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Meeting the challenges – Research & Developmental Strategies
Problems constraining the desired pace of production growth are not without opportunities to overcome them in the era of science-driven agriculture. There are both developmental and technological avenues for achieving the production targeted for 2025 and beyond. While innovative strategies using cutting edge science are underway all over to raise the ceiling to genetic yield, to defend the yield gains against stresses and to enrich the nutritive quality of rice, in this brief exercise, what would help achieve the short and medium term production targets are discussed. Developmental strategies: There are three developmental opportunities to realize the full potential of the currently available semidwarf varieties viz., (a) exploitation of the scope for bringing more area under rice (b) consolidation of the achievable yield of the high yielding varieties/hybrids and (c) intensification of rice cropping. Practically no significant growth in net and gross area has been possible in the last three decades indicative of limited scope for horizontal growth. Yet, opportunities do exist to expand rice area under certain conditions in all the three rice growing continents. In Asia, if rice farming can be made reasonably profitable through appropriate technological interventions, Thailand, Myanmar, Malaysia, Cambodia and Eastern India could offer more area for rice (Hossain, 2004). About, 20 million ha of inland river valley in sourthern and western Africa, of which only 15% are currently cultivated, constitute a potential opportunity for bringing sizeable area under rice cultivation there, (Alexandrotos, 1995). If rice cultivation could provide adequate returns to factors of production to levels comparable with those of other economic activities, Latin American countries such as Brazil, Argentina, Uruguay, Guayana, etc can extend rice cultivation to more area taking advantage of large arable land and irrigation water available (Hossain, 2004). Transformation such of potential opportunities into sustainable production system would require serious research and development effort as well as helpful public policies from the governments concerned. Consolidation of achievable yield by narrowing the yield gap: Plant type based high yielding varieties, although were introduced 45 years back, the full potential of them has not as yet been harvested even in the risk free irrigated ecology, for which they were designed and recommended. Given is seen in large yield differences between rice growing provinces within a country as well as the wide gap exists between achievable yield and what is actually obtained by farmers at district/village levels. The gap is quite wide, the range being between 30-50% in tropical Asian countries without exception. In India, for instance, the yield gap is between 35 and 65% in the rice growing states except the high productive Punjab, Tamil Nadu and Andhra Pradesh, where it is below 30%. Yield gap analysis reveals the gap width to vary with the extent of compliance by famrers to adoption of the recommended package of cultivation practices. More attention to correction of location specific yield depressing factors and motivation of farmers to adopt the recommended package in full would help narrow the yield differences and maximize thereby the productivity level. Integrated Crop Management (ICM), a vastly modified form of the System of Rice Intensification (SRI) is one strategy that would help maximize the harvestable yield by narrowing the gap. It is a site specific package of compatible practices with synergistic benefits designed with twin objectives viz., (a) narrowing the gap between what is being actually harvested at farm level and what is achievable of the modern varieties in a given environment and (b) enhancing the use efficiency of inputs like water, fertilizer, pesticide, etc without compromising on yield. Known by different names such as Integrated Crop and Resource Management in Indonesia, Integrated Rice Crop Management in the Philippines, Rice Check in Australia and Modified SRI in India, the package is now promoted by the FAO in many rice growing countries as ICM since 2004. The package comprises use of right variety and quality seed, low seed rate (10-15 kg/ha) transplanting of young seedlings (12-15 d old) adopting wide space planting (22.5 x 22.5 cm), need based nutrient application, early weeding cum soil stirring, use of organic manure and intermittent irrigation where possible and timely harvest. The package helps to save on seed cost (50%), water use (30%) and fertilizer nutrient (30%). Extensive study in many countries, suggest that adoption of this package would help maximize the yield level of currently used varieties/hybrids by 25-30%. Intensification of Rice Cropping: Taking advantage early and very early maturing, photo insensitive varieties of high per day yield and ability to yield 80-90% of medium maturing varieties like IR8, two rice