Spikelet Fertility Percentage Research Articles

Principal component analysis of morpho-floral traits in Oryza sativa × Oryza longistaminata advanced backcross lines of rice

Hybrid rice technology substantially improves the food security of South Asian countries where rice (Oryza sativa L.) is a staple food. Several traits contribute to hybrid seed production efficiency, among which stigma exsertion is crucial for enhancing production by facilitating out-crossing pollination. This study evaluated the variation patterns and relative impact of 12 morpho-floral traits on overall variability in advanced backcross lines derived from crosses CRMS 32B cv. Oryza sativa and Oryza longistaminata. For this study, 290 BC4F2 lines were grown during Kharif 2019 in 3 replications using a randomized complete block design (RCBD). Principle component analysis (PCA) was performed on all traits, and the findings revealed 11 principal components (PCs). Out of 11 PCs, the first five displayed eigenvalues exceeding 1, collectively explaining 78.78% of the total variability. PC1, PC2, PC3, PC4, and PC5 contributed 26.36%, 19.94%, 14.22%, 9.81%, and 8.44% of the variation, with eigenvalues of 3.16, 2.39, 1.71, 1.18 and 1.01, respectively. PC1 was predominantly associated with yield-related traits such as panicle length, plant height, grain yield per plant, grains per panicle, and effective tillers per plant. On the other hand, PC2 was mainly associated with outcrossing-related floral traits such as total stigma exsertion percentage, dual stigma exsertion percentage, and single stigma exsertion percentage. However, PC3 and PC4 were associated with both floral and yield-related traits, i.e., days to 50% flowering (DF), days to maturity (DM), plant height (PH), effective tillers per plant (ETPP), spikelet fertility percentage (SFP), grain yield per plant (GYPP) and grains per panicle (GPP). Therefore, PC1, PC2, PC3, and PC4 were major contributors to rice hybrid seed production.

Genetic Variability and Cause-Effect Relationship in Aromatic Rice

Twenty diverse rice genotypes, mostly aromatic landraces, were grown during warm wet season of 2022 to analyse the genetic variability, correlation and path coefficients for sixteen agro-morphological characters. The results of genotypic and phenotypic coefficients of variability, heritability, and genetic advance indicated that improvement through selection for flag leaf angle, panicle exertion, secondary branches per panicle, test weight, spikelet number, and number of filled grains would be effective. Correlation coefficients of grain yield with flag leaf area, spikelet fertility percentage, test weight and harvest index were positive and significant, while with flag leaf angle it was negative and significant indicating the importance of these characters on grain yield. Path analysis revealed that selection for larger flag leaf area, greater test weight and narrow flag leaf angle, reduced plant height and early flowering would increase grain yield. However, restrictions are required to be imposed on panicle number, panicle length and filled grain, so that a balance between morphological architecture and physiological rhythm is maintained to optimize source-sink relationship.

Combining Ability Studies of Promising Restorer Lines for Yield and Yield Components in Rice (Oryza sativa L.)

Background: The present inquisition was carried out at Regional Agricultural Research Station, Maruteru with a set of 30 experimental hybrids developed by crossing three male sterile lines with 10 testers in Line ´ Tester mating design during Kharif, 2022. Methods:The resultant 30 hybrids were studied in randomized block design with two replications along with the parents and hybrid check, HRI-174 during Rabi, 2022-23. Predominant non-additive gene action was found in the analysis of combining ability for lines, testers and line testers for grain production per plant, days to 50% flowering, days to maturity, ear bearing tillers per plant, filled grains per panicle and 1000-grain weight. Result:The results revealed RGL 5613 and MTU 2055 to be effective combiners for grain yield per plant, filled grains per panicle, spikelet fertility percentage and grain weight of one thousand grains. For five hybrids, the sca effects on grain yield per plant were large and favourable. These hybrids had recorded significantly higher grain yield perplant, more than 30 per cent, compared to the check, HRI-174, in addition to significant desirable sca effects for grain yield per plant.

