Seed priming in dry direct-seeded rice: consequences for emergence, seedling growth and associated metabolic events under drought stress

Drought stress encumbers the seed germination and delays seedling establishment in dry direct-seeded rice. Pot and field studies were carried out to ascertain the role of seed-priming on emergence, seedling growth and associated metabolic events in dry-direct seeded rice system. Seeds of two indica rice cultivars were subjected to different priming agents viz., hydropriming (H2O), potassium nitrate (KNO3; 0.5 %), polyethelene glycol-6000 (PEG; 10 %) and spermidine (Spd; 0.5 mmol L-1). A no-priming treatment was kept as control for comparison. Drought stress was imposed by 15 % PEG solution in a pot experiment; whilst in field trial soil moisture contents were maintained between 15 and 18 %. In pot experiment, drought stress severely hampered the germination rate, seedling growth, and starch metabolism, but increased the antioxidant enzymes activity and lipid peroxidation in both rice cultivars as compared with normal conditions. All the seed priming treatments particularly Spd priming, were effective in alleviating the damaging effects of drought stress under controlled as well as field conditions. In field trial, Spd priming recorded 21, 232, 173, 67 and 78 % higher emergence, shoot length, shoot fresh weight, maximum root length and root fresh weight of dry direct-seeded rice, respectively, compared with control. And such increments were associated with better starch metabolism particularly increased a-amylase activity in primed rice seedlings.