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Varietal technologies of new yield threshold
Since the introduction of dwarf high yielding varieties, breeding emphasis has been to sustain the yield gain achieved by progressively improving them with ability to defend themselves against yield destabilizing factors, especially biotic stresses exploiting hostplant resistance. While breeders have succeeded in sustaining the potential of the semidwarf high yielding varieties, progress in enhancing their genetic yield level, further remained disappointing until Chinese breeders succeeded in breaching the genetic yield level of the dwarf through development of commercially feasible hybrid rice technology by late 1970s. The hybrids with about one ton yield advantage over the best varieties, motivated Chinese farmers to plant them extensively to cover over 55% (18 mill.ha) of China’s rice area by mid 1980s and thereby increase rice production by 20 million tonnes annually. Today hybrids are planted over 85% of the rice area there.
Convinced of the potential of the hybrid technology and impressed with China’s success story, India revived its earlier abandoned interest to replicate China’s example in 1990 by augmenting hybrid rice research in a network mode supported by the ICAR, the FAO-World Bank and Mahyco. Taking advantage of parental lines ideally adapted to India’s tropical conditions and the experience of China in hybrid breeding, hybrid seed production and hybrid cultivation, India could succeed in the next five years with the release of the first generation hybrids with one ton yield advantage. The achievement earned for India, the distinction of being the second country after China to exploit hybrid rice technology on a commercial scale. With the active involvement right from the beginning, of the private sector seed industry the country could evolve and release as many as 50 hybrids in all maturity groups and grain quality. Their impact sadly, could not however, be felt, because of their disappointingly slow pace of adoption. In 15 year period since its advent, the technology could not cross as yet two million hectares as against the pace at which the technology with similar yield edge could spread to over 18 million hectares in China. The reasons for so slow adoption are its inconsistency in yield performance, less acceptable cooking quality, lack of hybrids of medium late maturity required for over 80% of the area in the wet season and susceptibility to all major pests. Rightly diagnosing the factors constraining wide adoption, many new generation hybrids freed from the deficiencies are now in the pipeline. Their release soon can be hoped to accelerate the pace of adoption of this potential technology in irrigated, mainly irrigated and favourable rainfed shallow lowland ecologies and cover as large as 8 to 10 million hectares by 2015 and thereby add 7-10 million tonnes to the country’s rice production. Simultaneously, breeders have been engaged in designing morph-physiologically still more productive new plant type genotypes encouraged by the recent reports from China of varieties in new plant type background capable of yielding close to three fourths of the theoretical yield of 20 t/ha. The new plant type based on the concept of marriage between genotype and crop geometry is characterized by enhanced biomass with no change in the already increased harvest index (45%) and robust root system.
In the development of such super yielding varieties and hybrids, use of subspecific genepools has been found rewarding. Yet another ambitious programme conceived and being launched jointly by the Melinda-Bill Gates Foundation, China and IRRI is Green Super Rice (GSR). The project aims at evolving super yielders combined with high use efficiency of water and nutrients, broad spectrum resistance to all major pests, enriched nutritive quality and adaptation to adverse effects of climate change in varietal and hybrid backgrounds. Several GSR lines now in advanced stages of development, intensive testing and extensive onfarm evaluation in several Asian countries are expected soon to be ready for commercial planting. The GSR germplasm has helped broaden the genetic base for many traits of value enabling countries in the region including India to access and use it along with its own to evolve future varieties of high input use efficiency in the backgrounds of progressively raised genetic yield ceilings.