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1.
Summary Improvement of durum wheat at the International Maize and Wheat Improvement Center (CIMMYT) was achieved by exploiting the variability of the tetraploid species in large numbers of combinations, and multi-location testing of germplasm on a world wide base. High yielding, widely adapted durums with short straw, good fertility, and adequate earliness were selected for distribution to major durum growing countries. Present attempts to improve durum wheat are directed at adjusting agronomic traits such as leaf angle and straw strength, and increasing spike fertility and spike size, thereby reaching higher grain numbers per unit area and higher yield potential. Diversification of the developmental pattern and incorporation of drought tolerance aim at further widening adaptation.  相似文献   

2.
CIMMYT's approach to breed for drought tolerance   总被引：4，自引：0，他引：4  
Summary About 32% of the 99 million ha wheat grown in developing countries experiences varying levels of drought stress. Three major drought types have been identified: Late drought (LD) is common in the Mediterranean region, early drought (ED) is found in Latin America and wheat is produced on residual soil moisture (RM) in the Indian subcontinent and part of Australia. Until 1983, CIMMYT selected all germplasm under near optimum conditions for its yield potential and tested only advanced lines under drought. In spite of many critics, this approach proved to be successful, since in the mid 80's CIMMYT germplasm was grown on 45% of the wheat area in LC with annual rainfall from 300–500 mm and on 21% in areas with less than 300 mm. Since 1983, CIMMYT's drought breeding methodology is to alternate segregating populations between drought stressed and fully irrigated conditions (FI) and to test advanced lines under a line source irrigation system. To compare the efficiency of these approach, yield of four, mostly leading varieties, from each of the regions with LD, ED, RM, and FI and twelve recent CIMMYT cultivars selected for high yield under FI and RM conditions (ALT) were compared under four different moisture regimes (FI, LD, ED, and RM) in 89–90 and 90–91 in Yaqui Valley, Mexico. Genotypic correlation between yield and days to flowering, days to maturity, height, grains m-2, TKW, test weight and grain fill period were calculated.Mean grain yield of the four best lines in the ALT group was highest under all moisture stress regimes, followed by the FI-group. However, the highest yielding cultivar within each moisture regime was from the FI-group under FI, from the LD-group under LD, and from the ALT-group under ED and RM conditions. Estimates for genetic advance suggest that FI is the best environment for increasing grain yield even in all three drought environments. This indicates that yield potential per se is beneficial also in drought environments. The highest yield in drought environments was realized by the CIM cultivars selected under FI and RM. Simultaneous evaluation of the germplasm under near optimum conditions, to utilize high heritabilities and identify lines with high yield potential, and under stress conditions to preserve alleles for drought tolerance seem at present the best strategy.  相似文献   

3.
Summary The International Spring Wheat Yield Nursery (ISWYN) has been distributed annually since 1964 and the results provide a base for investigating relationships among locations. Ordination and clustering of locations was conducted using 26 years of grain yield data. Ordination and clusters based on the discrimination of germplasm were compared with mega-environments, which are groupings of locations defined by CIMMYT on the basis of climatic factors and perceptions of major biotic and abiotic stresses. Discrepancies among mega-environmental groupings, clusters and ordinations may identify locations for which major stresses affecting wheat yield are yet unidentified.Major environmental discriminators were latitude and the presence or absence of stress, although there was little association of locations due to limited moisture availability. We identified two major spring wheat environments, typified as Asian and European, and suggest the mega-environmental classification does not explain all significant associations among locations. Location groupings based on discrimination of germplasm should be considered in parallel to mega-environments on a regular basis and we propose breeding for a base of broadly adapted germplasm to which specific stress tolerances are incorporated.Abbreviations CIMMYT International Maize & Wheat Improvement Centre - ISWYN International Spring Wheat Yield Nursery - WANA West Asia and North Africa  相似文献   