Marker assisted pyramiding of qDTY QTLs governing yield under drought stress into rice variety ADT(R)45

Drought occurrence during reproductive stage of rice leads to significant yield loss. Rice production has to be doubled to feed the ever increasing human population. As the yield levels are stagnated under favourable production system, improvement of yield under unfavourable environment is key to attain the projected target. Therefore, the present study was undertaken to improve the drought tolerance of popular rice variety ADT(R)45 by introgressing major effect quantitative trait loci (QTLs) conferring yield under drought (qDTY1.1, qDTY3.1 and qDTY12.1) through marker assisted backcross breeding (MABB). Through MABB, 117 BILs in the background of ADT(R)45 were developed with different combinations of qDTY QTLs.  The BILs were evaluated under rainfed target production environment and observations on nine biometrical and yield traits were recorded. Variability analysis revealed presence of additive gene action for the traits viz., total number of tillers per plant, number of productive tillers per plant, hundred grain weight, yield per hectare and single plant yield. Hence, selection based on these traits will be effective to improve yield under drought stress. Association analysis showed total number of tillers per plant, number of productive tillers per plant, panicle length, hundred grain weight and spikelet fertility percentage were highly correlated with yield per plant. Comparison of BILs with different QTL combinations showed that BILs with single QTL (qDTY12.1) was better for most of the traits studied. BILs with single or two QTL combinations were found to perform better under rainfed condition, when compared to BILs with all the three QTLs. Keywords: Reproductive stage drought, Rainfed, qDTYs, rice, BILs, MABB

Identification of simple sequence repeat markers linked to heat tolerance in rice using bulked segregant analysis in F2 population of NERICA-L 44 × Uma.

The damage caused by high temperature is one of the most important abiotic stress affecting rice production. Reproductive stage of rice is highly susceptible to high temperature. The present investigation was undertaken to identify polymorphic microsatellite markers (SSR) associated with heat tolerance. The rice cultivars NERICA- L 44 (heat tolerant) and Uma (heat susceptible) were crossed to generate F1 and F2 populations. The F2 population was subjected to heat stress at >38°C and the 144 F2 plants were evaluated for their tolerance. The results note that the mean of the F2 population was influenced by the tolerant parent with regards to the traits of plant height, membrane stability index, photosynthetic rate, stomatal conductance, evapotranspiration rate, pollen viability, spikelet fertility and 1000 grain weight. Ten each of the extremely susceptible and tolerant plants were selected based on the spikelet fertility percentage. Their DNA was pooled into tolerant and susceptible bulks and Bulked Segregant Analysis (BSA) was carried out using 100 SSR markers to check for polymorphism. The survey revealed a polymorphism of 18% between the parents. RM337, RM10793, RM242, RM5749, RM6100, RM490, RM470, RM473, RM222 and RM556 are some of the prominent markers that were found to be polymorphic between the parents and the bulks. We performed gene annotation and enrichment analysis of identified polymorphic markers. Result revealed that the sequence specific site of that chromosome mostly enriched with biological processes like metabolic pathway, molecular mechanism, and subcellular function. Among that RM337 was newly reported marker for heat tolerance. Expression analysis of two genes corresponds to RM337 revealed that LOP1 (LOC_Os08g01330) was linked to high temperature tolerance in rice. The results demonstrate that BSA using SSR markers is useful in identifying genomic regions that contribute to thermotolerance.

Influence of Water Stress on Canopy Temperature and Yield Contributing Characteristics of Wet Seeded Rice

