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History of Rice Breeding

History of Rice Breeding
22
Jan

Mechanisms of heat tolerance and Breeding strategies

Heat tolerance is defined as the ability of the plant to grow and produce economic yield under high temperature (Wahid et al., 2007). Tolerance to heat comprises of escape or avoidance mechanisms like timing of panicle emergence, spikelet opening during stress period, anther dehiscence. Heat shock proteins are considered to be the stabilizing factors conferring tolerance to heat thereby protection of structural proteins, enzymes and membranes from heat damage is crucial in temperature tolerance. (Maestri et al., 2002). 
 
Plant architecture is an important trait for tolerance to temperature stress. As an example in some genotypes the panicle is surrounded by many leaves the plant will be able to withstand high temperature stress due to increased transpirational cooling and prevention of evaporation from anther due to shading of leaves. The early morning flowering of rice plant is a useful phenomenon imparting heat tolerance to rice plant. These traits can easily be used in breeding programmes as it inherits in simple manner (Yoshida, 1981). Genotypes of Oryza glaberrima flower much earlier in the day with more than 90% of the spikelets reaching anthesis by 09.00 h. (Prasad et al., 2006). This trait can be used for introgression in O. sativa genotypes. It has been reported that cultivars with large anthers are tolerant to high temperatures at the flowering stage. (Matsui and Omasa, 2002). 
 
For high temperature tolerance, traits such as spikelet fertility can be used as a screening tool during the reproductive stage. Selection of heat tolerance should be done for those materials which can tolerate temperatures higher than 38oC. Cultivars such as N22 has already been identified as high-temperature tolerant so these material can be used in breeding programmes as donors. Genetic modification of the male reproductive organs should be emphasized as it is more sensitive to high temperature. Candidates genes can be identified using QTL mapping, by studying the association of the phenotype and its associated markers.  Identification and breeding of heat tolerant germplasm should be carried out for exploiting variation both in genotypic and morphological characters. 

       Table1: Symptoms of heat stress in rice



Growth stage


Threshold temperature(oC)


Symptoms


Emergence


40


Delay and decrease in emergence


Seedling


35


Poor growth in the seedling


Tillering


32


Reduced tillering and height


Booting


----


Decrease number of pollen grains


Anthesis


33.7


Poor anther dehiscence and sterility


Flowering


35


Floret sterility


Grain formation


34


Yield reduction


Grain ripening


29


Reduced grain filling

 
 
File Courtesy: 
Chandan Kapoor, H. Kalita, R. Gopi, A.K. Mohanty and Pradeep Chettri ICAR Research Complex for NEH Region, Sikkim Centre, Tadong Gangtok TRAINING MANUAL ON RICE KNOWLEDGE MANAGEMENT FOR FOOD AND NUTRITIONAL SECURITY (28th Nov. – 04 th Dec., 2013)
21
Jan

Target traits in rice for climate change

Heat tolerance
Most of the rice is currently grown in those areas where the current temperatures are close to optimum. By the end of 21st century the rice yields have been estimated to be reduced by 41% (Ceccarelli et al., 2010). It has been evidenced that increase in night temperature has been the main cause of increase in global mean temperature resulting in decrease yields (Peng et al., 2004 and Sheehy et al., 2005).
 
Effect of high temperature on rice plant
The optimum temperature for the normal rice development ranges from 27 to 32oC (Yin et al., 1996). Flowering and the booting stage in rice is considered to be most susceptible to temperature. Temperature higher than the optimum induced floret sterility and decreased rice yield (Nakagawa et al., 2003). High temperature causes floret sterility and decreased ability of pollen grains to swell, resulting in poor pollen dehiscence. Temperature increase of 1oC shortened the number of days from sowing to heading in some genotypes. The symptoms of heat stress in rice has been shown in Table 1.
 
Mechanisms of heat tolerance and Breeding strategies
Heat tolerance is defined as the ability of the plant to grow and produce economic yield under high temperature (Wahid et al., 2007). Tolerance to heat comprises of escape or avoidance mechanisms like timing of panicle emergence, spikelet opening during stress period, anther dehiscence. Heat shock proteins are considered to be the stabilizing factors conferring tolerance to heat thereby protection of structural proteins, enzymes and membranes from heat damage is crucial in temperature tolerance. (Maestri et al., 2002).
Plant architecture is an important trait for tolerance to temperature stress. As an example in some genotypes the panicle is surrounded by many leaves the plant will be able to withstand high temperature stress due to increased transpirational cooling and prevention of evaporation from anther due to shading of leaves. The early morning flowering of rice plant is a useful phenomenon imparting heat tolerance to rice plant. These traits can easily be used in breeding programmes as it inherits in simple manner (Yoshida, 1981). Genotypes of Oryza glaberrima flower much earlier in the day with more than 90% of the spikelets reaching anthesis by 09.00 h. (Prasad et al., 2006). This trait can be used for introgression in O. sativa genotypes. It has been reported that cultivars with large anthers are tolerant to high temperatures at the flowering stage. (Matsui and Omasa, 2002).
For high temperature tolerance, traits such as spikelet fertility can be used as a screening tool during the reproductive stage. Selection of heat tolerance should be done for those materials which can tolerate temperatures higher than 38oC. Cultivars such as N22 has already been identified as high-temperature tolerant so these material can be used in breeding programmes as donors. Genetic modification of the male reproductive organs should be emphasized as it is more sensitive to high temperature. Candidates genes can be identified using QTL mapping, by studying the association of the phenotype and its associated markers.  Identification and breeding of heat tolerant germplasm should be carried out for exploiting variation both in genotypic and morphological characters. 
  •  
File Courtesy: 
Chandan Kapoor, H. Kalita, R. Gopi, A.K. Mohanty and Pradeep Chettri ICAR Research Complex for NEH Region, Sikkim Centre, Tadong Gangtok TRAINING MANUAL ON RICE KNOWLEDGE MANAGEMENT FOR FOOD AND NUTRITIONAL SECURITY, ICAR-NEH (Nov,28th –Dec, 04th 2013)
21
Jan

