Relationship between coleoptile and mesocotyl elongation of upland rice (Oryza sativa L.) seedlings under submergence and soil-sand culture

In rice, the coleoptile and mesocotyl are two morphologically important structures for seedling emergence. After germination, coleoptile and or mesocotyl elongation projects the seedling tip out of the soil and water in which it is planted, allowing the leaves to make contact with the atmosphere thus enabling the seedling to develop into a normal rice plant. Rice genotypes with inherently longer coleoptiles and or mesocotyls are thought to emerge better than those with shorter ones. However, the patterns of elongation under submergence and in soil-sand culture remain unclear especially for upland rice. This study examined coleoptile and mesocotyl elongation in 63 upland rice genotypes comparing elongation patterns under submergence to elongation in soil-sand culture. Coleoptile and mesocotyl elongation in soil-sand culture differed from elongation under submergence. Coleoptile lengths were enhanced more under submergence and mesocotyls grew longer in soil-sand culture. This appeared to link seedling emergence under submergence more to coleoptile elongation, and emergence in drained soil-sand culture largely to mesocotyl elongation. We found no obvious relationship between coleoptile and mesocotyl elongation under submergence. But in soil-sand culture, increases in coleoptile length corresponded to increases in mesocotyl length, suggesting that simultaneously coleoptile and mesocotyl elongation contribute to seedling emergence in drained soils.