Harvest Index and Grain Weight Decline when Wheat Cultivar 'Haruyutaka' Bred in Hokkaido Grows in the Warm Areas of Western Japan

A wheat cultivar, "Haruyutaka", bred in Hokkaido, was planted and examined at nine cultivation conditions of the four seasons, 1995/1996 to 1998/1999, in Yamaguchi, Japan, for the purpose of introducing a new genotype into this area. Another wheat cultivar, "Daichinominori", bred in Kyushu, a part of western Japan in the same area as Yamaguchi, was compared with Haruyutaka. The Haruyutaka cultivar had lower grain yields than Daichinominori did for almost all conditions because it always had a lower harvest index and a smaller 1, 000 grain weight. Haruyutaka's culm had a higher content of water soluble carbohydrate at anthesis than at the milk-ripe stage. This suggested that Haruyutaka had accumulated no reserve material in culm during the former grain-filling period. Showing a larger total dry weight, Haruyutaka increased its grain weight, harvest index, and grain yield as it increased its sink capacity. Daichinominori increased its harvest index as it increased its source ability during the grain-filling period. Haruyutaka seemed to achieve a higher grain yield, a higher harvest index, and a heavier 1, 000 grain yield as a result of photosynthesis activity that was not high, but of a quick remobilization of reserve material in culm to grain under the environment of western Japan.