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ID : 85296Ajouté le : 2005-07-21 10:12Mis à jour le : 2005-07-21 10:13Refreshed: 2012-02-11 23:32 
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Document(s) 29 de 38
Abstract: The Central Soils Salinity Research Institute (CSSRI) is a nodal institute in India with a national mandate for enhancing genetic resources and breeding crop varieties for salt-affected soils. During 25 years of research, it has had significant achievements. Indigenous and exotic germplasm resources involving traditional landraces and other adapted cultivars (along with their wild relatives) in rice, wheat, Indian mustard, barley and many other crops have been explored, collected, evaluated, utilized and conserved, saving them from rapid disappearance and genetic erosion. Some coastal landraces from highly specific habitats were not accepted by farmers of other states but they proved to be good donors. Experience has also revealed that the introduction of high yielding varieties for non-stress soils to problem soils, with the aim of increasing production, has not only resulted in yield failure but has also contributed to the genetic erosion of traditional landraces. Soon after this realization, systematic breeding was initiated for problem soils. There have been excellent results in the Rice Breeding Program, where a highly salt-tolerant dwarf, early maturing rice variety, CSR10, has been bred and released which combines salt-tolerance (from landraces) with high yields. It proved to be very effective on alkali soils when farmers were directly involved in adaptive research and demonstration. Continuous growing of this variety without any soil/chemical amendments reclaims alkali soils in three years to the extent that other crops like wheat, barley and mustard can also be grown. It has now become very popular among resource poor farmers. More than two and half dozen rice varieties have been bred for various types of salt tolerance. Studies revealed that there was no correlation between vegetative stage salinity tolerance and reproductive stage tolerance; and grain yield too. Reproductive stage salinity score is more reliable for grain productivity. K+ content exhibited a strong positive correlation with grain yield while Na+ content showed a poor negative correlation. Both additive and non-additive types of gene action, with a preponderance of additive types, was observed. The involvement of one group of genes having dominance for salinity tolerance and Na+/K+ ratio; and two groups of genes for K+ was observed. Isozyme studies demonstrated the presence of Est.21 in tolerant and Est. 22 in susceptible genotypes. The Indian Council of Agricultural Research- International Rice Research Institute (ICAR-IRRI) Collaborative Program for the Improvement of rice germplasm for saline soils, involving many countries in Asia and an Indian network consisting of target centers (hotspots) in eight states, has led to the development of more than 20 promising lines involving recombinants, anther culture derivatives, and somaclonal variants which are superior to many traditional local cultivars and landraces. Thus shuttle breeding has proved to be a model approach for developing salt-tolerant rice for sustainable productivity in fragile ecosystems. An Indo-U.K. (CSSRI-Sussex) Project on Soil salinity and breeding for salt-resistant crops has further strengthened our research program by inducing, through pyramiding, the desirable physiological and bio-chemical parameters related to salt-tolerance. CSSRI-UPLDC Adaptive Research has enhanced our activities by involving farmers as our partners in the evaluation and development of salt-tolerant crop varieties. This has now provided a practical and more reliable approach for germplasm collection and improvement at target sites. Farmers' participatory variety selection has been found to be more effective, especially for identifying abiotic stresses, as the varieties are exposed in the hot spots at target sites owned by farmers. No doubt, scientists' guidance will remain a pre-requisite since breeding for salt tolerance is highly complex involving multiple tolerances and because careful monitoring of stress is the basis for right selection and generation advancement. Farmers participation in later generation selection seems to be the ideal. No doubt, on-farm conservation of genes (in situ) by farmers will save the traditional landraces for problem soils, will maintain the evolutionary processes which shape new germplasm, and will guarantee the continual supply of germplasm to ex situ collections. IntroductionMeeting the increasing demands for food, forage, fibre and fuel will be a pressing challenge for the world community during the years ahead. This will require a larger production of biomass over a shrinking land area. Breeding crop varieties