Canopy temperature (CT) is one of the indices for evaluating water stress. The study has been taken to correlate water stress with CT and to evaluate effect of water stress on crop and yield performance of wet seeded rice (WSR). The canopy temperature of rice at vegetative and flowering stages were investigated under different soil water stresses. The field experiment was conducted at IRRI (International Rice Research Institute) during dry season, 2011. Three levels of water stress (-10, -20 and -40 kPa) were applied at 3-leaf (3L) to panicle initiation (PI), PI to flowering (FL) and FL to physiological maturity (PM) stages. One non -stressed treatment, i.e., continuously flooded puddled transplanted rice (PTR-CF) was used as a control. Soil water tension was measured using a 30-cm long gauge tensiometer and a handheld infrared thermometer was used to measure CT. Canopy temperatures were recorded from 3L to PI and PI to FL stages. In both the stages, CT was within the range of marginal stress. Canopy temperature depression (CTD) was higher in the stressed condition than that of the nonstressed. At the PI stage, leaf area index (LAI) was significantly lower in WSR than PTR -CF. LAI was comparatively lower in WSR with -20 kPa and -40 kPa than WSR with -10 kPa and PTR-CF when water stress imposed during PI-FL. Decreasing grain yield was observed when irrigation threshold increased from -10 to -40 kPa during PI to FL and FL to PM, but the differences were not significant. Yield components of WSR with different stresses were not significantly different. But spikelet fertility (%) and grain weight (g) of WSR was significantly higher than that of PTR-CF. The yield of PTR-CF was similar to the yield of WSR. Panicle/m2 correlated negatively with CT under a stressed condition. Yield and all yield components ex cept spikelet per panicle were positively correlated with CT at 60 days after seeding (CT 60). Under stressed condition, CT correlated negatively with the grain yield. Results revealed that CT correlated positively with grain yield under non-stressed condition (CT35 and CT60). Spikelet fertility percentage (SF%) correlated negatively with CT35 and CT46. It has been concluded that CT and CTD may be used for water stress evaluation. Bangladesh Rice J. 25 (2) : 69-76, 2021

Variability, Correlation and Path Analysis for Several Quantitative Traits Derived Multi-Parent Advanced Generation Inter-Cross (Magic) F2 Population of Rice (Oryza sativa L.)

Eight quantitative traits of an F2 MAGIC population in rice were subjected to analyze variability, correlation and path analysis. The results of third and fourth degree statistics (skewness and kurtosis) showed that Individual dried straw weight, 1000-seed weight, Individual grain yield, and Number of effective tillers are associated with complementary gene interaction, requiring intense selection, while Plant height, Panicle length, Spikelet fertility percentage, and Harvest index are associated with duplicate (additive x additive) gene interactions, are suitable for mild selection. Leptokurtic distribution of Plant height, Number of effective tillers per plant, Pancile length and Spikelet fertility percentage revealed that the large number of genes in governing the traits. Platykurtic distribution of Individual dried straw weight, 1000-seed weight, Individual grain yield and Harvest index indicated fewer genes controlling the traits. However, when it comes to H2 and GAM, high values were seen in Number of effective tillers per plant, Individual dried straw weight, Individual grain yield, the traits could be explained by additive gene action and achieved through mass selection. High heritability and lower GAM of Plant height, Panicle length, 1000-seed weight and Harvest index indicated by non-additive genes with limiting the chances of direct selection. For the Pearson correlation, 1000-seed weight showed no correlation with other traits. Individual grain yield highly correlated with Number of effective tillers per plant (0.864**) and Individual dried straw weight (0.828**). The highest total effects on Individual grain yield were Number of effective tillers per plant (2.7437) and Individual dried straw weight (1.0865). Individual dried straw weight had highest direct effect on Individual grain yield at 1.0734, while most of the traits showed high indirect effect on Individual grain yield through Individual dried straw weight.

Genetic Architecture and Association Studies for Grain Yield and its attributing Traits in Recombinant Inbred Lines for Sodicity Tolerance in Rice (Oryza sativa L.)

The present study was undertaken at NSP Unit 6 Agricultural Research Farm and Main Experimental Station of Acharya Narendra Dev University of Agriculture and Technology, Uttar Pradesh, India, from July to November 2020, in which genetic variability and heritability of 250 recombinant inbred lines (F7) and their parents PUSA 44 and CSR 43 were evaluated and correlation studies were performed for grain yield and yield contributing traits. The experiment was conducted in two replications at two different and naturally occurring sodic conditions following α-lattice design. Analysis of variance revealed significant variations among the lines depicting inherent variability between lines. For attributes, viz., plant height, effective tillers plant-1, spikelet fertility percentage, test weight and grain yield plant-1, high phenotypic and genotypic coefficient of variation estimates were observed for both the locations indicating good scope for selection based on these traits. However, the attributes viz., test weight and effective tillers plant-1 values depicted the pertinent role of the environment and thus, require careful assessment in selection programs concerning these traits. For days to 50% flowering, filled grains panicle-1, spikelet fertility percentage, and grain yield plant-1, moderate heritability was discovered with a high genetic advance as a percentage of mean, indicating that there is less influence of environment over these traits. Correlation studies revealed a significant and positive association with these yield attributing traits. Mutual association between component traits exhibit variable responses at both locations, validating genotype and environment interactions among traits with respect to yield.

