Development of high yielding backcross inbred lines stacked with drought yield QTLs in rice (Oryza sativa L.)

Abstract

The present study entitled “Development of high yielding backcross inbred lines stacked with drought yield QTLs in rice (Oryza sativa L.)” was carried out at the Department of Genetics and Plant Breeding, College of Agriculture, Vellayani during 2022-2024 with an objective to identify high yielding drought tolerant rice lines from BC₂F₃ lines of Manu Ratna stacked with drought yield QTLs. The BC₂F₃ population used in the study were derived from the cross between Manu Ratna and Improved White Ponni stacked with drought yield QTLs qDTY ₁.₁ and qDTY₁₂.₁ developed as a part of PhD project of this department. The field evaluation was conducted at Integrated Farming System Research Station, Karamana where BC₂F₃ lines were screened under water stress conditions. In the laboratory experiments, the selected BC₂F₃ lines were analysed for biochemical and physiological characteristics and the BC2F4 lines were further screened for drought stress tolerance using PEG 6000. One thousand fifty BC₂F₃ plants from 10 different families, along with parents Manu Ratna and Improved White Ponni, were raised in family block design with three replications for each family. Water was withheld for fourteen days to induce drought stress during panicle initiation stage. Biometric observations were recorded from 210 BC₂F₃ plants, selected based on early flowering, plant height, higher number of productive tillers and leaf rolling score. Analysis of variance showed significant differences between the families. Based on plant height, earliness of flowering, number of productive tillers and leaf rolling score, 20 plants were selected. Among these, MIB29-2-3-1, MIB-29-2-3-21, MIB-29-8-4-4, MIB-29-8-5-10, MIB-29-8-5-30, MIB-29-85-35 and MIB-84-3-3-4 showed superior performance for yield traits viz. number of productive tillers per plant, panicle length, number of spikelets per panicle, number of filled grains per panicle, grain yield per plant, 1000 grain weight, grain length and grain width. The selected 20 plants of BC₂F₃ generation were analysed for biochemical and physiological parameters viz relative water content, cell membrane stability index, total chlorophyll content, proline content and peroxidase activity. Analysis of variance showed significant differences among the selected lines for these biochemical and physiological parameters. Among the lines, MIB-29-8-5-35, MIB-29-2-3-1, MIB-84-3-3-4, MIB-119-5-7-33 and MIB-29-8-5-10 showed superior performance for all biochemical and physiological characters. Seeds from the selected superior 20 BC₂F₃ plants were further screened for drought stress tolerance at different PEG 6000 concentrations. The experiment was conducted using factorial completely randomized design with two factors and three replications. The main factor was 20 lines while the second factor was PEG concentrations with three levels (0, 10 and 15%). The observations on root length, shoot length and number of seeds germinated were observed. The computed parameters recorded include germination percentage, mean germination time, germination index, root shoot ratio, germination stress tolerance index, fresh weight stress tolerance index, dry weight stress tolerance index and seedling vigour index. The analysis of variance also showed a significant difference among the 20 lines for all the traits except mean germination time and root shoot ratio. Based on the mean performance of the lines under drought stress induced by PEG, MIB-29-2-3-1, MIB-29-8-5-35, MIB-43-5-3-66 and MIB-119-5-7-33 were found to have seedling stage drought stress tolerance. High PCV and GCV were observed for the characters such as root length, shoot length, root shot ratio, germination stress tolerance index, dry weight stress tolerance index and seedling vigour index. Mean germination time showed a high PCV and a moderate GCV. The characters such as number of seeds germinated, germination per cent and germination index showed a moderate PCV and GCV. The characters viz. root length, shoot length, germination stress tolerance index, fresh weight stress tolerance index, dry weight stress tolerance index and seedling vigour index showed a high heritability along with high genetic advance, which indicated that selection based on these traits would be effective. Correlation analysis identified a significant positive genotypic and phenotypic correlation between root length, shoot length and fresh weight stress tolerance index with seedling vigour index. Path analysis showed that shoot length had a positive high direct effect on seedling vigour index and a high indirect effect on seedling vigour index through root length.Among the selected lines, MIB-29-2-3-1 and MIB-29-8-5-35 had higher yield, superior performance for biochemical and physiological character under field study and better seedling stage growth traits under PEG induced drought stress. Hence, these lines can be advanced to further generations through pedigree method of breeding for developing high yielding drought tolerant varieties. These lines can also be further advanced through backcross to develop bold red kernel rice varieties.