On the varietal difference of the effect ofshort day-length upon the flower initiation, .its development and the seed ripeningperiod of soy-bean.

Abstract

Experiments were carried out in 1957, to clear up the varietal difference of the effect of short daylength upon the flower initiation and its development, using 7 varieties of soy-bean including the different ecological types, and upon the seed ripening period, using 17 varieties of soy-bean which belong to the different ecological types. The plants were grown in the outdoor and the greenhouse. The half of them were treated with 10 hours day-length. Other half of them were left under natural day-length. The results are summarized as follows : ( I ) The days from cotyledon expansion to flower bud initiation, the days from fiower bud initiation to blooming and the days from blooming to ripening under natural condition show marked differences between varieties of each ecological type, and these days gradually increase following the order I-II-IV-V and the order a-b-c. And, at the same time, the shortening rate of above days by short-day treatment show remarkable differences, and also these rates increase by the same order. These relationships were similarly recognized under natural temperature (in the outdoor) and high temperature (in the greenhouse) . ( 2 ) It was considered that such differences among these ecological types were not due to the differe* nces of day-length and tetnperature in the growing:: period of each variety, but due to the essential differenc of short photoperiodic responses of soybean varieties. ( 3 ) Variety which had a greater shortening rater on days of fiower initiation by short-day tteatement had a greater shortening rate on days of flower development by the saine treatment. Shortening rate on days of blooming became greater in case of continuous treatment during the flower bud initiation and fiower development than in case of each one treatment. Shortening rate on days of flower bud initiation by short-day treatment was alway. larger than shortening rate on days of flower development and on days of seed ripening, but therer was no relationship between shortening rate on days of flower development and shortening rate on; days of seed ripening. ( 4 ) Such relationships between varieties of these ecological types are the results of only one expression under the given day-length and temperature condition in this experiment. So, it will be necessary to study furthermore under various conditions