Abstract
In rice, gene pollution may occur when genes that control undesirable characteristics are integrated by natural hybridization. These genes are spread out when the seeds fertilized with alien pollen are used as seeds for the next generation, or when they fall oft the mother plant before the harvest and grow as weeds in the field. Once gene pollution has been spread by farmers', all the products harvested from the polluted fields lose their commer-cial value. Moreover, seeds kept for sowing the next generation must be replaced by new ones. Thus the financial damage is serious. As weedy offtypes that fall down in a field invade neighbouring fields, the pollution spreads more extensively. In fact, red rice cultivars, which have been the most harmful weeds in paddy and upland rice fields in parts of Japan frequently pollute ordinary rice varieties and create significant damage in the farms. The spread of gene pollution can be controlled by preventing either natural hybridization or the multiplication of seeds having undesirable genes. Gene pollution will not spread if the hybrid plants that integrate the undesirable genes do not produce progeny seeds. When new cultivars of rice are rised, the prevention of the spread of gene pollution should become a breeding objective. To prevent it, F1 weakness or F1 lethal genes could be used in such a breeding program.
