Genetic Interrelationships of Improved Rice Varieties in Asia

摘要

The study of genetic interrelationships of rice varieties in Asia as a part of better understanding crop-destructive insect and disease epidemics of the past is presented. The report shows the genetic diversity of improved rice varieties released in Asia, by analyzing selected crosses made in seven Asian countries. Over a ten-year period, the percentage of semidwarf parents used in the total gene pool nearly doubled because breeders were increasing crosses of semidwarf parents with other semidwarf varieties. Taichung Native I and IR8 were the most extensively used gene sources in 1965-67 but found to drop off to nearly zero in the next ten years. The study shows the use of other International Rice Research Institute semidwarfs increased significantly but the strongest trend was the use of locally developed semidwarf, up from two percent to 49 percent in 1974-75. It is concluded that cytoplasmic similarity of modern varieties, while posing no immediate problem, is sufficiently relevant for prompt broadening of maternal genetic base of modern rices.