GRAIN FILLING MECHANISMS IN SPRING WHEAT .5. EVALUATION OF VARIETAL DIFFERENCES IN PLANT-GROWTH AND ASSIMILATE ACCUMULATION WITH GRAIN FILLING PHASES

A regression analysis was conducted on four grain filling phases to ev aluate differences in plant growth and assimilate accumulation in spri ng wheat varieties. Three varieties, early semi-dwarf Haruyutaka bred in Hokhaido Japan, early semi-dwarf Norin 61 bred in Kyushu Japan and late tall Selpek bred in Germany were selected in the present experime nts. Plants were sampled everyday throughout the grain filling period to measure total dry weight, ear dry weight, water soluble carbohydrat e (WSC) in culm and the weight of the culm structure. According to the growth and accumulation pattern, four grain filling phases were deter mined and a regression equation was fitted to each phase. The characte ristics of these varieties are described. Haruyutaka had an intensive growth of culm structure during the initial phase. WSC was kept high u ntil cessation of photosynthesis, then translocated into grain rapidly during the long final phase. Norin 61 had a long early phase with a m oderate rate of WSC accumulation in culm. The grain growth rate was ke pt high even during the final phase. Selpek had the longest duration o f the initial phase but the lowest rate of culm structure growth durin g this phase. The rates of grain growth and WSC accumulation in culm w ere higher during the early phase. This analysis seemed to be helpful to assess the regional grain yield with physiological characteristics of genotype.