Liquid Culturing of Detached Panicles of Rice : Cooled Culture Solutions Extend the Period of Growth

Grain dry-matter increase (GDI) in rice depends highly on assimilate supply from plant parts other than grains. Assimilate supply's contribution to GDI through the panicle organ is often ignored because the net photosynthetic rate in the rice panicle is very low (Tsuno et al., 1975; Ishihara et al., 1990). In order to investigate the effect of nutritional and environmental factors on GDI, it is essential to strictly control the supply of nutrients to grains as well as the panicle environment. If grains on detached panicles cultured under the conditions of controlled nutrient supply and environment grow almost equally as well as those on field-grown plants, we can clarify the factors controlling GDI more easily. As a crossbreeding technique, water culture of detached panicles with leaves attached has been used to harvest set grains (Syakudo, 1958), but it is unknown how rice grains on the panicles cultured in the solution with complete nutrients can grow and what conditions are needed for the detached panicles to achieve GDI similar to that under field conditions. Using the method of liquid culture previously used for wheat (Sing and Jenner, 1983) , we tried culturing· of detached panicles of nee.