crops in traditionally single cropped areas and triple cropping in double cropped areas have been tried. In areas, where water and weather are not a limitation, such crop intensification has been found to help raise substantially the productivity/ha/year. The success would, however, depend water availability apart, labour availability favourable weather reasonable labour wage structure and competitive advantage vis a vis non-rice crops in the market. Breeding strategies: Progressive enhancement of genetic yield level placing emphasis on irrigated and relatively favourable rainfed ecologies and defending effectively the yield gains against the still major yield depressing biotic and abiotic factors are central to all strategies contemplated for increasing rice production. The following are some of the short/medium term means to step up the genetic yield level. Raising further the yield level of irrigated rice: Over the last four decades impressive two fold yield increase (2.5 to 5.0 t/ha) achieved of modern varieties has been largely in the irrigated ecology. The rate of increase at around 0.5t/decade on an average is however, not an encouraging trend, as more could have been achieved through varieties in the fertilizer responsive ideal plant type background exploiting the rich variability available in the germplasm. It is believed that not even 15% of the variability available had so far been used. Breeders’ excessive dependance on a very small fraction of the cultivar germplasm and that too restricted to the region specific subspecies viz., indica or japonica for needed variability, is one of the reasons for slow pace of yield enhancement. In the making of the so far released high yielding varieties in any given country, hardly a handful of germplasm is found to have contributed the maximum thus revealing that all our current breeding efforts are on a very narrow genetic base. Massive efforts to broaden the genetic base by involving potential cultivar accessions from all over and the subspecies, especially tropical japonica might help build a bedrock of still large and enriched variability for breeding for progressive enhancement of genetic yield. Raising the genetic yield level of rainfed rice Rainfed ecosystem accounts for about 50% of the global rice area. The complex nature of each of the subecologies under this system largely because of varied water regimes and problematic soils has been the major reason for quite slow growth of production and productivity. The average yield of rainfed rice between 1965-67 and 1995-97 has gone up by hardly 1.4% annually (from 1.45 t to 2.08 t/ha) as against 2.7% (from 3.16 to 5.77 t/ha) of irrigated rice (Hossain, 2004). Precise knowledge now available on the relative prospects of areas characterized as favourable and less favourable in the rainfed upland and lowland ecologies in tropical Asia should provide a base for still more augmented and focussed breeding research in continuation of what has been achieved through IRRI coordinated ecoregional upland and lowland consortia for doing technological justice to the large handicapped ecology bypassed by the Green Revolution. Favourable lowlands and uplands be identified as well in Latin America for further aggressive breeding research to design and develop higher yielding varieties in appropriate plant type backgrounds combining desired level of tolerance to moisture stress and blast disease. Marker assisted breeding/selection could be of value in selectively combining tolerance to abiotic stresses as has been successfully demonstrated recently by IRRI in making the popular lowland variety Swarna tolerant to submergence by introgressing with submergence tolerance gene (Sub1) from the deepwater rice variety FR13A. Similar effort to identify and use one such gene against moisture stress would greatly help defend the inherent potential of many good verieties developed so far for both rainfed upland and lowland ecologies. Extensive adoption of hybrid rice in tropical Asia: Following the development of parental lines well adapted to tropical and subtropical environment, hybrid rice technology has become a reality since 1995 in countries outside China. Unlike, however, in China, where the technology found rapid adoption to cover in 12 years over 15 million ha, the pace of adoption of it outside China has been very slow. It is yet to cover 2 million ha together in the five major countries promotic hybrid rice viz., India, Vietnam, the Philippines, Bangladesh and Indonesia. The major reason for slow spread of hybrids in these countries is their still not satisfactory yield advantage over the best inbred varieties and inconsistent performance, besides less acceptable cooking quality and susceptibility to diseases and insect pests. Serious effort to correct such deficiencies are what is needed to help rapid adoption of the technology in the coming years. The new generation hybrids of intersubspecific new plant type background combining higher yield and yield advantage and more acceptable grain quality now being