Abstract
The present study was carried out to determine the reason for the difficulty in developing common wheat varieties as early as the barley varieties with early maturity. When thirty varieties each of wheat and barley including early and late types were sown outdoors in the fall at Kurashiki, the double ridge stage (T1) of ear primordium differentiation in wheat was markedly retarded compared with that in barley. In spite the lack of difference in the onset of stem elongation (T2) between wheat and barley, in the case of the wheat varieties the time of heading (T3), anthesis (T4) and maturation (M) occurred later than in barley. T1 was most closely related to the heading time in wheat while in barley T2 was. In both wheat and barley, however, T3 was most closely related to M. Differences in the duration of the kernel filling period between wheat and barley were studied using 7 varieties each. Since the wheat varieties always required 3 to 5 days more for kernel filling than those of barley regardless of anthesis time, the accumulated temperature at 9 a.m. during the filling period was 200°C or higher in the wheat varieties than in the barley ones. The results analyzed further with two representative varieties each of wheat and barley indicated that in the barley varieties the rates of increase of the harvest indices were high immediately after anthesis, in contrast to wheat in which the rates of increase were rather low until two or three weeks after anthesis. About the same tendencies were recognized in the rates of increase of 1000 kernel weight in barley and wheat. Furthermore, the straw weight of the barley varieties decreased linearly with the increase in the number of days after anthesis, while in the wheat varieties, the straw weight did not change during the 20 to 30 day period after anthesis. These facts suggest that the differences in the duration of the kernel filling period between the wheat and barley varieties may be due to differences in the translocation of photosynthetic substances from stems and leaves to kernels. This may be the main constraint on the breeding of wheat dultivars as early in maturity as the barley ones.
