Phenotyping of rice germplasm for physiological traits suitable for dry direct seeded rice

Introduction

Rice (Oryza sativa L.) is one of the most important food crops and a major staple in India. Conventional transplanted rice is water-and labour-intensive, whereas dry direct-seeded rice (DSR) offers advantages such as reduced labour and water requirements. However, successful crop establishment and productivity under dry DSR depend on the availability of genotypes with suitable physiological and adaptive traits. Rapid germination, vigorous seedling growth, favourable root and shoot development, efficient biomass accumulation, water relations and photosynthetic activity are important characteristics for adaptation to dry DSR conditions. Therefore, phenotyping diverse rice germplasm for these traits can help identify genotypes with superior establishment, physiological performance and yield potential under DSR conditions. The identification of suitable physiological traits is particularly important for developing rice cultivars adapted to resource-conserving and moisture-limited production systems. Traits such as germination percentage, seedling vigour, root length, relative water content, leaf area index, growth rates, photosynthetic rate, transpiration rate and stomatal conductance can provide useful indicators of plant performance. Evaluation of genetic variability and estimation of heritability and genetic advance can assist in identifying traits amenable to selection, while correlation and path coefficient analyses can reveal traits associated with grain yield. Hence, the present study was undertaken to phenotype diverse rice germplasm for physiological traits suitable for dry DSR and to identify promising genotypes for further evaluation and use in DSR-oriented breeding programmes.

Materials and methods

The experiment was conducted during Kharif 2025 at the Regional Agricultural Research Station, Karjat, District Raigad, Maharashtra, under dry direct-seeded rice conditions. The experiment comprised 50 diverse rice genotypes and three checks, viz., Sahbhagi Dhan, N-22 and DRR Dhan 71, evaluated in an Augmented Block Design with five blocks. The plot size was 2.0 × 0.40 m (0.80 m 2 ) with a spacing of 20 × 10 cm, and sowing was carried out on 1 July 2025. Observations were recorded periodically up to physiological maturity for 27 germination, seedling, vegetative, reprod uctive, yield and physiological traits, including germination percentage, shoot and root length, seedling vigour index, plant height, relative water content, leaf area index, growth rates, dry matter accumulation, yield attributes, grain and straw yield, harvest index, specific leaf weight, specific leaf area, photosynthetic rate, transpiration rate, stomatal conductance and spikelet fertility. The recorded data were subjected to analysis of variance appropriate for the Augmented Block Design. Genotypic and phenotypic coefficients of variation (GCV and PCV), broad-sense heritability, genetic advance and genetic advance as per cent of mean (GAM) were estimated to assess the magnitude and nature of genetic variability. Phenotypic and genotypic correlation coefficients were calculated to determine associations among traits, while path coefficient analysis was performed to assess the direct and indirect effects of component traits on grain yield. Statistical analyses were carried out following the standard procedures of Panse et al. (1985) [1] .

Results and discussion

The present investigation, entitled "Phenotyping of Rice Germplasm for Physiological Traits Suitable for Dry Direct-Seeded Rice (Oryza sativa L.)", was carried out at the Regional Agricultural Research Station, Karjat, Dist. Raigad, during Kharif 2025 to phenotype 53 rice genotypes (50 test entries and 3 released checks -Sahbhagi Dhan, N-22 and DRR Dhan 71) evaluated in an Augmented Block Design (five blocks) for 31 germination, seedling, vegetative, reproductive, yield and physiological traits. The results are presented and discussed under the following heads: (i) analysis of variance, (ii) mean performance and range of variability, (iii) genetic parameters of variability, (iv) correlation studies, (v) path coefficient analysis, and (vi) identification of promising genotypes.

Analysis of variance

Treatment (genotypes + checks) mean squares were significant for the great majority of the 31 traits studied -including germination percent, seedling vigour index, plant height at all three growth stages, filled grains per panicle, spikelet fertility, test weight, grain yield per plant, straw yield per plant and harvest index -confirming the presence of wide and significant genetic variability in the germplasm and its suitability for phenotypic characterisation and selection. Mean squares due to genotypes alone were significant for most traits, while the checks-vs-genotypes component was significant for several key traits, reflecting a real difference in performance between the released checks and the test entries. Traits such as harvest index, grain yield, straw yield and net assimilation rate showed non-significant or comparatively weaker genotypic differences, indicating the need for a larger, replicated trial to fully resolve genotype effects for these traits (Table 1).