4.
Wheat is the second major staple crop, after rice, in India and Pakistan and is also gaining similar importance in Nepal and Bangladesh. Wheat production in South Asia has increased from 15 mt in 1960s to 95.5 mt during 2004–2005. It still needs to grow at the rate of 2–2.5% annually until the middle of 21st century. However, for India, recent estimations have shown a growth requirement of about 1.1%. Although the wheat improvement programs in these countries, with the active collaboration of national agricultural research centers (NARS) and CIMMYT, has made a significant progress, it is a matter of significant concern that wheat production has stagnated for last few years. Since there is little scope for increasing land area under wheat, the major challenge will be to break the yield barrier by pragmatic genetic and developmental approaches. The most serious constraints to wheat production in this region are a host of biotic and abiotic stresses. Although India has not faced any rust epidemic in the last decade, rusts continue to occupy the place of most dangerous pathogen for the region. Among the abiotic stresses, unusual warming trends during grain filling period are causing yield declines, especially in eastern and central India. There are other challenges that are specific to the highly productive rice–wheat cropping system predominant in the Indo-Gangetic plains. The total factor productivity of this system is declining due to depletion of soil organic carbon. Addition of organic matter to soil through green manuring and crop residue recycling, balanced fertilization, integrated nutrient management, diversification of rice-wheat system are some of the possible remedial measures to improve total factor productivity. The international linkages with CIMMYT needs to be strengthened more closely for developing more productive wheat genotypes and thus, achieving wheat targets in the South Asian region.  相似文献   

5.
Summary The dangers of a narrow genetic base of the world's major domesticated food crops have become a great global concern in recent decades. The efforts of the International Maize and Wheat Improvement Center (CIMMYT) to breed common wheat cultivars for resource poor farmers in the developing world (known as the Green Revolution wheats) has met with notable success in terms of improved yield, yield stability, increased disease resistance and utilization efficiency of agricultural inputs. However, much of the success was bought at the cost of an overall reduction in genetic diversity in the species; average Modified Roger's distances (MRD) within groups of germplasm fell from 0.64 in the landraces to a low of 0.58 in the improved lines in the 1980s. Recent efforts by CIMMYT breeders to expand the genetic base of common wheat has included the use of landraces, materials from other breeding programs, and synthetic wheats derived from wild species in the pedigrees of new advanced materials. The result, measured using SSR molecular markers, is a highly significant increase in the latent genetic diversity of recently developed CIMMYT breeding lines and cultivars compared to the original Green Revolution wheats (average MRD of the latest materials (0.63) is not significantly different from that of the landraces, as tested using confidence intervals). At the same time, yield and resistance to biotic and abiotic stresses, and end-use quality continue to increase, indicating that the Green Revolution continues to this day.  相似文献   

6.
Fusarium head blight (FHB) poses a challenge for wheat breeders worldwide; there are limited sources of resistance and the genetic basis for resistance is not well understood. In the mid-1980s, a shuttle breeding and germplasm exchange program launched between CIMMYT-Mexico and China, enabled the incorporation of FHB resistance from Chinese bread wheat germplasm into CIMMYT wheat. Most of the Chinese wheat materials conserved in the CIMMYT germplasm bank had not been fully characterized for FHB reaction under Mexican environments, until 2009, when 491 Chinese bread wheat lines were evaluated in a FHB screening nursery in Mexico, and 304 (61.9 %) showed FHB indices below 10 %. Subsequent testing occurred in 2010 for plant height (PH), days to heading (DH), and leaf rust response. In 2012, 140 elite lines with good agronomic types were further evaluated for field FHB reaction and deoxynivalenol (DON) accumulation. Most of the tested lines showed good resistance: 116 (82.9 %) entries displayed FHB indices lower than 10 %, while 89 (63.6 %) had DON contents lower than 1.0 ppm. Significant negative correlations were observed between FHB traits (FHB index, DON content, and Fusarium damaged kernels) and PH, DH, and anther extrusion. A subset of 102 elite entries was selected for haplotyping using markers linked to 10 well known FHB quantitative trait loci (QTL). 57 % of the lines possessed the same 2DL QTL marker alleles as Wuhan 1 or CJ 9306, and 26.5 % had the same 3BS QTL allele as Sumai 3. The remaining known QTL were of low frequency. These materials, especially those with none of the above tested resistance QTL (26.5 %), could be used in breeding programs as new resistance sources possessing novel genes for FHB resistance and DON tolerance.  相似文献   

