Evaluation of rice genotypes for brown planthopper (BPH) resistance using molecular markers and phenotypic methods

Twenty eight (28) rice genotypes were used to evaluate the genetic variability based on known BPH resistant loci spread through most of the genome (chromosomes 2, 3, 4, 5, 6, 8, 10, 11 and 12), using closely linked simple sequence repeat (SSR) markers and by different phenotypic screening methods. A total number of 155 alleles were detected by 30 polymorphic markers with an average of 4.6 per locus. The genetic diversity, polymorphic information content (PIC) ranged from 0.15 to 0.89 and 0.13 to 0.88, respectively and the allele frequency ranged from 0.21 to 0.89. These microsatellite markers linked to BPH resistance loci classified rice genotypes into three clusters with additional sub groups and sub sub groups. Our study reveals high genetic variation and clear genotypic relationship for BPH resistance based on BPH resistance linked markers and known phenotypic screening methods such as standard seedbox screening technique, honey dew test and nymphal survival method. Phenotypic evaluation showed clear distinction between resistant and susceptible type by clearly revealing moderately resistant types as well. Combined use of phenotypic and genotypic evaluation methods can improve the efficiency of marker assisted selection and utilization of resistant genotypes for crop improvement by rice breeders.Keywords: Nilaparvata Lugens, microsatellite markers, polymorphism, genetic diversityAfrican Journal of Biotechnology Vol. 12(19), pp. 2515-252

Heritability, Correlation and Path Analysis among Yield and Yield Attributing Traits for Drought Tolerance in an Interspecific Cross Derived from <i>Oryza sativa x O. glaberrima </i>Introgression Line under Contrasting Moisture Regimes

Drought is a major constraint for rainfed lowland and upland rice productivity throughout world. A backcross inbred population derived from ‘Swarna’ and ‘WAB450-I-B-P-157-2-1’ (Oryza sativa L. x O. glaberrima) was evaluated under both irrigated and lowland drought stresses for yield and yield related traits across three different seasons. Significant differences were found among all the analyzed traits. Coefficients of variation were recorded relatively high for filled grains per panicle, spikelet fertility, test weight, harvest index and grain yield and low for panicle length under both conditions during the study interval. Broad sense heritability varied from 0.28 (panicle number) to 0.83 (plant height) under stress and 0.31 (test weight) to 0.86 (plant height) under control. However, heritability estimates for grain yield and harvest index were found to be similar under both conditions. Traits such as filled grains per panicle, spikelet fertility, harvest index and grain yield recorded higher values of both heritability, as well as genetic advance under both conditions, indicating the suitability of these traits as selection criteria to derive high yielding genotypes for drought prone regions. Harvest index exhibited maximum positive direct effect on grain yield under both the conditions; in addition, filled grains per panicle, spikelet fertility and biomass had positive direct effect on grain yield under both irrigated and lowland drought stresses state. Hence, for improving the rice yield under lowland drought ecology, a genotype should posses a large number of panicles per plant, filled grains per panicle, high spikelet fertility and maintains higher biomass and harvest index

Evaluation of Rice Recombinant Inbred Lines Developed from the Cross Rasi × Improved Samba Mahsuri for Drought Tolerance

Drought has been one of the most important limiting factors for rice productivity, particularly in the rainfed ecosystem. It is important to understand the genetic basis of drought tolerance in donor lines and develop drought tolerant rice cultivars, based on this information. We earlier identified the rice line, Rasi as tolerant to drought and developed a recombinant inbred line (RIL) mapping population consisting of 209 lines. These lines along with their parents were grown under well-watered and drought stress conditions in a two-year experiment (wet season 2020 and 2021) with drought stress imposed during reproductive stage. The study revealed high genetic variability for 12 key agro morphological traits associated with drought tolerance among the RILs.  Of the 209 RILs, 59 showed superior performance over the checks and even the tolerant parent, Rasi under severe drought condition. Two RILs, RIL-33 and RIL-58 showed exceptional drought tolerance along with greater plot yield and grain weight under drought condition and they possessed medium slender grain type. These two lines can be a new novel genetic resource for drought tolerance in breeding programmes.&nbsp

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Not AvailableAbstract Background: Rice, a major food crop of the world, endures many major biotic stresses like bacterial blight (BB), fungal blast (BL) and the insect Asian rice gall midge (GM) that cause significant yield losses. Progress in tagging, mapping and cloning of several resistance (R) genes against aforesaid stresses has led to marker assisted multigene introgression into elite cultivars for multiple and durable resistance. However, no detailed study has been made on possible interactions among these genes when expressed simultaneously under combined stresses. Results: Our studies monitored expression profiles of 14 defense related genes in 11 rice breeding lines derived from an elite cultivar with different combination of R genes against BB, BL and GM under single and multiple challenge. Four of the genes found implicated earlier under combined GM and BB stress were confirmed to be induced (≥ 2 fold) in stem tissue following GM infestation; while one of these, cytochrome P450 family protein, was also induced in leaf in plants challenged by either BB or BL but not together. Three of the genes highlighted earlier in plants challenged by both BB and BL were also found induced in stem under GM challenge. Pi54 the target R gene against BL was also found induced when challenged by GM. Though expression of some genes was noted to be inhibited under combined pest challenge, such effects did not result in compromise in resistance against any of the target pests. Conclusion: While R genes generally tended to respond to specific pest challenge, several of the downstream defense genes responded to multiple pest challenge either single, sequential or simultaneous, without any distinct antagonism in expression of resistance to the target pests in two of the pyramided lines RPNF05 and RPNF08.ICAR-NAS