Mean performance and range of variability

A wide range of expression was recorded for most characters, indicating substantial diversity in the test material (Table 2). Seedling vigour index (2030.74-8550.50), grain yield per plant (12.78-29.52 g) and filled grains per panicle (48.80-148.80) showed particularly wide ranges. Coefficients of variation were comparatively high for seedling-stage traits (germination percent, seedling vigour index, root length) and for physiological traits (photosynthetic rate, net assimilation rate, transpiration rate), pointing to considerable scope for selection at the seedling and physiological-trait level -an outcome of particular relevance for early-stage screening under dry direct-seeded rice (DSR). High GCV, PCV and heritability coupled with high genetic advance as per cent of mean (GAM) were recorded for seedling vigour index, specific leaf area and germination percent, indicating that these traits are governed largely by additive gene action and are reliable for early-stage selection under dry DSR (Table 3; Fig. 1). Plant height at the three growth stages, filled grains per panicle and number of panicles per m 2 also combined high heritability with moderate-to-high genetic advance. In contrast, harvest index, transpiration rate, photosynthetic rate and stomatal conductance showed low estimates of heritability along with a comparatively wider gap between PCV and GCV, suggesting greater environmental influence and the need for replicated evaluation before these traits can be used as direct selection criteria.

Genetic parameters of variability

Correlation studies

Correlation analysis was carried out to detect the association of genotype performance with grain yield through the physiological and root/seedling traits with yield. Stomatal conductance and transpiration rate emerged as the strongest physiological correlates of grain yield at both the phenotypic and genotypic levels, exceeding even photosynthetic rate itself, followed by absolute growth rate and net assimilation rate (Table 4; Fig. 2). Specific leaf area and seedling vigour index showed negligible or negative association with grain yield at the whole-trial level. Root length (r = 0.720**) and seedling vigour index (r = 0.550**) showed strong, statistically significant positive correlation with grain yield, indicating that seedling-stage root vigour is closely linked with final productivity and can be used as an early, non-destructive selection criterion under dry DSR conditions (Table 5). The complete pairwise correlation matrices among all physiological, seedling and root traits, from which Tables 4 and5

Conclusion

Association analysis identified root length and seedling vigour index as important early-stage traits associated with grain yield, with root length showing a strong positive correlation with grain yield (r = 0.720). Among the physiological traits, stomatal conductance and transpiration rate showed the strongest positive associations with grain yield at both phenotypic and genotypic levels, while net assimilation rate, photosynthetic rate and absolute growth rate also contributed positively. Path coefficient analysis further highlighted stomatal conductance as an important direct contributor to grain yield, supporting its potential value as a physiological selection criterion under the conditions of the present study.

Based on superior grain yield combined with favourable seedling, root, physiological and yield-associated traits, HSAL 428, HSAL 412, G-230, G-61, G-72 and G-203 were identified as promising genotypes. Among these, HSAL 428 recorded the highest grain yield (29.52 g plant -1

), while G-230 combined high grain yield with 100% germination and high seedling vigour; G-72 exhibited high stomatal conductance along with high grain yield; and G-61 showed a favourable combination of yield components and physiological performance. Overall, the findings indicate that an integrated selection approach combining early establishment traits, root characteristics and physiological attributes can facilitate the identification of rice genotypes with potential suitability for dry DSR. The identified promising genotypes constitute valuable genetic material for further breeding and physiological studies aimed at improving DSR adaptation. Nevertheless, their performance and stability should be validated across multiple seasons, locations and moisture regimes before their suitability for dry DSR is confirmed for broader breeding or varietal development.

References

1. Panse VG, Sukhatme PV. Statistical Methods for Agricultural Workers. 4th ed. Indian Council of Agricultural Research, New Delhi; 1985.
2. Anandan A, Mahender A, Sah RP, Bose LK, Subudhi H, Meher J, Reddy JN, Ali J. Non-destructive phenotyping for early seedling vigor in direct-seeded rice. Plant Methods. 2020;16:127.
3. Chauhan BS, Mahajan G, Sardana V, Timsina J, Jat ML. Productivity and sustainability of the rice-wheat cropping system in the Indo-Gangetic Plains of the Indian subcontinent: Problems, opportunities, and strategies. Advances in Agronomy. 2012;117:315-369.
4. Kumar V, Ladha JK. Direct seeding of rice: Recent developments and future research needs. Advances in Agronomy. 2011;111:297-413.
5. Mahender A, Anandan A, Pradhan SK. Early seedling vigour, an imperative trait for direct-seeded rice: An overview on physiomorphological parameters and molecular markers. Planta. 2015;241(5):1027-1050.
6. Negi P, Rane J, Wagh RS, Bhor TJ, Godse DD, Jadhav P, Anilkumar C, Sreekanth D, Reddy KS, Gadakh SR, Boraih KM, Harisha CB, Basavaraj PS. Direct-seeded rice: Genetic improvement of game-changing traits for better adaption. Rice Science. 2024;31(4):417-433.
7. Radford PJ. Growth analysis formulae: Their use and abuse. Crop Science. 1967;7:171-175.
8. How to cite this article: Deshmukh A, Keluskar M, Waghmode B, Mane AV, Kunkerkar R, Gawai M, et al. Phenotyping of rice germplasm for physiological traits suitable for dry direct seeded rice. International Journal of Advanced Biochemistry Research. 2026;SP-10(9):2329-2339. doi: https://www.doi.org/10.33545/26 174693.2026.v10.i9Sac.10171