GENETIC AND DEVELOPMENTAL BASES FOR PHENOTYPIC PLASTICITY IN DEEP-WATER RICE

Submergence in water induces drastic changes in the morphology of deepwater or floating rice including a rapid internodal elongation. To study the genetic and developmental bases for its phenotypic plasticity, experiments were carried out using a perennial wild rice accession with deepwater tolerance and a non-deepwater rice cultivar. Selection for deepwater tolerance was performed under 1-m deep water conditions, and backcrosses were made up to the BC5 generation to transfer a gene(s) for deepwater tolerance into the intolerant cultivar. The results indicated that a recessive gene (dw3) was responsible for deepwater tolerance, and plants with dw3 induced internodal elongation in response to submergence. Plants without dw3 showed no internodal elongation and soon died. However, the responsive ability of dw3 was markedly reduced after floral initiation, showing that the induction of internodal elongation was developmentally regulated. Submerged plants with dw3 also showed an increased number of elongated internodes, as well as nodal tillering and nodal rooting, suggesting that changes in relative timing of developmental events due to dw3 induced profound plastic responses in deepwater rice under submerged conditions.