Breeding Strategies For Development of Climate Resilient Varieties In Rice

Climate change has been a hot topic nowadays and its impact on agriculture and related fields makes the scientific community to work towards innovating new technologies which proves resilient during fluctuations in climate. In a report by IPCC (2001) which states that in the past century the temperature have increased by more than 0.6oC. It is very surprising to know that most of the warming has occurred since the 1970s and also the warmest years has occurred in the past decade. Further, looking at the last 1000 years, the most warmest years have occurred in the last 60 years and this has caused rise in the occurrence of floods and drought (Wassmann and Dobermann, 2007). 
 
As a C3 plant the rise in Co2 concentration will have beneficial effect on rice plant but the overall effect in the tropical areas will be negative. Erratic rainfall and extreme weather events will increase frequencies of both drought and floods. Higher temperature affect the rice crop particularly during the pollination stage which results in more sterile grains and thus less yield. Increase in sea level will cause inundation of more coastal areas and increase in salinity problem of the coastal areas. Change in climate will have effect on insect pest and diseases. Some of the pathogen and insect pest may proliferate and cause epidemics in rice. Drought and floods will cause change in water use efficiency and nutrient use efficiency of the crop and also the nutrient uptake of the rice due to change in the soil microclimate. Rice crop suffers from a number of stresses which hamper the rice production directly or indirectly. Stresses like drought, cold, heat, disease/insect and flooding affects the rice crop economically. It is estimated that the frequency of these stress environment will increase in the near future.
 
Plant breeding technologies often combine traditional knowledge with cutting edge biotechnological techniques are already making real impact in meting the challenge of climate change. Apart from crop management strategies for climate change Plant Breeding plays a major role in combating this change by evolving such genotypes which can withstand in stress environments. Breeding climate resilient varieties is a comprehensive approach for mitigating the effects of climate change on rice.

The integration of conventional breeding techniques with modern biotechnological approaches which covers the genomics, proteomics and phenomics aspects of the crops makes the breeding process more efficient and evolving the new rice varieties in much shorter time. Genetic resources are a store house for alleles that provide resilience to the crop under various stresses. The traditional cultivars are valuable germplasm which can be used in breeding programmes.  MAS for climate resilient traits in rice have proved to be effective in varietal development. QTL mapping for genes conferring resistance to various stresses in rice is quite effective methodology for mapping genes and its introgression in elite varieties. Here we discuss various stresses in rice due to climate change and the breeding strategies for mitigating the stress and development of varieties which will be the future weapon to cope with climate change.

 
File Courtesy: 
Chandan Kapoor, H. Kalita, R. Gopi, A.K. Mohanty and Pradeep Chettri ICAR Research Complex for NEH Region, Sikkim Centre, Tadong Gangtok, TRAINING MANUAL ON RICE KNOWLEDGE MANAGEMENT FOR FOOD AND NUTRITIONAL SECURITY, ICAR-NEH (Nov,28th –Dec, 04th 2013)
13
Jul