for increased salt tolerance is now considered as a more promising, energy-efficient and economical approach than major engineering processes and soil amelioration techniques which have gone beyond the limits of marginal farmers. Stresses under adverse soil conditions are highly complex and often compounded with climatic hazards. The stress varies from location to location and even from season to season. Soil stresses are often associated with nutritional imbalance (deficiency/toxicity). The interaction between soil stresses and other environmental factors influence the plant's response to that stress. Such complexities are responsible for the slow adaptability of high yielding crop varieties in adverse edaphic environments. It is, therefore, necessary that crop genotypes must be screened at target sites having adequate stresses in order to identify dependable sources of varietal tolerance. The on-going research at the Institute, including collaborative national and international research projects, has given CSSRI access to different target sites (hot spots) of the country and to various kinds of agroedaphic stresses. The Institute also benefits from a huge collection of donors/germplasm materials for salt tolerance in important crops; such genepools are necessary to provide the variability needed for successful breeding programs. Genetic diversity provides parental material from well-adapted landraces to enhance local adaptation. It helps to overcome susceptibilities to problem soil and also provides the foundation for breeding for novel requirements. Breeding now takes place from a much broader genetic base (greater number of varieties) in many crops. Genetic improvements can be easily adopted by resource-poor farmers for such problem soil environments where there are low-input conditions.Crop tolerance to sodicity/salinityLimit of crop toleranceThe tolerance limits for salinity and sodicity stresses differ in crops, halophytes and glycophytes. Such limits have been studied in the field and in artificially-controlled environments in pots and microplots. The extent of variability within the crop has also been observed. The limits of salt tolerance, with less than 50% reduction in productivity, are given in Table 1 and shown in Figure 1 for a range of crops.
Figure 1: Limit of salt tolerance in crops (based on 50% reduction in yield) Intra-crop variabilityIntra-crop variability reflects the future success of any breeding program in stress environments. Based on our work in sodicity and salinity stress over the years, the range of intra-crop variability is given in Table 2. Rice is found to have the maximum range of genetic variability for sodicity tolerance while barley has the maximum for salinity tolerance. The ranges of variability within some important crops are shown in Fig. 2.Varietal evaluation and improvementAll domesticated species have been derived from wild species and many progenitors of important species were those which pre-agricultural man gathered for food. In general, the wild relatives of crop plants have been used for breeding for resistance to diseases and pests but there are other significant prospects for utilizing these genepools. To date, these have been largely untapped by breeders and most existing collections are seriously deficient in such materials. The Institute has improved the scope of its varietal collections and also developed new varieties adapted to varying levels of salinity and sodicity stresses.
Figure 2: Range of intra-crop variability for alkalinity and salinity tolerance in selected crops Selection criteriaThe in situ performance of a variety and its reduction in grain yield at defined stress levels was followed in screening and evaluating our rice breeding materials and varieties. A high percentage of spikelet sterility relates to a low level of salt tolerance and was used in rice evaluation. Low Na+/K+ ratio of ion uptake is positively correlated with a high level of salt tolerance and was taken into consideration as a desired characteristic while screening the lines.The genotypes with high means (µ), regression values near to unity (bi) and the lowest deviations from regression (Sdi²) under multiple stress environments are selected as the most suitable, stable and adaptable genotypes for sustainable productivity in problem soils. Association studies reveal that the number of ear-bearing tillers, grains per panicle and panicle length, etc., are positively correlated with grain yield in rice. Screening techniquesScreening is an essential part of the commencement of a breeding program. The complexity of salt tolerance, heterogeneity in soils and significant interacting, environmental factors restrict a simple and reliable technique, i.e. that gives dependable results. Different methods which are followed for screening important crops and their varieties at