Phenotypic assessment of rice landraces for genetic variability and diversity studies under heat stress

The present investigation was carried out to estimate the genotypic and phenotypic variability, heritability, genetic advance and divergence based on heat stress and yield associated traits using 48 landraces of rice grown during rabi 2016 and 2017 at ICAR-Indian Institute of Rice Research farm, Hyderabad. ANOVA revealed the existence of significant differences for all the traits under study. Phenotypic coefficient of variation (PCV) was found slightly elevated than the genotypic coefficient of variation (GCV). All the characters under study except time to maturity exhibited high heritability coupled with high genetic advance as a per cent of mean, which revealed the predominance of additive gene action in controlling these traits. Cluster analysis grouped the 48 landraces into ten distinct clusters. Cluster I consisted of one landrace, while cluster II and III had 9 landraces each. Clusters IV, V, VI, VII, VIII, IX and X had 6, 2, 3, 3, 1, 6 and 8 landraces respectively. Cluster I included one landrace Byama Jhupi which was superior for the trait number of grains per panicle. Highest single plant yield (Mugei), fertility percentage (Neta) and time of heading (Neta) were recorded by entries of cluster II and highest panicle number per plant was recorded by landrace (Chiiti Mutyalu) of cluster IX. The genotypes of cluster II, VIII and IX showed high spikelet fertility percentage. Hence the genetic resources of these clusters can be utilized in the breeding programmes for development of heat tolerant varieties. The study helped to understand the extent of genetic diversity among the genetic resources which serve as a treasure of highly useful traits which can be exploited in developing high yielding and stress tolerant varieties.

Genetic Variability, Character Association and Path Analysis for Yield and its Related Traits in Rice (Oryza sativa L.) Genotypes

Assessment of variability and trait associations in a crop helps to enhance selection efficiency. With this objective, a study was conducted to estimate the genetic variability, character association and path coefficient analysis for grain yield and its component traits in 80 rice genotypes during Kharif-2020. Eighty genotypes including eight checks were evaluated in alpha lattice design with three replications. For all of the traits studied, the results revealed significant variance in all genotypes.PCV was found to be slightly more than the corresponding GCV for all the characters, indicating the role of environment in the expression of these traits. However, high GCV and high PCV were observed for number of effective tillers, grain yield per plot, number of filled grains per panicle, number of unfilled grains per panicle, biomass yield, harvest index, grain yield per plant and grain yield per hectare. Furthermore, all of the variables investigated had strong heritability and high genetic progress as a percentage of mean, with the exception of days to 50% blooming, days to maturity, and kernel breadth. Days to first flowering, days to 50% flowering, days to maturity, spikelet fertility percentage, number of filled grains per panicle, harvest index and kernel length showed a significant and positive association with grain yield per plot. Highest direct contribution to grain yield per plot was manifested by kernel length, harvest index and spikelet fertility percent. Days to first flowering, days to maturity, number of effective tillers, number of unfilled grains per panicle, test weight, biomass yield were also found to exert a positive effect on yield, thus can be considered as desirable traits for selection in high yielding genotypes.

Genetic Dissection of Yield Determinants in Advance Breeding Lines (ABLs) of Rice (Oryza sativa L.) under Irrigated Condition of Chhattisgarh, India