7.
In order to update the available information on the main current and future constraints on wheat production and human capacity development, a survey covering nineteen developing countries, including major wheat producers, was conducted prior to the 2006 International Symposium on Increasing Wheat Yield Potential in Ciudad Obregon, Mexico. The results emphasize the substantial yield losses associated with a number of critical abiotic, biotic and socioeconomic constraints, and indicate their global prevalence. The most important constraints on wheat production are heat (affecting up to 57% of the entire wheat area in surveyed countries), competition with weeds, and diseases (both affecting up to 55% of wheat area). Of the socioeconomic constraints listed and evaluated by respondents, access to mechanization and availability of credit were the most often highlighted. The most-reported infrastructural constraints were insufficient resources for field station operations. When evaluating the importance of research partnerships to achieve national wheat program goals, respondents from all 19 countries assigned the highest importance to partnerships with international agricultural research centers. The most desired outputs from these include development and exchange of germplasm and assistance in capacity building and knowledge sharing. These findings confirm the anticipated constraints and needs over the next 10–20 years and affirm the importance of international agricultural research centers in providing support to address them.  相似文献   

8.
The main elements of the international wheat improvement program of the Centro Internacional de Mejoramiento de Maíz y Trigo (CIMMYT), also known as the International Maize and Wheat Improvement Center, have been shuttle breeding at two contrasting locations in Mexico, wide adaptation, durable rust and Septoria resistances, international multisite testing, and the appropriate use of genetic variation to enhance yield gains of subsequently produced lines. Such an approach yielded successes known collectively as the Green Revolution. However, at the beginning of the 21st century, this “cultivar assembly line” approach needs fine tuning to address crop needs under increasingly adopted resource conserving practices, as well as those related to nutritional requirements of the end-users. International wheat improvement will therefore focus on the targeting of traits in respective mega-environments, and the use of participatory methods, especially in marginal environments. The main features of this wheat improvement strategy include the introduction of new and novel sources of genetic variation through wild species, landraces, and, potentially, the use of transgenes for intractable traits. This variation will be combined using international shuttle breeding, and increased breeding efficiency will be achieved through marker-aided methods, more targeted use of crop physiology, plant genetics, biostatistics, and bioinformatics. Likewise, CIMMYT will increase its focus on the needs of end-users by emphasizing regional efforts in participatory research and client-oriented plant breeding.  相似文献   

9.
India is the second largest producer of wheat in the world, with production hovering around 68–75 million tons for past few years. The latest estimated demand for wheat production for the year 2020 is approximately 87.5 million tons, or about 13 million tons more than the record production of 75 million tons harvested in crop season 1999–2000. Since 2000, India has struggled to match that record production figure and thus faces a critical challenge in maintaining food security in the face of its growing population. The current major challenges facing future wheat production in India are increasing heat stress; dwindling water supplies for irrigation; a growing threat of new virulence of diseases such as wheat rusts (yellow, brown, and black) and leaf blight; continuous adoption of rice-wheat systems on around 11 million hectares; changes in urbanization patterns, and demand for better quality wheat. In addition, the threat posed by the new stem rust race Ug99 can not be underestimated. The wide gap (around 2.5 t/ha) between the potential and harvested yield in the eastern Gangetic Plains also cries out for solutions. Addressing issues related to different stresses will require harnessing genes discovered in landraces and wild relatives following conventional as well as non-conventional approaches. For effective technology delivery in areas that suffer from poor linkages with farmers, participatory research needs to be strengthened. The future germplasm requirements from a dependable collaborator such as CIMMYT are largely being dictated by the above factors.  相似文献   

