A genealogical consideration on the transition of leading paddy feld rice varieties in Japan during 1908 to 1955

Abstract

For the establishment of the introduction plan for genetic stocks of rice in Japan, the authors compiled the informations and prepared the genealogical map of leading paddy field rice varieties in Japan. This map shows the tendency that the relationship among leading paddy field rice varieties has become closer and their gene sources have become narrower. The influence of foreign rice varieties on the parents of leading paddy field rice varieties are scarce, and none of indica varieties can be found. Reasons for these are considered to be as follows ; 1. For a leading variety in Japan it is necessary to show a high level and good balance of so many characters, that it is difficult to breed a new variety by the hybridization of minor ones. Rice breeders are inclined to cross a leading variety to a leading variety or use it at least as one of the parents. 2. Characteristics of foreign rice varietiesespecially in.dica, are different from those of the Japanese ones. Without any very serious breeding objects or very long term breeding process, indica X japonica hybridization program in Japan will not be economical. 3. The capacity for the permanent maintenance of genetic stocks of rice in each breeding organization in Japan is very low, and there is no seed center either. Up to 1954, only 17.8% of varieties introduced from tropical countries were maintained. Seed sto'rage under dry and cold conditions is recommended. 4. Since there is no information service for genetic stocks of rice in Japan, japanese rice breeders select rice varieties solely through their own efforts. These two reasons also may limit and prevent the wide utilization of genetic stocks for hybridization.