect of environment on the assertion of these traits. Under timely seeded and irrigated conditions in sodic soil, this study used Augmented Block Design (ABD) to investigate correlations and path coefficients between yield and yield components in 85 germplasms, including four checks (Pusa sungandha-4, NDR-2065, sarjoo-52, Narendra usar-3). The correlation coefficient expresses the relationship between two variables, but it contains no information regarding cause and effect, such as which variable is dependent and which is independent. As a result, path-coefficient analysis must be utilized to examine the direct and indirect impact of numerous independent characters on a dependent character. The GYPP exhibited highly significant and positive correlations with BYPP and HI. When the genotypic correlation was assigned, it was discovered that characters like BYPP and HI had a positive direct impact on GYPP whereas characters DFF and DM were exhibited negative direct impact on GYPP. The most important indirect yield component was BYPP. As a result, these traits should be emphasized and further evaluated as a selection criterion for future rice improvement programmes in sodic soil.

Yield attributing traits of high zinc rice (Oryza sativa L.) genotypes with special reference to principal component analysis

Total 21 high zinc rice genotypes were evaluated under five different locations for 14 different yield attributing traits, including grain yield/plant (gm) to determine the pattern of variation, the relationship among the individuals and their characteristics through Principal Component Analysis (PCA) during the Kharif-2017. PCA was done for all the locations individually as well as pooled analysis for all locations using R software. Out of the 14 PCs, the initial four PCs contributed more to the total variability. The highest cumulative variability of the first four PCs found at Bhikaripur (81.11%) followed by BHU Agriculture research farm-II (79.23%) etc. and Pooled variability was 76.61%. Pooled data analysis indicates PCA biplot or loading plot of first two principal components revealed that days to maturity, days to 1st flowering date and days to 50% flowering loaded more on the first component and number of spikelets per panicles, number of grains/panicles, grain weight per panicle, grain yield/plant accounted more variation in the second component compared to the other parameters. Thus, the pooled analysis of principal component analysis revealed the characters contributing to the variation and genetic variability that exists in these rice genotypes. This is because the genotypes BRRIdhan 72, Sambamahsuri and Swarna were identified in different principle components related to grain yield and grain quality, and were also located farthest away from biplot origin in individual PCA based biplot. So they may be employed to improve yield attributing factors like total effective tiller number. PC1, PC2 and PC3 have days to first flowering and days to 50% flowering, hence their genotypes may be valuable in producing early maturing cultivars. Thus, the results revealed that wide range of variability was shown by different traits of the genotypes which can be utilized in rice improvement programmes.

Multiple-trait model through Bayesian inference applied to flood-irrigated rice (Oryza sativa L)

The objectives of this study were to use a bayesian multi-trait model, estimate genetic parameters, and select flood-irrigated rice genotypes with better genetic potentials in different evaluation environments. For this, twenty-five rice genotypes and six traits belonging to the flood-irrigated rice improvement program were evaluated. The experimental design used in all experiments was a randomized block design with three replications. The Monte Carlo Markov Chain algorithm estimated genetic parameters and genetic values. The grain thickness trait was considered highly heritable, with a credibility interval ranging from: $${h}^{2}$$ : 0.9480; 0.9440; 0.8610, in environments 1, 2, and 3, respectively. The grain yields showed a weak correlation estimate between grain thickness and 100-grain weight, in all environments, with a credibility interval ranging from ( $$\rho$$ = 0.5477; 0.5762; 0.5618 and 0.5973; 0.5247; 0.5632, grain thickness and 100-grain weight, in environments 1, 2, and 3, respectively). The Bayesian multi-trait model proved to be an adequate strategy for the genetic improvement of flood-irrigated.

Germplasm variability-assisted near infrared reflectance spectroscopy chemometrics to develop multi-trait robust prediction models in rice.

Rice is a major staple food across the world in which wide variations in nutrient composition are reported. Rice improvement programs need germplasm accessions with extreme values for any nutritional trait. Near infrared reflectance spectroscopy (NIRS) uses electromagnetic radiations in the NIR region to rapidly measure the biochemical composition of food and agricultural products. NIRS prediction models provide a rapid assessment tool but their applicability is limited by the sample diversity, used for developing them. NIRS spectral variability was used to select a diverse sample set of 180 accessions, and reference data were generated using association of analytical chemists and standard methods. Different spectral pre-processing (up to fourth-order derivatization), scatter corrections (SNV-DT, MSC), and regression methods (partial least square, modified partial least square, and principle component regression) were employed for each trait. Best-fit models for total protein, starch, amylose, dietary fiber, and oil content were selected based on high RSQ, RPD with low SEP(C) in external validation. All the prediction models had ratio of prediction to deviation (RPD) > 2 amongst which the best models were obtained for dietary fiber and protein with R2 = 0.945 and 0.917, SEP(C) = 0.069 and 0.329, and RPD = 3.62 and 3.46. A paired sample t-test at a 95% confidence interval was performed to ensure that the difference in predicted and laboratory values was non-significant.