developed in Vietnam and India are expected to meet such requirements. Being a proven technology with higher yield threshold, taking the hybrid rice technology to 10-15 million ha in Asia alone before 2025 is a distinct possibility, if researchers and policy makers are serious about. Improvement and extensive adoption of super high yield hybrids in China Taking advantage of the fact that intersubspecific (indica/japonica) hybrids express higher yield vigour and understanding the potential of new plant type characterized by higher biomass and efficient root system, China has come up with super high yield hybrids. Capable of yielding 12t/ha, the super hybrids evolved by both 3-and 2-line hybrid breeding approaches and extensively evaluated are expected to replace the relatively less yielding intra-subspecific (indica/indica) hybrids, which occupy now over 60% of its rice area. This development marking the third major yield breakthrough after semidwarf varietal technology and intrasubspecific hybrid rice technology, would greatly help sustain high production growth till and beyond 2025 to cope with the increasing demand. Morphophysiologically more efficient new plant type varieties: It was the change in the plant architecture that helped in the sixties to breach the yield barrier of centuries. Yet, the potential of the dwarf statured varieties was no where near the theoretical yield level of 20t/ha/crop estimated for rice. The productivity level of some of the intersubspecific hybrids approaching closer to such levels convinced rice breeders that genetic yield level of irrigated rice could be raised by another 20-25% through improvement of biomass. The strategy lies in increasing the biomass/unit area by planting less profusely tillering but high panicle weight genotype at high density by manipulating crop geometry. IRRI, China and India have come up with different plant type models but all basically around the concept of marriage of genotype with crop geometry. Among them the model combining the features of the ideotypes of Prof. Yuan and Dr. Khush appears promising, given the potential of an intersubspecific hybrid being experimented with in China. The plant type detailed elsewhere is characterized by semidwarf (~110 cm) stature of very strong stem with top three long and upright leaves, long and heavy panicles with high grain number (>250 grains/panicle), high test grain weight (25 gm/1000 grains), deep and efficient root system, slow senescence and long grain filling period. The new plant type varieties in intersubspecific background already planted over 6 mill. ha in China would help raise appreciably the production and productivity levels while providing a strong base for next breakthrough in yield through the super high yield hybrids now in the advanced stages of development. Improved NERICA for upland and lowland ecologies of Africa New Rice for Africa (NERICA) combining high yield attributes of Asian rice and high adaptability to harsh growing conditions of African cultivar is a boon to lowland and upland ecologies of Africa. Many NERICA lines selected for diverse rice ecologies of Africa yielding double that of the native glaberrima cultivars are extensively evaluated for adoption while some have already been released for commercial planting as detailed elsewhere. The productivity of large wet part of the upland (~70%) ecology in West Africa could be substantially increased by introduction and wide adoption of suitable NERICAs. Though NERICA is a major step forward in evolving high yielding varieties suiting harsh rice ecologies of Africa, there is scope for further improvement of them for still higher and stable yields. A major research effort is what is needed at this juncture to build over the NERICA. While the improved products therefrom would help raise the productivity levels of upland and lowland ecologies, simultaneous efforts to improve the productivity of irrigated rice by accelerated breeding/introduction of progressively better indica, tropical japonica and indica-japonica varieties would herald a sort of productivity-production revolution in this long neglected continent of great potential. Defending the yield gains: Among the yield destabilizing factors across rice ecologies insect pests and diseases constitute the most important. Though sources of resistance are available in large measure for managing many of the pests and minimize the yield losses considerably, there are still some, against which no genetic solution has been found as yet. They include sheath blight, grassy stunt virus-II, stem borer and leaf folder in Asia, Hoja blanca virus and African gallmidge in Africa and continuously emerging new biotypes/pathotypes of increased virulence/viruliferance. The present strategy of developing multipest resistant varieties be strengthened, where hostplant resistance is available, while considering transgenic approach for managing those which continue to defy solution.
FOUR DECADES OF RICE BREEDING – ACHIEVEMENTS, IMPACT, FUTURE DEMANDS AND STRATEGIES -Dr.E.A.Siddiq