Future demands and challenges ahead

                   About one billion plus of the global population still remain undernourished, inspite of the claims of grain revolution and plenty. Over 60% of them and majority of the still growing number are from Asia, where rice is the food and livelihood. Whatever may be the reason for this situation, the bottomline of all our current and future efforts should be for ensuring physical and economic access to rice-enough and for all in the rice world. Precise estimation of future needs keeping in view the population growth and income level dependant consumption of rice is important for effective planning to achieve such a goal. Demand projection computed using IFPRI developed IMPACT model (Rosegrant et al., 1995; Hossain 1998) at an annual growth rate of 1.02% is 417 million tonnes of milled rice by 2025. At the current rates of population growth and increased percapita consumption in the low income developing countries (Table 58) however, the demand would be close to 550 million tonnes of milled rice (822 million tonnes of rough rice) in 20 years from now, which amounts to about 27% increase (118 million tonnes) over the present production level of 430 million tonnes (642 million tonnes of rough rice) (Table 59). At the actually required production growth rates of 1.46, 1.26, 0.58%, the estimated demand of South Asia, South East Asia, and East Asia would be respectively 161.7 (27.8% more), 117.1 (2% more) and 158.2 (60% more) million tonnes of milled rice (Table 59). Some of the major rice growing countries in the region that are expected to grow rapidly in their rice demand by 2025 according to IRRI economists are The Philippines (65%), Malaysia (56%), Bangladesh (51%), India (46%), Vietnam (45%), Myanmar (42%) and Indonesia (38%). This would require quite steep vertical yield growth in the face of limited scope for horizontal growth. The yield level will have to be raised by 22.8, 16.0 and 2.1% over the current yield level of 2.19, 4.18, 2.6 t/ha respectively in South Asia, East Asia and South East Asia. Achievement of such a high target is not going to be an easy task, given the rapidly declining production-productivity growth in these major rice growing subregions of Asia (Table 59) coupled with shrinking favourable growth factors of the 70s and 80s, especially natural resources like irrigation water, arable land and access to needed genetic variability. Deteriorating soil quality and productivity, large rainfed area (>50%) both in Asia and Africa suffering from drought, submergence and problematic soils with no major yield breakthrough as yet, increasingly complex pest scenario with continuously emerging new and more virulent/viruliferous biotypes/pathotypes and above all rice farming becoming increasingly unattractive to the grower because of rapidly declining farm return would make the task of meeting the future production targets much more difficult and challenging.

 

Table 58: Changes in rice consumption, selected Asian countries

Table 59: Projection of demand, production and net trade of rice by region (in million tonnes of milled rice)

*-% increase to be recorded to reach the projected production by 2025

#-by keeping area under rice at the level of 2006

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FOUR DECADES OF RICE BREEDING – ACHIEVEMENTS, IMPACT, FUTURE DEMANDS AND STRATEGIES -Dr.E.A.Siddiq
13
Jul

Breeding semi dwarf japonica varieties

Ever since the introduction of short statured varieties that enabled tropical Asia witness a major yield breakthrough in indica rice, there has been serious efforts to replicate the strategy in the japonica growing temperate and semi temperate countries like Korea, Japan, USA, etc. The dwarfing gene (sd1) in the donor variety Dee geo wu gen could not however, be exploited for development of similar plant type in japonica rice, because of the constraint of intersubspecific hybrid sterility. Breeding strategy to overcome the indica/japonica hybrid sterility barrier, if to use the DGWG source or finding compatible alternate dwarfing gene source are the two options for developing semidwarf statured high yielding japonica varieties. South Korea was the first to successfully recombine the DGWG dwarfing gene in japonica background by crossing the japonica variety Yukara with T(N)1. To overcome F1 spikelet sterility and combine all other desirable characteristics, the F1 was backcrossed with the semidwarf indica variety IR8. Of many derivatives obtained therefrom, the line Suweon213 (IR667) was named ‘Tongil’ in 1971 and released in 1972. Despite its impressive plant type and yield potential, its grain quality was less acceptable to Korean consumers, who are used to the quality of traditional japonica varieties. Also, its level of resistance to rice blast, bacterial blight brown planthopper and low temperature conditions was far less than desired. Also, it was not suitable for late season planting. Nevertheless, Tongil varieties proved good ‘bridge parents’ for progressively improving the productivity quality and adaptation to the stresses (Fig 9). Among the bridge parents Iri317 (Jinhaung/IR2622) proved to be the best combiner. Intensive breeding using such parents with the objective of correcting the deficiencies resulted in 18 Tongil type varieties between 1974 and 1979 and almost as many were released between 1979 and 1989. Some of the best varieties among them included Milyang30, Suweon284, Milyang 42, Iri338, etc. The breeders’ success in recombining the desired quality and cold tolerance is attributed to their strategy of backcrossing or top-crossing with indica parent as against the earlier Japanese practice of backcrossing with japonica parents. Korean breeders have been preferring always to use genotypes of Tongil plant type as one of the parents to improve rice varieties in view of their excellent morpho-physiological frame.