10.
本文采用田间人工接种方法研究了部分含CIMMYT玉米种质的半外来群体选系对丝黑穗病的抗性。结果表明在用CIMMYT种质Pob45和Pob46与黑龙江省部分自交系杂交构建的半外来群体的选系中,对丝黑穗病中抗及其以上的选系占一半以上,其中高抗占35.9%。CIMMYT种质的引进总体上有利于提高黑龙江省种质资源对丝黑穗病的抗性。  相似文献   

11.
Moisture stress greatly limits the productivity of wheat in many wheat-growing regions of the world. Knowledge of the degree of genetic diversity among parental materials for key selection traits will facilitate the development of high yielding, stress tolerant wheat cultivars. The objectives of this study were to: (i) use amplified fragment length polymorphisms (AFLPs) to assess genetic diversity among bread wheat lines and cultivars with different responses to drought stress in two distinct environments and, (ii) compare genetic diversity estimated by AFLPs with diversity evaluated on agronomic performance under drought stress. Twenty-eight genotypes, 14 from Iran and 14 developed or obtained by CIMMYT, were evaluated in the study. Phenotypic data on the 14 Iranian lines were obtained in Iran, and data on the 14 CIMMYT lines were collected in Mexico. Ten AFLP primer pairs detected 335 polymorphic bands among the 28 cultivars. At the 5th fusion level of the resulting dendrogram, 6 genotype clusters were identified. Thirteen of the 14 CIMMYT genotypes grouped into one cluster while 4 of the remaining groups were comprised only of Iranian genotypes. When the agronomic performance of the Iranian materials was compared with the AFLP diversity analysis, 5 of the 6 drought susceptible genotypes clustered together in the agronomic dendrogram, and were located in the same cluster in the AFLP dendrogram. However, the drought tolerant Iranian materials did not show the same degree of relationship. The CIMMYT materials did not demonstrate a significant association between agronomic performance and genetic diversity determined using AFLPs. Clearly these data show that there are genotypes with similar agronomic performance and different genetic constitutions in this study that can be combined in a breeding program to potentially improve tolerance to drought stress.  相似文献   

12.
Understanding the relationships among testing environments is essential for better targeting cultivars to production environments. To identify patterns of cultivar, environment, cultivar-by-environment interactions, and opportunities for indirect selection for grain yield, a set of 25 spring wheat cultivars from China and the International Maize and Wheat Improvement Center (CIMMYT) was evaluated in nine environments in China and four management environments at CIMMYT in Cd. Obregon, Mexico, during two wheat seasons. Genetic background and original environment were the main factors influencing grain yield performance of the cultivars. Baviacora M 92, Xinchun 2 and Xinchun 6 showed relatively more stable and higher grain yields, whereas highly photoperiod sensitive cultivars Xinkehan 9, Kefeng 6 and Longmai 19 proved consistently inferior across environments, except in Harbin and Keshan, the two high latitude environments. Longmai 26, also from high latitude environments in the north-eastern Heilongjiang province, was however probably not as photoperiodicly sensitive as other cultivars from that region, and produced much higher grain yield and expressed a broader adaptation. None of the environments reported major diseases. Pattern analyses revealed that photoperiod response and planting option on beds were the two main factors underlying the observed interactions for grain yield. The production environment of planting on the flat in Mexico grouped together with Huhhot and Urumqi in both wheat seasons, indicating an indirect response to selection for grain yield in this CIMMYT managed environment could benefit the two Chinese environments. Both the environment of planting on the flat with Chinese Hejin and Yongning, and the three CIMMYT environments planting on raised beds with Chinese Yongning grouped together only in one season, showing that repeatability may not be stable in this case.  相似文献   

