|CERES No. 134 (FAO Ceres, 1992, 50 p.)|
Asian scientists are pooling their resources by forming consortia to search for ways to increase rice yields and make better use of their region's most important food staple:
"We are following the example of the private sector", says the Philippines-based International Rice Research Institute (IRRI), which broached the idea of strengthening partnerships between national agricultural research systems (NARS) to achieve less costly, more widely applicable results.
The first two consortia formed as a result of IRRI's initiative will focus their efforts on upland rice and rain-fed lowland rice - both cultivated in areas threatened by serious ecological degradation. The partnerships' founding members are Bangladesh, India, Indonesia, the Philippines, Sri Lanka and Thailand. IRRI will contribute expertise, training and facilities, and the Asian Development Bank will provide seed money for a two-year trial period. More than 2.5 billion people worldwide eat rice, and for many of them it is a staple. The world's rice fields cover some 145 million hectares, with an output of about 520 million tons of paddy a year. But, because in many rice-producing countries population pressure limits the land available for rice-growing, it is vital to boost yields as much as possible without increasing the cultivated area.
China, the first country to try to market hybrid rice, has made significant recent progress in increasing yields, using a seed-producing technique that involves crossing a cytoplasmic sterile male variety with another, called a restorer. The resulting heterosis (hybrid vigor) has produced 20 per cent, or one ton per ha, more rice than do other high-yielding varieties.
Forty per cent of China's rice fields grow hybrids, but until
recently, production involved three steps: selecting male sterile lines,
maintaining their sterility and then restoring fertility. But this "three-line"
method requires up to seven stages of backcrossing, making rapid seed production
difficult. It is unsuitable for short-term projects.
In 1986, promising technical innovations and a new source of male sterility based on photo and thermosensitive genie male sterility were presented to the First International Rice Conference held in Changsa, China. A Chinese researcher in Hubei Province discovered a variety in 1973 in which male sterility increased in proportion to the length of the day. As the photosensitive period diminished, fertility was restored. The find made it possible to eliminate the phase of maintaining male sterility, which came about naturally.
Japanese scientists also made an important discovery, finding a new source of male sterility in thermo-sensitivity. They observed that total pollen sterility occurs when temperatures exceed 26 to 28 degrees Celsius, but that fertility is restored at lower temperatures. This made it possible to simplify production of hybrid seed because, again, the number of lines could be reduced to two.
While these discoveries led to a much faster and more efficient seed production method for hybrid rice, the introduction of wide compatibility genes between the indica and japonica varieties has contributed to the elimination of sterility among rice subspecies and increasing the level of heterosis.
The two-line method of producing the second generation version of "miracle variety" hybrid rice, as opposed to the earlier IR8 variety of "miracle rice" employed during the Green Revolution, could reduce the present production cost of hybrid seed by about 50 per cent. Thanks to the high hybrid vigor achieved by crossing between the japonica and the indica varieties, the presence of wide compatibility genes would assure yields 47 per cent greater than those of a hybrid variety widely popularized under the name of V20A/ IR26.
Projects under way
There is now talk of extending this technology, presently applied only in China, to other Asian countries and Latin America. The FAO is implementing projects to develop hybrid rice seed production based on the two-line method in India, Vietnam, Colombia and Brazil. The Indian project is already operational with a US$1.6 million contribution from FAO.
The Chinese have also developed a two-line method using Vary lava, a variety of rice found in Madagascar. This method could be introduced first to Malagasy rice farmers, then to farmers in other African countries who cultivate similar types of rice.
Chinese experts say it will take another five to 10 years to refine the two-line method so it can replace the three-line method. By then, yields may have reached much higher levels - solving at least part of the food security problems of rice-consuming developing countries, and making some rice-growing areas available for other major food crops such as roots and tubers, pulses, cereals and vegetables.