Fig Bridge improvement from japonica-indica crosses

               As for the adoption of Tongil varieties, despite the improvement made, less than acceptable cooking quality, declining yield advantage over the traditional japonica varieities, relatively low price offered in the market, and no respite from pests have together contributed to the decline of area under Tongil varieties. Further improvements being effected on yield and quality, diversification of the varieties and government support are expected Tongils to continue to contribute immensely to the country’s future production goals. In evolving higher yielding semidwarf varieties, Japan and the USA also faced the same problem of indica-japonica hybrid sterility when attempted to take advantage of DGWG gene. Limited progress in recombining the DGWG gene with popular tall/semi tall japonica varieties necessitated search for dwarfness donors in japonica genepool itself. In Japan, identification of three different dwarfing gene sources of spontaneous and induced origin enabled enhancement of productivity of temperate japonica varieties. By crossing of Jikokku, a native dwarf with Zensho26 several high yielding varieties like Hoyoku, Kokumasari, Shiranui, Reihou, Nishihomare, Minaminishiki, etc were developed for southern China. Many more high yielding varieties have been developed subsequently through hybridization of them with other varieties (Fig 10). The variety Reimei widely cultivated in north China in the 70s is a gamma radiation induced dwarf mutant isolated from the variety Fujiminori. Using Reimei as the dwarding gene source with Toyanizhiki, the popular variety Akihikari was developed. It ranked fourth in area coverage, by occupying over 1,20,000 ha in 1979. Another high yielding dwarf variety Kochihibiki released in Central Japan is a product of the cross involving Shiro Senbon, a local dwarf of spontaneous origin (Kichuchi, 1986).

                          High yielding varieties developed using spontaneous and induced dwarf mutants in temperate Japonica resistance to lodging, responsiveness to fertilizer and grain quality to US market standards. Varietal improvement, in keeping with the market preference, has been for development and sustenance of short and medium grain type temperate japonicas and indica – like long grain type tropical japonicas (earlier believed to be of indica-japonica origin) respectively of low and intermediate amylose content. The breeding trend continued until 60s, when semidwarf indica varieties marked a major yield breakthrough in tropical Asia. Rice improvement strategy since then progressed from complete reliance on japonica germplasm to backcrossing of single genes from indicas into japonica and increasingly of improved cultivars from indica by japonica crossing (Rutger, 2004). To evolve semidwarf varieties of high yield potential without compromising on japonica grain quality, a breeding strategy using two different dwarfing gene sources has been adopted. Beginning in the late 60s, breeders started introgressing semidwarfness successfully from the widely used DGWG of the indica source through backcrossing to local quality germplasm. Two significant achievements of this breeding strategy have been M9, the popular semidwarf cultivar developed from the cross of IR8 with California quality germplasm (Carnahan et al., 1978) and Lemont developed of crosses involving Blubelle/T(N)1 derived semidwarf varieties as dwarfing source and traditional long grain varieties of southern US (Bollich et al., 1985). Whereas M9 served as the parental source for the development of many semidwarf cultivars (Mackill and McKensic, 2003), Lemont became the ultimate semidwarf donor for several semidwarf quality varieties in the southern U.S. Under the ‘Base-broadening’ programme, many indica varieties that performed far superior to local varieties have been increasingly involved in US rice breeding programme (Rutger, 2004). The other strategy was to use dwarf mutants induced in locally popular varieties as dwarfing gene source. Use of such sources help to overcome the quality problem, while improving the plant type. An example of how such improvement achieved was the induction of the semidwarfing gene sd1 in the cultivar Calrose, which was released as Calrose76, the first semidwarf cultivar in California (Rutger et al., 1977). The mutant cultivar, though not widely grown, served as the potential dwarfing gene source for nine additional California released cultivars (Rutger, 1992). The induced mutation approach was subsequently used to isolate 11 semi dwarf mutants in Arkansas cultivars all non allelic to sd1. Egypt is yet another traditionally japonica rice growing country. Its experiment with long grain indica rice varieties like IR28 from IRRI failed to catch up with farmers as well as consumers despite their higher yield and resistance to blast disease. Keeping the consumer quality central to its breeding efforts, Egypt placing emphasis on earliness for crop intensification, high per day yield and resistance to blast, has come up over the last 20 years, with varieties that raised the productivity to 10t/ha. Significantly, the ruling varieties have in some way involved indica-japonica derivatives and induced dwarf mutant variety of the US as sources of dwarfness. For instance, popular varieties of today such as Giza 178 and Sakha101 and Giza175 have involved respectively Tongil type germplasm like Milyang49, Milyang79 and Giza 175, which involved indica line 1394-10-1 in their development and Giza176 involved Calrose76, an induced dwarf mutant variety of US. Increasingly the country’s rice germplasm is rich enough with sources for resistance to lodging, blast disease and salinity as well as for yield enhancement-all in the background of japonica grain quality.

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FOUR DECADES OF RICE BREEDING – ACHIEVEMENTS, IMPACT, FUTURE DEMANDS AND STRATEGIES -Dr.E.A.Siddiq
13
Jul

Conclusion

Search for new yield thresholds has been one of the major long term research priorities in rice. After successful development of semidwarf varieties 50 years back and hybrid technology 30 years back in China there has been no sign of yet another breakthrough for long. This has been largely because of breeders’ excessive dependence on the cultivar germplasm for needed variability.