13.
Plant breeders are always interested in new genetic resources. In thepast, the sources have been limited to existing germplasm. Geneticengineering now provides the opportunity for almost unlimited strategies tocreate novel resources. As a first stage, the Applied Biotechnology Center(ABC) at CIMMYT developed a method for the mass production of fertiletransgenic wheat (Triticum aestivum L.) that yields plants ready fortransfer to soil in 13–14 weeks after the initiation of cultures, and, over thecourse of a year, an average production of 5–6 transgenic plants per day.CIMMYT elite cultivars are co-bombarded with marker gene and a gene ofinterest with co-transformation efficiencies around 25–30%. The reliabilityof this method opens the possibility for the routine introduction of novelgenes that may induce resistance to diseases and abiotic stresses, allow themodification of dough quality, and increase the levels of micronutrientssuch as iron, zinc, and vitamins. The first group of genes being evaluatedby the ABC are the pathogenesis related (PR) proteins, such as thethaumatin-like protein (TLP) from barley, chitinase, and 1–3-glucanase. Stable integration of the genes in the genome andinheritance in the progeny were determined by phenotypical analyses thatchallenged the plants against a wide range of pathogens. Using these genes,we have recovered more than 1200 independent events (confirmed byPCR and Southern blot analyses) that show responses to the pathogens thatrange from tolerance to hypersensitive reactions. The quantity andanti-fungal activity of the endogenous thaumatin-like proteins were analyzedin T1 and T2 progeny plants. Western blot analyses showeddifferent protein patterns of the wheat endogenous TLPs. Preliminary resultsindicated that some patterns increased the resistance of transgenic wheatplants to Alternaria triticina. This relationship is being furtherinvestigated.  相似文献   

14.
回交导入后代水稻种质有利基因的鉴定与筛选研究   总被引：18，自引：0，他引：18  
种质资源蕴藏着品种遗传改良的各种有利基因,高效发掘种质资源的有利基因是实现育种突破的前提。本研究选择IR64、特青和新株型（NPT）为轮回亲本与13个供体的不同回交世代（BC2F2-BC4F2）群体为材料,进行耐盐、耐淹和褐稻虱抗性鉴定与筛选。结果表明,尽管多数亲本本身对这些逆境不具备很好抗性或耐性,但在绝大多数回交后代中均出现耐盐、耐淹和抗褐稻虱的超亲分离,表明这些供体均带有对这些性状的有利基因。这种潜在“隐蔽”有利基因的表达受遗传背景影响较大。从总体上看,3个性状的选择效率以IR64背景最高,特青背景高于NPT背景。BC2对耐盐性的选择效率明显高于BC3和BC4代,BC3和BC4的选择效率因不同组合而异。研究表明通过大规模回交导入和回交后代性状的严格鉴定是发掘种质资源有利基因的有效途径。  相似文献   

15.
Bread wheats (Triticum aestivum L.) were evaluated for plant characteristics contributing to grain yield and plant adaptation under various drought patterns. The usefulness of these traits as explicit selection criteria in developing drought tolerant wheat varieties was investigated in three experiments. Cultivars from four germplasm groups, representing the four relevant major and distinct global wheat growing environments, were grown under the respective simulated early, late, continuous and no drought conditions by manipulating irrigation in north western Mexico. Additionally, 560 advanced lines from the CIMMYT breeding program were grown under late drought conditions, and 16 randomly selected advanced genotypes were studied in more detail under late and no drought conditions. In these three studies, the association between yield in drought-stressed environments and yield in non drought-stressed environments was interpreted to reflect genotypic high yield potential, mainly by way of high biomass development. However, yield potential only partly explained the superior performance under drought. For each pattern of drought stress, particular and often different plant traits were identified that further contributed specific adaptation to the distinct drought stress conditions. Knowledge of these traits will be useful for developing CIMMYT germplasm for specific drought-stressed areas. Ultimately, these studies demonstrate that both yield potential and specific adaptation traits are useful criteria in breeding for drought environments, and should be combined to achieve optimum performance and adaptation to drought stress. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