The present study was undertaken to study the extent of genetic variability, character association and path analysis in 53 irrigated late duration breeding lines for 12 quantitative and 10 quality parameters. Analysis of variance revealed the presence of significant variation among the breeding lines for all the characters except for total tillers per plant, effective tillers per plant, spikelet fertility percentage and grain yield per plant. The highest magnitude of PCV and GCV were displayed by grain yield per plant followed by harvest index, filled spikelet per panicle and 1000 seed weight. The greater extent of heritability in broad sense were recorded for days to maturity, days to 50% flowering, 1000 seed weight, plant height, total spikelet per panicle, kernel length, kernel L:B ratio, grain length, head rice recovery percentage, amylose content, hulling and milling percentage. However, high heritability coupled with high genetic advance as percent of mean were displayed by plant height, number of spikelet per panicle, filled spikelet per panicle,1000 seed weight, kernel length, kernel L:B ratio, grain length, head rice recovery percentage and amylose content. Grain yield per plant exhibited positive significant correlation with harvest index, effective tillers per plant, 1000 seed weight, spikelet fertility %, days to maturity and days to 50% flowering. Path analysis revealed direct effect on grain yield were exerted by days to 50% flowering followed by harvest index, 1000 seed weight, total tillers per plant, number of spikelet per plant, effective tillers per plant and plant height indicating their importance in rice breeding programs.

Principal Component Analysis for Yield and its Attributing Traits in Aromatic Landraces of Rice (Oryza sativa L.)

The present investigation was carried out in Kharif 2019 (July to November) to estimate the relative contribution of various traits for total genetic variability present in aromatic landraces by Principal Component Analysis. Here 90 aromatic rice landraces along with six check varieties were evaluated for 13 quantitative characters by Principal Component Analysis. Principal Component Analysis showed that, out of 13 quantitative characters studied, only five principal components (PCs) exhibited more than 1.00 eigen value and showed about 81.62% cumulative variability among the traits studied. Out of the five principal components exhibiting more than 1.00 eigen value PC1 had the highest variability (25.12%) followed by PC2 (21.8%). The first principal component PC1 was positively contributed mainly by two characters viz., Grain Length and 1000 grain weight. The second principal component PC2 was contributed mostly by three characters like grain yield plant-1, panicle weight and spikelet fertility percentage. The third principal component PC3 is positively associated with panicle weight, grain yield plant-1 and spikelet fertility percentage. The fourth principal component PC4 is positively associated with spikelet fertility percentage, Grain Length/ Breadth ratio and fertile grains panicle-1. The fifth principal component PC5 is positively associated with total grains per panicle-1, grain width and 1000 grain weight. All the principal components were showing positive contribution for yield and its attributing traits. These variations can be exploited in crop improvement programme for developing high yielding varieties.

High-density linkage mapping for agronomic and physiological traits of rice (Oryza sativa L.) under reproductive-stage salt stress

Rice is one of the most important cereals of the world, with a substantial amount of genetic variation, and a staple food for more than half of the world's population. Salinity is the second most important abiotic stress after drought that adversely affects rice production globally. Both the seedling and reproductive stages are extremely sensitive to salinity but tolerant at the reproductive stage which is most crucial, as it translates into grain yield. Therefore, it is more important to identify the underlying factors of tolerance at the reproductive stage as a necessary step towards improving varieties for salinity environments. However, because of the difficulties in phenotyping protocols of salinity tolerance screening at the reproductive stage, only a few studies exist on this aspect. In view of this, a study involving 188 F4 rice lines derived from a cross CSR28 × Sadri along with the parents was carried out for phenotyping using a novel screening approach for the reproductive stage in salinity conditions and genotyping by SNP markers (Infinium Illumina 6K SNP chip) to construct a high-saturation linkage map. Quantitative trait loci analysis in an F4 population for physiological traits (chlorophyll a, chlorophyll b and carotenoid) and agronomic traits (plant height, filled grain number, grain yield and spikelet fertility percentage) led to the identification of 14 QTLs with an LOD range of 2.72-4.46 explaining phenotypic variation of 5.29-24.86% on chromosomes 1, 2, 3, 5, 6, 7 and 8. Tolerant alleles were contributed by both CSR28 and Sadri. The results indicated that both physiological and agronomic traits were involved in salinity tolerance at the reproductive stage and majority of the QTLs identified in this study are reported for the first time.