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FOUR DECADES OF RICE BREEDING – ACHIEVEMENTS, IMPACT, FUTURE DEMANDS AND STRATEGIES -Dr.E.A.Siddiq
13
Jul

Process of progressive evolution of modern varieties

The process of evolution of modern varieties underway since 60s has been decisively progressive keeping in view the changing needs and priorities of the stakeholders in the rice sector, especially the grower, the consumer and the trader without, however, compromising on the productive semidwarf and fertilizer responsive plant type. The improvements have been broadly for crop duration to suit different crop seasons and cropping systems, grain quality to meet diverse consumer preferences and tolerance to biotic and abiotic stresses. Also, the successful breeding efforts included raising of the ceiling to yield through exploitation of hybrid vigour in China since late 70s and in a few countries outside China since mid 90s. It was the release of progressively improved varieties in quick succession and pace of replacement of old varieties of declining utility by new ones with distinct economic edge in terms of enhanced yield, higher resistance/tolerance against stresses or better grain quality that sustain high production growth across ecologies, regions and countries. But as some generalize the process of evolution of modern varieties was not in the order of yield, resistance to stresses, quality, etc. The order varied with the country with however, the productive semidwarf plant type remaining common to modern varieties of all generations. Whereas in China, which was taking advantage of short statured varieties since early 60s, the priority has been to breach the yield through hybrid technology, which it developed and started exploiting since late 70s. It is to be followed by super high yield varieties and hybrids, which China is experimenting with since late 90s. Its priority simultaneously has been for shorter duration, better grain quality and broad spectrum resistance to biotic stresses. In the tropical Asian countries outside China like India, breeding emphasis has been in the order of sustaining high yield through semidwarf plant type varieties but of different maturity to suit varied crop growing seasons and fine grain type with acceptable dry and flaky cooking quality till 70s followed overlappingly by resistance against insect pests and diseases from mid 70 onwards and improved plant type with tolerance to location specific abiotic stresses for different rainfed lowland and upland ecologies being continued seriously from early 80s and genetic yield enhancement through exploitation of hybrid vigour since Mid 90s. Likewise all the major rice growing countries in Asia have been engaged overlappingly with different breeding priorities giving due emphasis to high yield, disease insect pest resistance, better grain quality, reduced duration all in the semidwarf plant type background. In japonica rice growing Korea, Japan, Taiwan and northern China in Asia, the USA, Australia, Egypt and Near-east countries, breeding for high yield, milling and cooking qualities and resistance to blast disease has been the priority since beginning, while in O. glaberrima growing West and Central Africa for reasonably high yields and adaptation to moisture stress/problem soil conditions and resistance to pests. Relevance of varieties to a given situation, no matter they are traditional or modern, depends on how long since their release/introduction they remain popular with farmers/consumers. It is not uncommon that some of the of first generation varieties continue to remain popular in as late as fourth or fifth generation. For instance, Mahsuri a semitall, lodging prone variety of the pre-Green Revolution period is popular even after 40 years of its introduction. Same was the case with IR8 and Jaya, which remained popular for over 30 years occupying globally a sizeable area. Such slow pace of varietal replacement is quite common in rainfed and other harsh rice ecologies. For instance, Swarna, a variety found well adapted to rainfed shallow lowlands released in the 70s is still the most sought after variety in India and Bangladesh. But for such exceptions, it is the timely replacement of old varieties by more relevant new varieties that has been sustaining required production-productivity growth.

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FOUR DECADES OF RICE BREEDING – ACHIEVEMENTS, IMPACT, FUTURE DEMANDS AND STRATEGIES -Dr.E.A.Siddiq
13
Jul

Research & developmental strategies

Meeting the challenges – Research & Developmental Strategies 

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FOUR DECADES OF RICE BREEDING – ACHIEVEMENTS, IMPACT, FUTURE DEMANDS AND STRATEGIES -Dr.E.A.Siddiq
13
Jul

