Longer mesocotyl contributes to quick seedling establishment, improved root anchorage, and early vigor of deep-sown rice

•Farmers’ mean seeding depth under DDSR in rainfed lowlands ranges from 16 to 35 mm.•Seedling emergence from 85 mm was >80% in tolerant cultivars, but <1% in popular cultivars.•Deep-sowing tolerance in the field was attributable to the mesocotyl’s elongation.•Deep-sowing tolerance will be required to improve seedling establishment.