Beyond Water Deficit: PEG-Induced Osmotic Stress Alters Rice Germination and Early Seedling Performance

Abstract

ice ( Oryza sativa L.) is one of the world's most important food crops, yet its productivity is increasingly threatened by drought stress, particularly during seed germination and early seedling establishment. This study evaluated the effects of polyethylene glycol (PEG 6000)-induced osmotic stress on rice seed germination and early seedling growth under laboratory conditions. Rice seeds were exposed to eight PEG 6000 concentrations (0, 5, 10, 15, 20, 25, 30, and 35% w/v) arranged in a completely randomized design with three biological replicates. Increasing PEG concentration progressively inhibited seed germination and seedling growth. Germination percentage declined from 95% in the control to almost complete inhibition at 35% PEG, while promptness index (PI), germination stress tolerance index (GSTI), vigor index (VI), root and shoot growth indices, and fresh biomass also decreased significantly with increasing PEG concentration. In contrast, the root-to-shoot ratio increased under moderate stress (5–20% PEG) before declining at 25–35% PEG. Pearson correlation analysis revealed a very strong positive association between germination percentage and PI ( r = 0.96), and integrated trait-response analysis demonstrated coordinated reductions in seedling performance under increasing PEG concentrations. These findings indicate that PEG 6000 effectively simulates drought stress during rice germination and provides a practical laboratory approach for evaluating drought tolerance at the early seedling stage