Institutes involved in rice improvement

Speedy evolution and extensive adoption of progressively improved varieties/hybrids in the last four decades would not have been possible but for the well organized institutional mechanism for accessing needed genetic variability, tools and techniques for generating breeding material and systems for reliable and rapid evaluation of them and production and supply of quality seed. Establishment of the IRC in 1949 under the FAO framework was the first global initiative for promotion of rice research and development. Since its inception it has been engaged in various rice improvement related research and development programmes. Among several, cooperative varietal testing, collection cateloguing and maintenance of rice cultivar germplasm and Asiawide indica-japonica hybridization for yield enhancement of tropical rice are important. Involved in setting up several regional networks/working groups during the 80s, it has been supporting Interregional Cooperative Research Network on Rice in the Mediterranean Climate Areas, Wetland Development and Management Network/Inland Valley Swamps, Working Groups on Hybrid Rice in Latin America and International Task Force on Hybrid Rice. FAO has MoUs with IRRI for strengthening collaborative action aimed at promoting wider adoption of hybrid rice technology outside China and with WARDA for rainfed rice technology diffusion in West Africa. Under the Rice Development Programme as approved by IRC member countries, FAO and International institutions, have the many programmes such as Hybrid rice development & use, Rice Integrated Crop Management, New Rice for Africa (NERICA), Prospecting with rice and Support to the special programmes on Food Security (Rice Almanac, 2002) The second major institutional support for improvement of rice was the establishment of IRRI with the mandate of improving the well-being of present and future generations of rice farmers and consumers by generating and disseminating rice related knowledge and technology and strengthening the national rice research systems (NRRS). Its problem focused activities vis a vis the mandate broadly cover (a) collection, conservation and evaluation of genes of value, documentation and exchange of germplasm (b) improvement of rice for enhanced productivity, stability and profitability for diverse rice ecologies and (c) facilitating flow of germplasm and knowledge to NARS through International Rice Testing Programme/ecoregional research networking on problems of mutual interest (eg: Rainfed Lowland and Upland Research Consortia Research networks on Hybrid Rice; Asian Rice Biotechnology Network etc and training). Other major institutional initiatives for improvement of rice include establishment of West Africa Rice Development Association (WARDA) in Africa established in 1970 as an autonomous intergovernmental research association of 17 West and central African countries (since 1980, a member of the CGIAR). Is mandated with ensuring food security and allevation of poverty in the region through technology development for sustainable growth of rice sector. Yet another effort for improvement of rice in Africa has been through the International Institute for Tropical Agriculture (IITA) located in Nigeria. The CIAT was established in 1967 in Latin America with the mandate of alleviating hunger and poverty in the tropical developing countries through enhancement of agricultural productivity by developing and applying science and technology. Among its major mandated crops rice has been one since its inception. The rice programme aiming at improving the nutritional and economic well-being of rice growers in Latin America and the Caribbean focuses on germplasm improvement for increasing production/productivity on sustainable basis.

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FOUR DECADES OF RICE BREEDING – ACHIEVEMENTS, IMPACT, FUTURE DEMANDS AND STRATEGIES -Dr.E.A.Siddiq
13
Jul

The era of semi dwarf high yielding varieties

Taichung (Native)1-the first semidwarf indica: Taiwanese breeders had been serious since the World War II to improve the productivity of their very low yielding tall native indica and of the introduced japonica varieties. The breeding strategy has been to reduce plant height to lessen their pronness to lodging, to enhance fertilizer responsiveness and to make them early maturing and photo-thermo insensitive enabling double cropping of rice. The effort of years led to the successful development of Taichung (Native)1, the worlds’ first high yielding semidwarf indica variety. Evolved of the cross involving Dee-geo-wugen, a short statured mutant of spontaneous origin and the popular tall variety Tsai-Yuan-Chung, it is considered rightly to represent a ‘giant stride’ in the global effort to raise the ceiling to genetic yield level in indica rices (Huang et al., 1972). Characterized by semidwarf stature with strong culms and upright foliage, short growth duration with photo-insensitivity, fertilizer responsiveness and non-lodging, T(N)1 yielded more than two times that of the locally popular tall varieties. In a few years since its introduction, over 0.8 million ha were planted to it in tropical Asia (Chander, 1966; Huang et al., 1972).
                                          Introduced in India in 1964, it marked the beginning of the ‘era of yield revolution’ (Chander, 1972; Shastry, 1968). It was reported to have yielded 8.0 and 5.0 t/ha respectively in dry and wet season as against 3.4 and 2.5 t/ha by the local variety Mtu15. Sadly, on account of its high susceptibility to bacterial leaf blight (BLB), blast, Rice Tungro Virus (RTV) and brown planthopper (BPH), its cultivation came to an abrupt end by late sixties. IRRI developed IR8 then started gaining ground all-over by virtue of its higher yield edge over T(N)1 and higher level of tolerance to BLB and BPH. Though T(N)1 could survive only for a short period, it provided the dwarfing gene source and base for development and promotion of plant type based high yielding varieties. Ponlai varieties of improved plant type: Taiwanese breeders simultaneously improved japonica varieties popularly known as ‘Ponlai’ by continuous selection for high yield, short duration and adaptability to both the seasons of subtropical Taiwan. The effort led to the development of a series of high yielding varieties like Taichung65, Chianung242, Tainan-3, Tainan5, Taichung 180, Taichung 186, Hsinchu56, Kaohsiung53 etc. Performing consistently well with yield levels ranging from 6 to 7 t/ha, they were very popular with farmers in many countries outside Taiwan.
                                         Many of them introduced in several Afro-Asian countries including India were found well adapted yielding 5-7 t/ha. For instance, Tainan3, Taichung 65 and Kaohsiung53 introduced in southern states of India, were very successful, because of their high yield potential. Yet, like T(N)1 they too could not be sustained on account of their cooking quality not acceptable to consumers and susceptibility to major pests. The modern varieties that heralded Green Revolution: An important development that accelerated breeding research at global level was the establishment of IRRI in the Philippines in 1960. Breeding activities began the very next year with the primary objective of evolving non-lodging semidwarf varieties with higher yields, led to the development and release of IR8 in 1966. A rare recombinant from the cross between Peta, the popular javanica (tropical japonica) variety of Indonesia and Dee-geo-wugen, the dwarfing gene source from Taiwan, IR8 was the ideal plant type with the highest yield potential the breeders had been dreaming for. The pace at which it was adopted in a short span of time almost in every rice growing continent, provided the momentum for development of a series of high yielding semidwarf varieties at IRRI and NARS.
                                           While serving as an improved plant type donor in place of earlier used T(N)1 and DGWG, IR8 helped breeders develop precise ‘selection eye’ for genotypes of high yield - the panicle number type and high panicle density per unit area. Thousands of crosses of IR8 or its immediate derivatives from crosses with popular tall varieties of the rice world, especially of Asia made at IRRI had led to the evolution and release of a series of high yielding varieties for irrigated ecosystem, which included IR20, IR26, IR28,IR30, IR36, IR42, IR50, IR64, IR72 and IR74 over the years. Simultaneously the rice growing countries in Asia, came up with hundreds of high yielding dwarf varieties, many bred by them and sizeable of IRRI developed varieties/breeding lines. As IRRI has accessed and used germplasm of value from NARS for developing progressively improved varieties, NARS too have used abundantly both basic and improved germplasm of their need from IRRI through the unique global testing network viz., IRTP/INGER that facilitated free and speedy two-way flow of germplasm. Since the advent of the miracle variety IR8, NARS along with IRRI have evolved and released for general cultivation over 4000(?) modern varieties suiting major rice ecologies with emphasis on irrigated production system which accounting for over 55% of the global rice area contributes the maximum to rice production.