this Institute are:a. Field evaluation: Screening work originally started at the Institute's naturally occurring, barren fields, which had been uncultivated for an unknown period. It was immediately realized that there was great variability, restricting the data processing and conclusions which could be drawn on the tolerant limits of the crops and their varieties. The gradient of soil sodicity was determined by soil tests at shortly-spaced intervals and a long strip running across the entire sodicity gradient has been allotted to each genotype. The plots generally consist of 2 to 3 rows for each variety, with each row 20 to 30 meters long. This allows comparable exposure of all genotypes to varying soil sodicity conditions. The layout for such a test generally consists of an incomplete block design, although a set of check varieties is replicated many times. The procedure increases the potential number of test varieties, allowing the simultaneous screening of a large number of genotypes. It is further possible to cut across the long plots in several parts to obtain varietal performance at varying levels of soil sodicity. There has thus been an overall increase in screening efficiency. This screening method is being used in rice, wheat, barley, pearl millet, oilseed and pulse crops. When the number of advanced materials is greatly narrowed, varieties are evaluated in a randomized block design with a maximum number of replications and with national and local checks to allow for initial yield evaluation. These further screened varieties are tested together with our developed varieties to determine yield ability; all are grown in bigger plot sizes to select for maximum productivity. The involvement of a greater number of checks has been shown more effective for data processing and for finalizing the tolerant lines. b. Microplots: The soil great heterogeneity and spatial variability restricts the reliable interpretation of the responses of genotypes. This problem spurred the construction and maintenance of mini-field environments having varying levels of salinity and sodicity. The device developed at the Institute consists of a series of dug-out cavity structures made of brick-mortar-concrete materials, measuring 2m x 2m, and 6m x 3m with a depth of about 0.8m and 1m respectively. They are filled with artificially prepared soil, so that the soil is uniform all through the profile. It is possible to create and maintain desired levels of sodicity and salinity in these microplots in a manner very much comparable to field conditions--but minus the soil heterogeneity. c. Pots: The edaphic environment of the pots is more or less uniform throughout the growth period of the plant in respect to the degree of stress. Sand culture and soil culture both are used in the pots for controlled studies in different crops. Studies of the genetics of salt tolerance and physiological experiments are carried out in these controlled and artificially-created varying stress environments. d. Others: Wooden trays are used for the studies on germination of different crop varieties. e. parmers' Participation Farmers are now involved through the CSSRI-UPLDC Adaptive research. Promising lines are evaluated at farmers' fields under the guidance of the Institute plant breeders. This has proven effective for evaluating the varietal adaptation and performance. Breeding methodsConventionalEvaluation and plant breeding work started with the collection, evaluation and systematic cataloguing of available Indian and exotic germplasm of rice, wheat, barley, pearl millet, oilseed, sugar, pulses etc. We followed a sequence of: introduction, different methods of selection, hybridization, mutation and shuttle breeding. The salt-tolerant varieties Damodar (CSR1) and Dasal (CSR2), and Getu (CSR3) are pure line selections of local traditional cultivars found in the Sunderban areas of West Bengal. These salt-tolerant varieties were later identified as possessing the genes for sodicity tolerance too. Hence CSR1 became one of the donors for salt tolerance in our hybridization program. A large number of segregants were advanced following the pedigree and modified bulk pedigree method. The varieties CSR10, CSR11, CSR12, CSR13, CSR18, CSR19, and CSR20 have been developed following the pedigree method. The advancement of generations was made following pedigree selection simultaneously in moderate stress and high stress sodicity and salinity environments, a method we call the `Parallel Pedigree Method' for the development of salt-tolerant varieties in problem soils. Backcross breeding has been used to induce salt tolerance in the prevailing genotypes. Similarly the wheat variety KRL 1-4 has been developed following the pedigree method. Mutation breeding has been used in rice, wheat and barley. Recurrent selection has been used in the case of bajra [pearl