Identification of novel QTLs for grain fertility and associated traits to decipher poor grain filling of basal spikelets in dense panicle rice

High grain number is positively correlated with grain yield in rice, but it is compromised because of poor filling of basal spikelets in dense panicle bearing numerous spikelets. The phenomenon that turns the basal spikelets of compact panicle sterile in rice is largely unknown. In order to understand the factor(s) that possibly determines such spikelet sterility in compact panicle cultivars, QTLs and candidate genes were identified for spikelet fertility and associated traits like panicle compactness, and ethylene production that significantly influences the grain filling using recombinant inbred lines developed from a cross between indica rice cultivars, PDK Shriram (compact, high spikelet number) and Heera (lax, low spikelet number). Novel QTLs, qSFP1.1, qSFP3.1, and qSFP6.1 for spikelet fertility percentage; qIGS3.2 and qIGS4.1 for panicle compactness; and qETH1.2, qETH3.1, and qETH4.1 for ethylene production were consistently identified in both kharif seasons of 2017 and 2018. The comparative expression analysis of candidate genes like ERF3, AP2-like ethylene-responsive transcription factor, EREBP, GBSS1, E3 ubiquitin-protein ligase GW2, and LRR receptor-like serine/threonine-protein kinase ERL1 associated with identified QTLs revealed their role in poor grain filling of basal spikelets in a dense panicle. These candidate genes thus could be important for improving grain filling in compact-panicle rice cultivars through biotechnological interventions.

Manipulation of Flowering Time to Mitigate High Temperature Stress in Rice (Oryza sativa L.)

Background: High temperature is an important abiotic stress affecting the productivity of rice. Early morning flowering trait is an escape mechanism from heat. This trait is present in wild rice cultivars. Here we tried to induce early morning flowering trait by the application of methyl jasmonate.Methods: A pot culture experiment was conducted during Rabi, 2017 and 2018 to study the effect of foliar application of methyl jasmonate on high temperature stress (more than 35°C) mitigation in rice was conducted in the Department of Plant Physiology, College of Agriculture, Vellayani during 2017-2019. The variety used was Uma (MO 16). Methyl jasmonate was applied as foliar spray to the spikelet in varying concentration with different time. Physiological observations were taken at 50% flowering stage and yield parameters were taken at harvest stage. Conclusion: There was significant variation for physiological and yield components among treatments. 4mM L-1 methyl jasmonate at 7am treatment exhibited increase in pollen viability, spikelet fertility percentage, yield per plant and 1000 grain weight. Hence, it is found that methyl jasmonate can advance anthesis time and thereby plants can escape from the severity of temperature experiencing at the normal flowering time in rice.

Molecular tagging of Rf genes for the fertility restoration of WA-CMS system by bulk segregant analysis in rice

The process of screening for fertility restoration trait involves test crossing with a set of cytoplasmic male sterile (CMS) lines and evaluation of F1 hybrids for pollen and spikelet fertility. In the present study, F2 mapping population derived from a cross, APMS 6A × RP 5933-123 was utilized to map Rf genes. The F2 population was also genetically analysed for pollen and spikelet fertility percentage. Chisquare (?2) analysis to showed that the fertility restoration trait followed expected digenic ratio. By bulk segregant analysis (BSA) likely Rf genes containing regions were located on chromosome 10. The SSR markers viz., RM304, RM258 located on chromosome 10 and RM23958 located on chromosome 9 showed clear polymorphism between two groups of fertile and sterile bulks. Based on BSA linkage analysis and F2 population, pollen and spikelet fertility analysis along with molecular screening results of Rf linked markers, it is concluded that Rf4 gene located on chromosome 10 is playing major role and contributing to 90% of fertility restoration trait of newly derived restorer line RP5933 along with minor effect genes from chromosome 9. The findings may be useful for rice hybrid breeding.

Genetic diversity and population structure analysis of bold type rice collection from Southern India