 

13
Jul

Breeding prior to plant type varieties

Immediately after the World War II, the major problem the world faced was serious shortages of food. The deficiency ranging between 15 and 20%, especially in the rice dependant Asia, leaving a large population die of undernourishment and malnutrition made the United Nations Organization (UNO) to identify ‘increasing food production by scientific means’ among its priorities. The founding of the Food and Agriculture Organization (FAO) and establishment of the International Rice Commission (IRC) under its framework in 1949 was the major step forward towards this mission. Series of Asiawide research programmes initiated by this institutional mechanism to step up rice production included collection, cataloguing and maintenance of germplasm, Cooperative Varietal Testing, Variety-Fertilizer Interaction and Indica-Japonica Hybridization. Whereas the cooperative multi country evaluation of promising entries from different countries enabled identification and introduction of the best performed in the participating countries, the study of variety x fertilizer interaction in the identification and exploitation of fertilizer responsive genotypes in breeding programmes. The collection and cataloguing of cultivar germplasm into varietal groups and maintenance of indica germplasm at Cuttack in India and Bogor in Indonesia, Japonica at Hiratsuka in Japan and the USA and the floating rices at Habiganj in Pakistan now in Bangladesh proved a valuable and readily accessible source of variability for use by breeders all over. These early initiatives of the FAO/IRC were, in a way the forerunners for the coordinated variety testing programmes of the NARS and the International Rice Testing Programme (IRTP) International Network of Germplasm Evaluation and Utilization of Rice (INGER) of the IRRI since 70s and the International Rice Gene Centre (IRGC) at IRRI respectively.

Early breeding research in tropical Asia began with the improvement of native varieties by ‘pureline selection’, the strategy for purification of highly heterogenous farmer varieties into readily recognizable ones of uniform stature, maturity and grain type. Though the strategy had helped greatly to restrict the number of varieties, it hardly helped raise appreciably the genetic yield level. The rediscovery and elucidation of Gregor Mendel’s Laws of Inheritance, a hundred years back was the defining moment in the history of biology. It was the understanding of the laws of genetics that convinced crop breeders hybridization as the most effective means to generate more variability, on which selection could be practiced in desired direction. Application of this knowledge in rice was however, restricted to improvement of simply inherited traits rather than the genetically complex yield. If pureline selection had helped raise the yield level by 5-10% over the landraces, the gain through hybridization had been another 10-15%. Rice yields thus remained practically very low and stagnant until the launch of the Indica/Japonica Hybridization Programme by the FAO in 1952 aimed at recombining the fertilizer responsiveness of japonica rices and wide adaptability and preferred grain quality of indica rices. It was the earliest international effort to explore the possibilities of breaching the yield barrier in tropical rices.

