GENETIC VARIATION AND GEOGRAPHIC CLINE OF ESTERASE ISOZYMES IN NATIVE RICE VARIETIES

Isozyme polymorphism of esterase in Oryza sativa L. was investigated with leaves of 776 native varieties collected from known sites of Asian countries by the use of horizontal agar gel thin layer electrophoresis.The esterase isozymes occurred in altogether fourteen all anodic bands. Of them, nine bands (1A, 2A, 6A, 7A, 10A, 11A, 12A, 13A, 14A) were easily distinguishable and their combination composed 27 different zymograms, indicating the presence of substantially complex variation. Each isozyme differed in its frequency of occurrence in each of the eight areas extended from Sri Lanka to Japan. The bands were grouped into two; one such as 1A and 11A occurred commonly through the areas, the other such as 6A, 7A, 12A and 13A occurred in a distinctive geographic cline.Zymogram patterns comprising the latter group's bands demonstrated a very conspicuous and sequential geographic cline, terminating in very simple zymograms at both south-and north-most areas of Asia. On the contrary, an area including Nepal, Bhutan, Assam, Burma, Vietnam and Yunnan of China was widest in variation of the zymogram patterns. Consequently, this area was postulated to be the center of genetic diversity in esterase isozymes of O. sativa, proposing an important working hypothesis in advancing researches on its speciation and migration.