millet]. The pedigree and bulk methods have been used in barley. Shuttle breeding is being adopted in the development of salt-tolerant rices under the ICAR-IRRI Collaborative Project. More than two dozen varieties are being developed and tested in the national network program.Non-conventionalPromising salt-tolerant F1 anther culture derivatives: IR51500-AC-17, AC6534-1 and AC6534-4 are promising anther culture lines developed by the CSSRI-IRRI Collaborative Project.Biochemical markers for salt tolerance: Enzymes of basic metabolic pathways are often good indicators of response to biotic and abiotic stresses. One such enzyme is esterase which plays a role in lipid metabolism. The rice esterase 2 (Est2) locus is involved in the metabolism of cell membrane lipids. As salinity stress is also associated with the response of the cell membrane, it is expected that Est-2 locus would also influence the response of the carrier genotype to salinity stress. Preliminary studies with varieties involved in a diallel showed very encouraging results. Salt-tolerant donors Nona Bokra, Pokkali, CSR10, and CSR13 were having the isozyme pattern of Est 2¹, sensitive types IR28, MI-48, and Basmati 370 showed Est 2², while a tolerant cultivation CSR1 showed Est 2°. When they were grown in varying levels of salinity stress, the patterns were the same except in CSR1 with Est 2¹. CropsRiceRice is recommended as the first crop in a reclamation strategy for alkali soils. It can also being grown on inland saline soils when sufficient water is available. It is monocropped in coastal saline areas. The Institute first started its screening of traditional landraces in the early seventies in gypsum-treated sodic soil. The high yielding variety Jaya was used a check. Experimentation over the years has indicated that, under reclaimed conditions, the high yielding varieties perform better than traditional landraces. Further, the traditional landraces are tall and have poor agronomic characteristics. They have also proved to be adapted to specific sites and can not outperform in the sodic soils of the Indo-gangetic plains. After few years, it was realized that screening should take place in the actual stress environments and so we conducted pot culture experiments using varying levels of salinity and sodicity. The traditional salt-tolerant variety CSR1 (Damodar) was identified as a donor based on its less than 50% reduction in grain yield at soil ESP 73 (pH 10.1) and ESP 85 pH 10.3). Based on such results, the pot culture experiment was transferred to Gudha Farm where the variety CSR1 yielded 3 t/ha grain yield in the first year without any soil amendment. The other varieties Jaya, IR8, Pusa 2-21, and Basmati 370 failed because of high sterility. The continuous cultivation of CSR3 improved the soil and brought its ESP and pH to a level where other crops can now be grown. The variety CSR1 was very tall, late-maturing and unacceptable to farmers in this area and so it was used intensively in our hybridization and mutation breeding program for the development of dwarf, early and high yielding salt-tolerant rice varieties. High yielding rice varieties on normal soil, although available, fail to perform in salt affected soils. Therefore, a vast spectrum of genetic variability was screened for salinity/sodicity tolerance and many untapped and uneven unexplored genes were identified. A systematic breeding program at this Institute, following intensive hybridization and mutation breeding, has led to the development of many salt-tolerant rices adapted to varying levels of salinity and sodicity stress (Table 3).
Our first high yielding salt-tolerant early maturing rice variety, CSR 10, was released in 1989 for the sodic and inland saline soils of various zones across the country. This is the first dwarf, high yielding, salt-tolerant variety released by CVRC which can withstand the highly deteriorated alkaline (pH 9.8 - 10.2) and inland saline soil (ECe 6-11 dSm-1) conditions found in the transplanted irrigated management systems. CSR 10 (M 40-431-24-114/Jaya) is 80-85 cm tall, with a strong culm which prevents the lodging of plants. It matures in 120 days. The grain is short and bold with white rice and high amylose content. The yield potential of the variety is 5-6 t/ha under normal soil conditions while, under highly deteriorated salt-affected soils, grain yield ranges from 3.0 to 5 t/ha. In moderate stress, it yields from 5.0 to 5.5 t/ha. At breeding stations in multilocational AICRIP trials under salt stress, its yield was much higher than the salt-tolerant varieties Pokkali, Vikas and other high yielding varieties like Jaya. Under adaptive and minikit trials on farmers' fields, it yielded up to 4.9 t/ha in comparison to the local check varieties Saket 4 (1.5 - 2.4 t/ha), Sarju 52 (1.3 - 2.6 t/ha) and Jaya (2.2 - 3.0 t/ha). Marginal and poor farmers, who