A decade long ambitious Indica-Japonica project with CRRI at Cuttack (India) as the primary hybridization centre and major rice growing countries in the region for study of segregating populations of interest proved, however a disappointing experience. Persistent hybrid semisterility and skewed segregation towards parental types because of restricted recombination attributable to the failure, are now traceable to inappropriate choice of parents. Instead of temperate japonica, had breeders used sexually more compatible tropical japonica, the success level would have been closer to the targeted objective of yield enhancement. Mahsuri and Malinja selected and adopted in Malaysia and Adt 27 in India were the only products of value from this project. Mahsuri, the medium late semitall variety introduced later in India continues to be popular and ideally suited to long wet season and rainfed lowland ecologies. Its excellent grain quality being the preference of consumers, traders and millers alike, it is the choicest donor source of breeders all over for improvement of grain quality of varieties and hybrids. The high yielding varieties like Samba Mahsuri (GEB24/T(N)//Mahsuri) attracting premium price in the domestic market and occupying a very large area and ‘Swarna’ (Vasistha x Mahsuri), the widely popular in the irrigated long season and rainfed shallow lowland ecologies planted over 8 mill. ha in India and the adjoining countries like Bangladesh and fast spreading hybrids like DRRH 44, Sahyadri 4, etc are products of crosses involving Mahsuri as a parent. Adt 27, by virtue of its earliness and relatively higher response to high doses of fertilizer proved an ideal choice for the short ‘Kuruvai’ season in Tamil Nadu. Despite the disappointing outcome, the lesson learnt from the indica-japonica hybridization project that the key to raise the yield level of rice lies in making it fertilizer responsive and non-lodging, had in a way helped conceive and develop the semidwarf ideo type in the sixties.

 

13
Jul

Introduction

         Rice is the major staple food for 17 countries in Asia-Pacific, nine countries in North and South America and eight in Africa. Supplying 20 percent of the world’s dietary energy need, it constitutes 40-80 percent of the calories in the average daily intake of food of people in humid and sub-humid Asia (FAO, 2004; Hossain, 1999). More than 90 percent of rice is produced and consumed in Asia. Ironically, it was this tropical rice continent that remained chronically food deficit for long. Interestingly, it was the first to witness and adopt two landmark achievements in the history of rice breeding - the semidwarf plant type varieties that breached the centuries long yield barrier in the sixties and the hybrid technology that raised further the ceiling to genetic yield in the late seventies. Successively and together the two high yield technologies increased the global rice production by about one a half times (from 264 in 1965-67 to 642 million tonnes of unmilled rice in 2005-07) and productivity by two times (from 2.10 to 4.12 t/ha) during the last 40 years. The spectacular advance enabled many major rice growing countries including China and India attain and sustain self-sufficiency in rice and food since early eighties. Nearly four-fifths of the production advance has been due to vertical growth made possible through gradual replacement of traditional low yielding varieties by modern varieties of progressively higher and stable yields tailored for and extensively adopted in irrigated and mainly irrigated production environments (David and Otsuka, 1994; Pingali et al., 1997). They may be broadly grouped into first, second and third generation modern varieties evolved in keeping with the changing needs and priorities. The breeding priority of the 60s and 70s had been largely to evolve high yielding varieties of Taichung (Native)1 and IR8 plant type but of varied growth duration suiting different seasons/cropping systems and grain quality suiting diverse consumer preferences. Vulnerability to new pathogens and insect pests that appeared in increasingly devastative forms and caused recurrent and heavy yield losses necessitated change in breeding emphasis for insulating varieties with desired level of resistance to them resulting in the second generation modern varieties. Simultaneously, varietal improvement for relatively favourable rainfed ecologies and problem soils was initiated in countries, where they account for very large area. Sadly, the ongoing effort is yet to provide appropriate varietal solution to such handicapped ecologies. The third phase of rice breeding had been for breaching the potential yield of the semidwarf varieties through exploitation of hybrid vigour. Unlike in China, where hybrid rice technology was conceived and made a commercial reality since late 70s, outside China, the potential of the technology was not realized until mid 90s, when interest on heterosis breeding was revived in a few countries including India, Vietnam, Indonesia, The Philippines, Bangladesh, the USA and Egypt.

In the process of progressive varietal improvement, International Rice Research Institute (IRRI) since its establishment in 1960, the Food and Agriculture Organization (FAO) and the International Rice Commission under it since early fifties, the UNDP, the USDA, the Ford Foundation and the Rockefeller Foundation have played a seminal role. The outcome enabled many countries in the region and elsewhere to produce enough and meet their growing rice needs till recently. Since mid 80s the production-productivity growth however, started slowing down and by the current decade it declined to levels far less than that of population widening thereby the demand-supply gap in many countries in Asia. Achievement of the actual demand of 550 million tonnes of milled rice by 2025 would not be possible at the current level of production growth. To realize such a high target, the regionwise growth rate has to be 1.46, 1.29 and 0.58% respectively in South Asia, Southeast Asia and East Asia (Hossain 1998). The task is going to be quite challenging for countries like The Philippines, Bangladesh, India, Vietnam, Myanmar and Indonesia, which have to grow between 40 and 65 percent by 2025. Keeping the not so encouraging current demand-supply scenario and the fact that high and stable production growth of this ‘strategic commodity’ on a sustainable basis is vital for Asia to remain food secure (Hossain and Fischer, 1995) an attempt has been made in the present exercise, to review what has been achieved of the breeding research during the last four decades and discuss critically the socio-economic impact of it, the challenges ahead, research and development opportunities and strategies to meet them and remain self-sufficient and food secure.

 

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