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Development of germplasm with new yield thresholds
In the fourth decade that placed emphasis on further raising the genetic yield level of irrigated rice, possibilities of replicating China’s success story of hybrid rice technology and prospects of developing new plant type varieties were explored. As dealt elsewhere, hybrid breeding research was launched in network mode involving 10 major rice research centres. Taking advantage of the IRRI developed improved male sterile lines like IR 58025A and IR 79156A well adapted to typical tropical conditions, Chinese experience in hybrid breeding and hybrid seed production and active involvement of private sector seed industry the network coordinated by the Directorate of Rice Research, could come up with as many as 50 hybrids in the next 15 years with yield advantage exceeding a ton more than the best inbred varieties and seed production packages capable of giving seed yields of 1.5-2.0 tonnes per hectare. Nevertheless, the pace and extent of adoption of the technology were far from envisaged. Many of the causal factors for the dismal pace of adoption such as inconsistant yield advantage, lack of medium and medium late hybrids required for kharif season in the traditional rice areas, less acceptable grain quality and susceptibility to major pests have now been addressed. Intersub-specific (Indica/tropical Japonica) hybrids of medium late maturity in more productive new plant type background combining acceptable cooking quality and tolerance to some of the pests now in the pipeline are expected to accelerate the pace of adoption of the technology in traditional and non-traditional rice belts and increase thereby its contribution to the envisaged production targets substantially. The new plant type conceived simultaneously as yet another means to raise the genetic ceiling to yield level was based on the long experience and experimental findings of breeders. The strategy lies in increasing the biomass/unit area and hence higher grain yield by planting less profusely tillering but high panicle weight genotypes at high density by manipulation of crop geometry. Indian and IRRI scientists have succeeded considerably in tailoring new plant type varieties and hybrids capable of crossing respectively 12.5 and 14.0 t/ha in the background of inter-subspecific combination. Use of wide compatibility gene loci to overcome the inter-subspecific hybrid sterility and environment genic male sterility supplementing the CMS system for strengthening hybrid breeding has accelerated the development of new plant type based super hybrids and varieties. These developments are hoped to gain increasingly more from hybrid technology.