New insight into the pigmented rice of northeast India revealed high antioxidant and mineral compositions for better human health

Northeast (NE) India possesses a rich diversity of rice cultivars including pigmented and non pigmented varieties. The pigmented rice is reported to possess a considerable amount of antioxidant compounds, free radical scavengers etc. In this study, eleven (black, red and white) rice cultivars of NE India were analyzed for antioxidant potentials, mineral and protein contents. Total phenolic content ranged from 94.8 (Idaw) to 900.90 mg GAE/100 g (Lumre). Total flavonoid content varied from 3.46 (Idaw) to 286.76 mg QE/100 g (Menil mibabaret). Total anthocyanin content varied from 0.23 (Farel) to 93.52 mg/100 g (Chakhao poireiton). The pigmented rice is also good sources of Catalase (CAT), Ascorbate peroxidase (APX) and Superoxide Dismutase (SOD) that can significantly reduce stress oxidative reactions. Chakhao poireiton possessed the highest Ni and Mn content, Tsulu tsuk had the highest Zn content, while Fazu and Tasung contained the highest Fe and Ca. The highest total protein was found in Chakhao poireiton (11.06%). And all the cultivars were found to be aromatic. Fourier Transformed Infra-Red spectroscopy (FTIR) identified various signature peaks and could discriminate the cultivars into pigmented and non pigmented. Principle Component Analysis (PCA) revealed the grouping of the cultivars based on the functional groups present. The present study could provide a better understanding of choosable rice lines for human consumption and also as germplasm resources for future rice improvement programs.

Agro-Morphological Characterization and Diversity Assessment of Rice Landraces in Nepal

Plant genetic resources are raw materials and their use in breeding is one of the most sustainable ways to conserve agro-biodiversity. Field research was conducted at National Agriculture Genetic Resources Centre (NAGRC) during 2018 & 2019 with the objective of agro-morphological characterization and diversity assessment of rice landraces. Forty-two landraces collected from 21 districts of Nepal were characterized and evaluated by using non replicated row design. The phenotypic diversity was assessed based on fourteen qualitative and thirteen quantitative characters following the descriptors developed by Bioversity International, IRRI and WARDA. Basic statistics were calculated by using Excel 2016 and UPGMA clustering and PCA was done with MINITAB-17. The diversity index (H') and coefficient of variation for different traits ranged from 0.16-0.96 and 8.00-47.77 respectively. Clustering grouped the landraces into four clusters with minimum similarity level of 46.33%. Landraces of cluster three i.e. NGRC01917, NGRC03034, NGRC03395, NGRC03057, NGRC03163 are found to be superior in terms of maturity days and yield. PCA partitioned the total variation into three principal components contributing 75.5% of the cumulative variance. Thus, the present study is the preliminary picture for characterization and diversity analysis in Nepalese rice landraces that can be used by the breeder in rice improvement program.

OsFBK4, a novel GA insensitive gene positively regulates plant height in rice (Oryza Sativa L.)

Semi-dwarf is one of the most valuable agronomic characteristics for rice improvement programs because it affects lodging resistance and grain yield. In the present study, a semi-dwarf mutant, RE9586 , exhibits reduced plant height, panicle length and decreased grain yield. Scanning electron microscopic observation results showed that the longitudinal length of the uppermost internode of RE9586 significantly reduced, resulting in a semi-dwarf phenotype. Employing a MutMap-based strategy, LOC_Os02g11790 was preliminarily identified as the candidate gene, which encoded the F-box domain and kelch repeat-containing protein ( OsFBK4 ). A point mutation in the 3rd exon of OsFBK4 resulted in an amino acid change of 414 R→G that was subsequently confirmed by linkage analysis. Real time-PCR showed the OsFBK4 gene was predominantly expressed in the internode. The knockout lines of OsFBK4 by CRISPR/Cas9 showed a short plant height, while OsFBK4 overexpression lines recovered the phenotype of plant height. We have also demonstrated that the expressions of GA-signaling genes such as SRL1 , CIGR , GID1 , GID2 , D1 , and SPY showed clear differences in which SRL1 was down regulated, while other genes were up-regulated in RE9586 mutant. GA biosynthesis genes, OsKAO , OsGA3ox2 , and OsGA2ox2 , also displayed apparent differences in expression level. In addition, the OsFBK4 protein probably localized to the nucleus and plasma membrane. In conclusion, OsFBK4 regulates plant height involving in GA signaling, providing further insights into the mechanisms underlying the regulation of plant height in rice.

Character Association of Yield and Yield Components of Various Varieties of Rice (Oryza sativa L.)

Yield and yield attributing parameters are the most widely targeted traits in rice improvement programmes. The relationship between yield and yield attributing traits are important for direct and indirect selection of traits which contribute to yield. Information on the extent of association between yield and yield components is important in the simultaneous improvement of correlated traits. This study was carried out to determine the direct and indirect contributions of yield components to yield of rice and the level of association. Path Coefficient Analysis was used to evaluate the character association of yield and yield components of twenty-five rice varieties at the Rivers State University Teaching and Research Farm, Port Harcourt, during the 2019 planting season under rainfed condition and complimented by irrigation in two different planting dates. The experiments were laid out in a randomized complete block design. Data were collected on yield and yield components. Leaf area, plant height, panicle length, panicle number, panicle weight, 100-grain weight and spikelet fertility correlated positively and significantly with grain yield per stand. The path coefficient analysis indicated that panicle number (0.265) and spikelet fertility (0.219) had the highest positive direct effect on grain yield per stand. Conversely, number of grains per panicle (-0.128), days to 50% flowering (-0.114), tiller number (-0.095) and panicle length (-0.056) exerted negative direct effect on grain yield per stand with 0.674 residual effects. Therefore, direct selection for leaf area, plant height, panicle number, panicle weight, 100 grain weight, and spikelet fertility will effectively improve yield in rice. Key words : Grain yield, Character Association, Oryza sativa, variation, yield components DOI: 10.7176/JNSR/13-8-02 Publication date: April 30 th 2022