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Not AvailableDrought has been one of the most important limiting factors for rice productivity, particularly in the rainfed ecosystem. It is important to understand the genetic basis of drought tolerance in donor lines and develop drought tolerant rice cultivars, based on this information. We earlier identified the rice line, Rasi as tolerant to drought and developed a recombinant inbred line (RIL) mapping population consisting of 209 lines. These lines along with their parents were grown under well-watered and drought stress conditions in a two-year experiment (wet season 2020 and 2021) with drought stress imposed during reproductive stage. The study revealed high genetic variability for 12 key agro morphological traits associated with drought tolerance among the RILs. Of the 209 RILs, 59 showed superior performance over the checks and even the tolerant parent, Rasi under severe drought condition. Two RILs, RIL-33 and RIL-58 showed exceptional drought tolerance along with greater plot yield and grain weight under drought condition and they possessed medium slender grain type. These two lines can be a new novel genetic resource for drought tolerance in breeding programmes.Not Availabl

Not Available

Not AvailableBackground: Rice, a major food crop of the world, endures many major biotic stresses like bacterial blight (BB), fungal blast (BL) and the insect Asian rice gall midge (GM) that cause significant yield losses. Progress in tagging, mapping and cloning of several resistance (R) genes against aforesaid stresses has led to marker assisted multigene introgression into elitecultivarsformultipleanddurableresistance.However, no detailed study has been made on possible interactions among these genes when expressed simultaneously under combined stresses. Results: Our studies monitored expression profiles of 14 defense related genes in 11 rice breeding lines derived from an elite cultivar with different combination of R genes against BB, BL and GM under single and multiple challenge. Four of the genes found implicated earlier under combined GM and BB stress were confirmed to be induced (≥ 2fold)instem tissue following GM infestation; while one of these, cytochrome P450 family protein, was also induced in leaf in plants challenged by either BB or BL but not together. Three of the genes highlighted earlier in plants challenged by both BB and BL were also found induced in stem under GM challenge. Pi54 the target R gene against BL was also found induced when challenged by GM. Though expression of some genes was noted to be inhibited under combined pest challenge, such effects did not result in compromise in resistance against any of the target pests. Conclusion: While R genes generally tended to respond to specific pest challenge, several of the downstream defense genes responded to multiple pest challenge either single, sequential or simultaneous, without any distinct antagonism in expression of resistance to the target pests in two of the pyramided lines RPNF05 and RPNF08.National Agricultural Science Fun

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Not AvailableMTU1010 is a high-yielding mega-variety of rice grown extensively in India. However, it does not perform well in soils with low phosphorus (P) levels. With an objective to improve MTU 1010 for tolerance to low soil P, we have transferred Pup1, a major quantitative trait locus (QTL) associated with tolerance from another mega-variety, Swarna, through marker-assisted back cross breeding (MABB). Foreground selection of the F1 and backcross plants was performed with the codominant, closely linked CAPS marker, K20-2, while two flanking markers RM28011 and RM28157 were utilized for recombinant selection. At each backcross generation, positive plants were also analyzed with a set of 85 parental polymorphic SSR markers to identify theQTL-positive plants possessing maximum introgression of MTU 1010 genome. At BC2F1, the best backcross plant was selfe dtogenerate BC2F2s. Among them, the plants homozygous for Pup1 (n = 22) were reconfirmed using the functional marker for Pup1, viz., K46-1, and they were advanced through pedigree method of selection until BC2F6 generation. A total of five elite BC2F6 lines, possessing Pup1 and phenotypically similar to MTU 1010, were screened in the low soil P plot and normal plot (with optimum soil P levels) during wet season, 2016. All the selected lines showed better performance under low P soil with more number of productive tillers,better root system architecture,and significantly higher yield (>390%) as compared to MTU 1010. Further, under normal soil, the lines were observed to be similar to or better than MTU 1010 for most of the agro-morphological traits and yield. This study represents the successful application of marker assisted selection for improvement of tolerance to low soil P in a high-yielding Indian rice variety.The authors received financial support provided by the Department of Biotechnology (DBT), Government of India, for execution of the research study through the Grant # BT/PR4665/AGII/106/854/2012 dated: 19/02/2013