do not have enough resources to purchase chemical amendments to reclaim their fields, can use this variety as a biological amendment. The cultivation of this variety for three continuous seasons improves the soil sufficiently to enable most of the other crops to grow. Minikit and adaptive trials in Uttar Pradesh (U.P.) have confirmed the outstanding performance of this variety compared to the local varieties. This variety is presently the best salt-tolerant cultivar in the country which can be grown as biological amendment in highly deteriorated sodic soils having stress up to pH 10.2 (without any soil amendment). No other rice variety grows economically at this high stress level of sodicity. This variety has also excelled others in many countries and was rated as a very high salt-tolerant rice variety by IRRI in a global testing network. Sixteen demonstration trials were conducted by CSSRI at Mandanpur, Aligarh, (U.P.) with resource-poor marginal farmers. The trial included salt-tolerant the high yielding dwarf rice variety CSR 10 along with the local variety, in gypsum-treated and without gypsum-treated plots. The variety CSR 10 yielded more than 3.6 t/ha in salt-affected soils while the local variety miserably failed. This variety also performed best in many other parts of U.P. State. It has given more than 5 t/ha in the saline soils of Goa. The variety has also performed excellently in Gujarat, Maharashtra and Rajasthan. All-India evaluation of other salt-tolerant rice varieties in the national evaluation network demonstrated the excellent performance of some of our promising lines, including: CSR 11, CSR 12, CSR 13, CSR 18, CSR 19, CSR 20 and CSR 21. Other promising rice varieties include: CSR 12, CSR 13, CSR 18, CSR 19, CSR 20 CSR 21, CSR 22, CSR 23, CSR 24, CSR 25, CSR 26 and CSR 27. Most of them are recommended for sodic and saline soils of U.P., Haryana, Gujarat, Maharashtra, Andra Pradesh and Karnataka. Biological management of salt-affected soils: The biological management of salt-affected soils by growing the salt-tolerant rice variety CSR 10 has become successful without any chemical amendment. The variety yields 3.5 to 4.5 t/ha in the first year. It brings down the original soil pH from 10.2 to 9.9 after the crop harvest. In the second year, the yield goes beyond 4.5 t/ha and the pH level comes down to 9.7 and, in the third year, the pH remains around 9.5. Similarly the ESP comes down to 40, from 85. The soil physical characteristics are also improved. By the third year, the field becomes ideal for growing wheat or Indian mustard (raya) in the winter season. The variety has become very popular and is being grown in salt-affected soils in many states. Recommendations:
WheatVariability for salt tolerance has been observed in wheat varieties. Most of high yielding varieties can be grown in sodic soils only up to pH 9.1. Beyond this pH, only salt-tolerant varieties have the ability to survive and produce some economic yield. For saline stress, wheat varieties can be grown up to ECe 5-6 mmhos/cm. The KRL 1-4 wheat variety developed by this Institute was released in 1990. This variety is dwarf (85cm) with 145 days for maturity. The grain texture is hard, its color is amber with medium bold grain size. It yields 3.2 - 4.8 t/ha under non-stress and 3.4 t/ha under sodic stress up to pH 9.3. It also tolerates salinity stress up to ECe 7.The other promising lines developed by this Institute are KRL9, KRL10, KRL11, KRL12 and KRL13. The varieties PBW65, WH157, LOK1 and KRL4, KRL2-2-2 can tolerate up to pH 9.3, while Sonalika, HD22O4, HD2236, HD2177, RAJ 1972, HD1982 and IWP72 up to pH 9.1. The varieties HD2009, HD2329, WL711, C306 are medium-sensitive and HD4502, HD4530, Raj911, LSW34, N18622, N18622, Malwaraj, Jairaj and Moti are sensitive types which fail badly beyond the pH 8.8. Oilseed CropsIndian mustard (raya) has been recommended as best among the oilseed crops for both saline and sodic soils. It has relatively less irrigation and other inputs than wheat. Its salt tolerance limit is nearly same. Therefore, work has been intensified towards the development of salt-tolerant raya varieties. CS52, CS416, CSTR 330-1, CSTR 600-B-10, CSTR 610-10-1-1 and CS12 are the promising Institute breeding lines. The varieties Kranti, Varuna and Pusa bold have been identified as better tolerant cultivars. Among the other suitable oilseed crops, Brassica campestris var. toria has been observed as the second oilseed crop but its tolerance limit is less (up to pH 9.0) than that of Brassica juncea (up to pH 9.2). Taramira (Eruce sativa), a preferable crop of the dryland areas, has shown its limit of tolerance up to pH8.9. The other oilseed crops like safflower (Carthamus tinctorius) and sunflower (Halianthus annus) have miserably failed in sodic soils having pH 9.1. However, they seem to be promising in saline