Enhancing the selection of drought tolerance varieties of rice (Oryza sativa) using germination and early plant growth stress indices

BACKGROUND: Rice (Oryza sativa L.) is a critical staple crop whose productivity is increasingly threatened by drought. However, breeding approaches that identify stable stress tolerance remain limited, particularly regarding the relationship between early-stage performance and subsequent plant growth. This study addressed this gap by evaluating six rice varieties under drought stress at both germination and seedling stages. METHODS: Six rice varieties (SARO, IRRI 18, IRRI 17, SADASHAAME, AHMADA, and SUPA BC) were evaluated for their tolerance under four induced drought stress levels (4, 6, 8, and 12 g/L D-mannitol). A factorial experiment at the germination stage was conducted in a complete block design, while a randomized complete block design was used at the seedling stage. Growth data, relative performance index (RPI), and tolerance index (TOL) were recorded and analyzed using MultCompView, and ggplot2 packages in RStudio. RESULTS: Significant effects were observed between stress level and variety (p < 0.05). The sensitivity of physiological traits to stress across varieties was stage-specific. At the germination stage, SARO (97%) and IRRI 18 (86.67%) recorded the highest germination percentages, while SUPA BC recorded the lowest (22.33%). At the seedling stage, SADASHAAME had the highest plant height (36.20 cm) and dry weight (0.052 g), while SARO had the highest TOL (0.92). Physiological trait performance was reduced significantly under increasing stress, with the highest stress level (12 g/L) resulting in the lowest RPI (72.20) and TOL (0.40). Principal component analysis revealed that PC1 explained 36.0% (germination) and 34.7% (seedling) of variance, with TOL consistently loading positively under high stress across both stages. Cluster analysis showed stable grouping for varieties across stages. Variety tolerance followed the order SADASHAAME ≥ SARO ≥ IRRI 18 ≥ IRRI 17 ≥ AHMADA ≥ SUPA BC. CONCLUSION: The study highlights the complex interactions among rice variety, stress level, and plant growth stage. Variety response to osmotic stress depends on plant growth stage and variety type. Screening at germination alone does not reliably predict seedling performance. Primary selection should be conducted under high stress level with stage-specific performance traits. Molecular characterization and multi-stage plant assessment (including reproductive stages) are recommended for future research.