Background: Root system architecture (RSA) plays a critical role in drought adaptation by enhancing water and nutrient uptake from deeper soil layers. However, limited genetic variability for root traits in elite rice germplasm constrains breeding progress for drought-prone rainfed ecosystems. Methods: This study characterized 187 EMS-induced mutants derived from the drought-tolerant upland rice cultivar Nagina 22 (N-22) for key root architectural traits under controlled rootstructure conditions during summer 2023 at the University of Agricultural Sciences, Bengaluru. Root length, root volume, root biomass, and total vegetative biomass were measured at 45- 50 days after sowing. Statistical analyses included ANOVA, frequency distribution analysis, Pearson’s correlation, and regression modeling. Results: Significant genetic variability $left( mathrm { p } < 0 . 0 5 right)$ was observed across all traits. Root length ranged from 8.0 to $6 0 . 2 5 ~ mathrm { c m }$ (mean: 17.79 cm), root volume from 2.33 to $7 3 . 3 3 ~ mathrm { c m } ^ { 3 }$ (mean: $1 1 . 4 0 ~ mathrm { c m } ^ { 3 }$ ), and root biomass from 0.09 to 7.01 g plant ¹ (mean: 1.12 g plant ¹). Total vegetative biomass ⁻ ⁻ ranged from 1.28 to 34.89 g plant ¹. Regression analysis revealed strong positive associations ⁻ between vegetative biomass and root volume ( $mathrm { R } ^ { 2 } = 0 . 5 6 4$ , $mathrm { p } < 0 . 0 1$ ), followed by root length $mathrm { R } ^ { 2 } =$ 0.217, $mathrm { p } < 0 . 0 1$ ) and root biomass $mathrm { R } ^ { 2 } = 0 . 1 7 2$ , $mathrm { p } < 0 . 0 5$ ). Root volume showed moderate correlation with root length $mathrm { Delta R } ^ { 2 } = 0 . 2 5 2$ , $mathbf { p } 4 5 mathrm { c m } ^ { 3 }$ . Conclusion: The substantial genetic variability in root architectural traits among EMS-induced N-22 mutants provides valuable pre-breeding material for drought tolerance improvement. Mutants with enhanced root volume and biomass represent promising donors for marker-assisted breeding programs targeting water-mining capacity in aerobic and upland rice production systems.
Background: Root system architecture (RSA) plays a critical role in drought adaptation by enhancing water and nutrient uptake from deeper soil layers. However, limited genetic variability for root traits in elite rice germplasm constrains breeding progress for drought-prone rainfed ecosystems. Methods: This study characterized 187 EMS-induced mutants derived from the drought-tolerant upland rice cultivar Nagina 22 (N-22) for key root architectural traits under controlled root-structure conditions during summer 2023 at the University of Agricultural Sciences, Bengaluru. Root length, root volume, root biomass, and total vegetative biomass were measured at 45- 50 days after sowing. Statistical analyses included ANOVA, frequency distribution analysis, Pearson's correlation, and regression modeling. Results: Significant genetic variability (p < 0.05) was observed across all traits. Root length ranged from 8.0 to 60.25 cm (mean: 17.79 cm), root volume from 2.33 to 73.33 cm³ (mean: 11.40 cm³), and root biomass from 0.09 to 7.01 g plant⁻¹ (mean: 1.12 g plant⁻¹). Total vegetative biomass ranged from 1.28 to 34.89 g plant⁻¹. Regression analysis revealed strong positive associations between vegetative biomass and root volume (R² = 0.564, p < 0.001), followed by root length (R² = 0.217, p < 0.01) and root biomass (R² = 0.172, p < 0.05). Root volume showed moderate correlation with root length (R² = 0.252, p < 0.01). Selected mutants (e.g., MG353, MG382, MG387) exhibited superior root traits compared to wild-type N-22 and checks, with root biomass exceeding 5 g plant⁻¹ and root volume > 45 cm³. Conclusion: The substantial genetic variability in root architectural traits among EMS-induced N-22 mutants provides valuable pre-breeding material for drought tolerance improvement. Mutants with enhanced root volume and biomass represent promising donors for marker-assisted breeding programs targeting water-mining capacity in aerobic and upland rice production systems.