research, 27) a 3% annual increase in rice yield in the long term is very difficult.
How are such new technologies as bio-technology and hybrid varieties appraised for increasing grains yield? Since the appearance of hybrids corn in America in the thirties, the Fl vigor has been considered the break-through technology which would be the best means of increasing yields. But those views are too optimistic. Hybrid rice varieties have been planted principally in China (55% of the countrie's harvested area in 1992), because the high cost of hybrid seed production has been mitigated by cheap labor costs and the government subsidies, and it is said that the rice yield has only increased by 20%. Although the efforts have been made for the last twenty five years, hybrid wheat seeds haven't been successful due to the prohibitively high cost of seed production. 28) Although a significant increase in crop yield has been expected by using bio-technology utilizing gene transformation and gene mapping, virtually no useful result considerably increasing crop yield has been achieved so far. Many researchers understand that it takes several decades to extend new seeds developed by bio-technology among the majority of the farmers in the developing countries. Bio-technology is considered as an important means for genetic research, and it is recognized to bring graduate increase rather than bringing a brake through in yield. 29) IRRI in the Philippines plans to increase yield by 30% through developing 'the super rice' using bio-technology which has the plant type with 90 cm height of four or five short and strong stalks with big ears and eliminating stalks with no ears. 30) However, it is said that this has not been achieved according to Professor Hone of Kyoto University who has heard of the experiments with this rice in Japan.
4. Demand Factors
According to the estimates of the United Nations, population explosion which has occurred mainly in the developing countries after the war, will maintain the peak level during the period of 1990 to 2020. Population increases