soils. Work for salinity stress is in progress. Linseed (Linum usitatissimum) has been observed to grow in sodic soil up to (pH 8.9) and in saline soil up to ECe 6. Soybean has also been observed as a promising crop for saline soils up to ECe 6 dSm-1.Pulses Pulses are found to be sensitive for salt-affected hazards. Work conducted at this Institute has already demonstrated that pulses, although sensitive, also have a good range of viability i.e. between and within the species. Among pulses, studies so far conducted at this Institute have revealed that cowpea (Vigna unguiculata) is moderately suitable up to pH 8.8, followed by Green gram (Vigna radiata). Pigeonpea (Cajanus cajan) has shown more susceptibility to sodic stress. Broad bean (Vicia faba), locally known as bakla, is showing relatively better tolerance to salinity up to ECe 7. Recent work has revealed that pea is better adapted to moderate sodicity (pH 8.9) followed by gram (pH 8.8). Millets Pearl millet is an important crop for saline soils of semi-arid areas. Pearl millet has been found to have proper growth and maturity up to ECe 10.0 dSm-1. However, the crop yields well to ECe 8 dSm-1. As the crop is sensitive to waterlogging, it is not suitable for sodic soils, where physical properties of such soils render low infiltration of water. The germination and flowering stages have been found to be relatively more sensitive stages in its plant growth. The bristled hybrid/populations have been observed to perform better than nonbristled ones in saline soils. In a nutshell, to have better growth of pearl millet in saline soils, the bold-seeded bristled varieties, preferably hybrids, should be sown after one or two rains so that excess salts are leached down before the sowing. The population/hybrids viz. GH3100 (Gujarat), ICH451 (ICRISAT), MBH10 (Mahyco), MBH137 (Mahyco), MBHV-82 (Hissar), ICMS8010 (ICRISAT) have been found promising in saline soils. BarleyAmong the winter crops, barley has been observed as one of the best for saline areas and it can be cultivated successfully up to ECe 10-12 dSm-1. It grows well in sodic soil up to pH 9.3 and the salt-resistant varieties can tolerate up to pH 9.4. The promising salt-tolerant varieties developed by this Institute are CSB1, CSB2, CSB3, CS-54 and CS 80-2. Among the other varieties DL200, Ratna, BH97, DL348, BL88, P469, DL352 are some promising cultivars for salinity and sodic stresses. Experiments under controlled stress environments of salinity and sodicity and field trials under saline and sodic soils exhibited very clearly that hulled barley varieties are more tolerant than hull-less varieties. Hull-less varieties were observed highly sensitive to saline and sodic soils. Barley varieties are better suited to saline soils than sodic soils.Sugar cropsAmong the sugar crops, sugarbeet is very tolerant to both salinity and sodicity stresses. The varieties Ramonskaya-06, Polyrava-E and Tribal can be successfully cultivated in highly sodic soil (pH 10.0) while for partially reclaimed sodic soil (pH 9.3), the variety Maribo Resistapoly is suitable. Under the saline soils (ECe 10 dSm-1), the variety Tribal has recorded the yield of 71.0 t/ha. Sugarcane varieties can be grown only up to pH 9.1 and the promising varieties are CO453, CO1341, CO6801, CO62329 and CO1111.ConclusionsBreeding rice varieties depends upon access to genetic resources including traditional landraces and wild relatives which are more adapted and have performed at a sustainable level in poor stress environments. Introduction of high yielding rices of irrigated ecosystems into fragile environments has not been productive and has resulted in the loss of local cultivars through the destruction of their habitats. Further, as the concept of ex situ conservation has gained currency in recent years, the notion of in situ or preserving biodiversity in its natural habitats has been diminished. Our explorations and collections of these landraces have revealed that a system of in situ or on-farm conservation has to be developed immediately, otherwise we will lose a wealth of biodiversity in fragile ecosystems. On-farm conservation keeps alive the evolutionary processes which lead to the generation of new genepools, and also maintains a continual supply of germplasm for ex situ needs. Our experience advocates that farmers' participation in varietal selection and their involvement in the final cycle of selecting breeding populations for stress environments in poor fragile ecosystems will be an ideal approach.Footnotes:1 R.K. Singh is a Rice Breeder at CSSRI-Karnal and D.Senadhira is a Plant Breeder and International Rice Research Institute Coordinator, Department of Plant Breeding, Genetic and Bio-Chemistry, IRRI. (See 'participant list' for address of first author.) (BACK)
Document(s) 29 de 38
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