It is essential to elucidate genetic diversity and relationships among related varieties of origin and landraces for improving the breeding process. Since rice breeding has improved agronomic traits such as yield and eating quality during green revolution, modern rice varieties are originated from narrow genetic resource and closely related. To resolve the population structure and genetic diversity in bold type rice varieties of southern India, we used a total of 81 rice genotypes by 100 simple sequence repeat markers composed of 36 improved varieties and 45 landraces, which are representative and important for bold type grain rice breeding. The landraces exhibit greater gene diversity than improved lines, suggesting that landraces can provide additional genetic diversity for future breeding. Clustering by Ward method was done to establish a relationship among the 81 rice genotypes. All the genotypes were clustered into mainly 5 clusters. Principle component analysis revealed that the first principal component revealed 42.87% variation, while the second component showed 14.01% variation. Among the eight morpho-physiological and plant production traits studied, the relative water content and spikelet fertility percentage contributed towards maximum diversity. Principle co-ordinate analysis evidently differentiated the genotypes to high yielding varieties with common ancestry. Population structure analysis also obviously classified the genotypes into high yielding susceptible and indigenous tolerant groups. These old varieties and landraces present in crop germplasm collections represent a strategic reserve of genetic variation that can be tapped for varieties and understanding of stress response and developing new varieties that are physiologically adapted to highly variable, climate-resilient environments.

Two dimensional in-vitro phenotyping of root system architecture using Poly Ethylene Glycol in backcross inbred lines harboring drought tolerant QTLs of rice (Oryza sativa L.)

The present investigation was made to validate the effect and expression of multiple drought QTLs from Apo in the background of high yielding drought susceptible variety IR 64 under two dimensional in-vitro root architecture studies. The genotype CB 229 (DTY2.2, DTY3.1 and DTY8.1) recorded a higher network bushiness, network width, specific root length and network distribution of roots under PEG treatment (stress) and in network area CB 193-3 outperformed than CB 229. This clearly shows that introgression of multiple drought QTLs in various combination in the same genetic background enhances different level of expression of QTLs and tolerance to varied intensity of drought. Under field screening for drought, CB 229 out performed in both spikelet fertility percentage and yield than the remaining BILs. The traits viz., major ellipse axis, maximum number of roots, network bushiness, specific root length, network convex area and network width are positively correlated with spikelet fertility percentage and single plant yield under drought experiment. Principal component analysis accounted for 78.47 per cent of variability among root traits in PC1 and was loaded with all the traits observed under in-vitro condition. Hence, an understanding on complex nature of QTL expression associated with root system architecture under in-vitro stress in rice may help the breeder to develop new cultivars with enhanced level of tolerance against water limited situations in near future.

Study of genetic divergence in rice (Oryza sativa L.) genotypes with high grain zinc using Mahalanobis’ D2 analysis

The present investigation was conducted with twenty-two genotypes of rice during Kharif, 2018 in RBD with three replications in five different locations. The 22 rice genotypes were characterized based on 16 quantitative traits viz., days to first flowering, days to 50 per cent flowering, days to maturity, the total number of effective tillers per plant, plant height (cm), panicle length (cm), the number of spikelets per panicle, the number of grains per panicle, spikelet fertility percentage, grain weight per panicle (g), grain yield per plant (g) , 1000-grain weight (g), grain yield per plot (kg), grain yield per hectare (kg), grain L/B Ratio, grain zinc content (ppm or mg /kg) using Mahalanobis D2 statistic. D2 analysis distributed the 22 genotypes into six clusters, of which cluster I was the largest with 15 genotypes. Cluster II had maximum intra-cluster values of 5.16 and the maximum inter-cluster distance was observed between the clusters III and V (40.51) followed by cluster IV and V (28.39) indicating the importance of the genotypes present in these clusters for exploiting heterosis for the desirable traits of these clusters.

Genetic variability and association studies in F2 population of rice under sodicity

Rice is the major staple food crop in Asia and it feeds more than 70 per cent population of India. A study was carried out in rice using F2 segregating population of three cross combinations viz., ASD 16 × CSR 23, ASD 16 × Anna (R) 4 and MDU 6 × Ezhome1 in a non-randomized experimental design under sodic soil condition. Observations were recorded on 12 morphometric traits viz., days to flowering, plant height, flag leaf length, flag leaf width, number of productive tillers, panicle length, number of grains per panicle, spikelet fertility percentage, chlorophyll content, thousand grain weight, grain length breadth ratio and single plant yield. Genetic variability parameters and correlation varied from cross to cross and the traits number of productive tillers and number of grains per panicle showed high PCV and GCV. These characters also showed high positive correlation towards single plant yield with high direct effects in path analysis. Hence, these traits could be relied upon as selection indices under sodic soil conditions in rice.