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The study entitled ‘Validation of quantitative trait loci (QTLs) for drought stress tolerance in RIL population of rice’ was conducted in the Department of Plant Breeding and Genetics, College of Agriculture, Vellayani and Rice Research Station, Vyttila, during the year 2022-2023, with an objective of validation of QTLs for drought resistance in RIL population developed from the cross between Sahbhagi Dhan and Jaya.
Rice varieties Sahbhagi Dhan (drought-tolerant), Jaya (drought-susceptible), and their twenty-eight F5 recombinant inbred lines (RILs) were used in the study. The study comprised of four major experiments. Experiment-I was conducted with the goal of validating the quantitative trait loci (QTL) associated with drought in the tolerant parent, employing specific SSR markers designed for drought. Twenty drought-specific SSR markers were used for the study. Presence of two qDTYs i.e., qDTY 1.1 and qDTY 3.1 for drought tolerance were validated using specific SSR markers viz., RM212 and RM520 respectively. All other markers used were monomorphic between Sahbhagi Dhan and Jaya.
The second experiment was evaluation of Polyethylene Glycol (PEG) induced drought stress tolerance at early seedling stage. Seeds were germinated in petri plates under varying PEG 6000 concentrations (0%, 5%, 10%, 15%, and 20%). The evaluation encompassed parameters such as germination percentage, survival percentage, as well as root and shoot lengths on the 15th day of PEG treatment. Sahbhagi Dhan demonstrated the highest germination and survival percentages, with the latter exceeding 60% even at the severe 20% PEG level. Conversely, Jaya exhibited the lowest percentages, even lower than all recombinant inbred line (RIL) populations. Notably, only Sahbhagi Dhan achieved germination surpassing 80% at 20% PEG level. RIL 2, 3, 15, 20, 21, 22, and 27 displayed germination percentages close to 80% at the same level.
At 20% PEG level, superior root lengths were exhibited by RIL 27 (9.90 cm) and RIL 3 (8.60 cm) compared to Sahbhagi Dhan (8.60 cm), whereas Jaya (3.25 cm) displayed the lowest, while RIL 20 and RIL 5 (8.50 cm) were on par with Sahbhagi Dhan. Maximum shoot lengths were exhibited by Sahbhagi Dhan (11.40 cm), while RILs such as 27, 3, 26, 22, and 16 showed performance on par with Sahbhagi Dhan. In contrast, Jaya (5.65 cm) recorded the lowest shoot length at different PEG levels.
In the third experiment, both the parents and twenty-eight RIL populations underwent evaluation for drought tolerance during the reproductive stage. Physiological, biochemical, and biometric traits were assessed during reproductive stage under drought and non-drought conditions using single-factor ANOVA in a completely randomized design (CRD) with two replications. The analysis of treatments under drought stress during the reproductive stage revealed significant differences in yield, as well as in morphological and physiological parameters. Drought stress led to a noteworthy reduction in chlorophyll content, relative water content, and cell membrane stability index. Conversely, biochemical traits, including proline content, superoxide dismutase, peroxidase, and catalase activity, exhibited a pronounced increase. Sahbhagi Dhan demonstrated superior results in biochemical traits, whereas certain recombinant inbred lines (RILs), namely 2, 3, 5, 13, 14, 15, 16, 20, 21, 22, 26, and 27, exhibited better outcomes compared to other RILs, however Jaya showed only marginal improvement under drought stress.
Physiological traits like leaf temperature and epicuticular wax content showed a slight increase under drought compared to the non-drought condition. Jaya (54.3) exhibited a higher stomatal frequency, whereas RIL 3 and 27 (41.3) and Sahbhagi Dhan (41.6) showed the lowest values while other RILs displayed intermediate values. The leaf rolling score was calculated according to the Standard Evaluation System (SES) scale ranging from 0 to 9 (IRRI, 2013). Jaya exhibited a high leaf rolling score of 7, whereas RILs such as 9, 12, 17, 18, 19, 23, 24, 25, and 28 displayed a leaf rolling score of 5. All other recombinant inbred lines, including Sahbhagi Dhan, exhibited a leaf rolling score of 3.
In the fourth experiment, validation was conducted to confirm the presence of two qDTYs, namely qDTY 1.1 and qDTY 3.1, associated with drought tolerance, utilizing specific SSR markers, namely RM212 and RM520, respectively. RM212 is linked to root depth, root volume, and relative water content during drought stress, while RM520 is associated with grain yield specifically under reproductive-stage drought stress. Among the twenty-eight RILs, twelve exhibited a banding pattern identical to Sahbhagi Dhan, while the rest displayed the banding pattern of Jaya for qDTY 1.1 using the marker RM212. For qDTY 3.1 using the marker RM520, all RILs, except for five recombinant inbred lines, exhibited a band like Sahbhagi Dhan. Recombinant inbred lines 2, 3, 5, 13, 14, 15, 16, 20, 21, 22, 26, and 27 possess both qDTY 1.1 and qDTY 3.1, whereas RILs such as 9, 12, 18, 19, and 28 lack both.
The findings of this study highlight the potential of the identified recombinant inbred lines, specifically 2, 3, 5, 13, 14, 15, 16, 20, 21, 22, 26, and 27, showcasing a promising combination of qDTY 1.1 and qDTY 3.1. Their exceptional performance across physiological, biochemical, and biometric traits, with a substantial impact on yield, especially in challenging conditions like severe drought, suggests their suitability for further evaluation and advancement in field trials. These lines hold significant promise for contributing to enhanced crop resilience and increased yield under adverse environmental conditions.