16.
The past few decades have witnessed hundreds of family-based linkage studies mapping for numerous traits but only a limited number of QTLs were actually cloned, tagged, or used for marker-assisted selection. Although providing valuable information, this conventional approach cannot be scaled up to underpin the incredible amount of phenotypic variation in the form of 266, 589 hexaploid wheat accessions maintained in public germplasm collections. Association mapping has recently emerged as an alternative and more powerful mapping approach where a natural population is surveyed to determine marker-trait associations using linkage disequilibrium (LD). After its first application for milling quality in 2006, association mapping studies in hexaploid wheat are being extended to tag yield traits, protein quality, and tolerance to biotic and abiotic stresses. Advances in genotyping technology and statistical approaches greatly accelerated the shift from conventional linkage-based mapping to LD-based association mapping. Association mapping stands out because of simultaneous utilization of a large number of ex situ-conserved natural variation due to historical recombination events accumulated over centuries.  相似文献   

17.
A.J. Worland  E.J. Sayers  V. Korzun 《Euphytica》2001,119(1-2):157-161
A microsatellite marker WMS261 developed at I.P.K., Gatersleben,Germany, co-segregates with the semi-dwarfing gene Rht8. Screens ofover 800 wheat varieties from 20 countries show 90% carry WMS-261alleles with 165, 174 or 192 base pairs (bp). The 192bp allele diagnosticof Rht8 occurs in most screened Southern European varieties. Anallele with 165 bp occurs in the majority of CIMMYT Mexican varieties andin most varieties bred in countries that utilize CIMMYT germplasm.Agronomic studies of single chromosome recombinant line mappingpopulations segregating for WMS 261 alleles with 165, 174 or 192 bp,show compared to the 174bp allele the 192bp allele reduces height byaround 8 cm and the 165 bp allele increases height by around 3cm. Theresults indicate the importance and widespread utilization of Rht8 asa dwarfing gene in southern Europe and suggest an adaptative significanceto the height promoting 165 bp allele in CIMMYT material.  相似文献   

18.
Global wheat (Triticum aestivum L.) production must increase 2% annually until 2020 to meet future demands. Breeding wheat cultivars with increased grain yield potential, enhanced water-use efficiency, heat tolerance, end-use quality, and durable resistance to important diseases and pests can contribute to meet at least half of the desired production increases. The remaining half must come through better agronomic and soil management practices and incentive policies. Analyses of the recent International Yield Trials indicate that grain yields of the best new entries were usually 10% higher than the local checks globally, as well as within a country across sites. Variation in yield across sites within a country/region underline the role of genotype × environment (GE) interaction and provides opportunities to select for stable genotypes, which is not often done. The lack of proper analysis undermines proper utilization of germplasm with high yield potential and stability in the national wheat breeding programs. Some of the best performers in irrigated areas were amongst the best in semiarid environments, reinforcing the fact that high yield potential and drought tolerance can be improved simultaneously. The best performing lines often had genotypic base of widely adapted genotypes Kauz, Attila, Baviacora, and Pastor, with genetic contributions from other parents including synthetic wheat. We recommend within country multilocation analysis of trial performance for a crop season to identify lines suiting particular or different locations within a country. The immediate feedback on GE interaction will also help in breeding lines for countries having substantial variation across locations and years.  相似文献   

19.
大白菜(Brassica rapa ssp.pekinensis)是中国种植面积较大的蔬菜作物之一,其不仅可以为人体补充维生素C和维生素E,对预防心血管疾病也有很大的帮助。大白菜在生长发育过程中受许多不利环境的影响,包括盐碱胁迫、水涝胁迫、重金属胁迫、温度胁迫等非生物胁迫,以及病虫害等生物胁迫。这些胁迫会引起大白菜发生一系列的变化,不仅会影响大白菜体内相关基因的表达,还会影响细胞的代谢和生长发育等过程。在这些胁迫下,大白菜自身能产生一定的抗逆性,但随着胁迫的增加,其自身产生的抗逆性不足以抵抗环境中较严重的非生物胁迫和生物胁迫,胁迫的影响使得大白菜不能正常生长甚至死亡,从而导致大白菜减产,造成市场供应不足的现象发生。本综述总结了近年来非生物胁迫和生物胁迫对大白菜生长的影响,并对大白菜应对胁迫而产生的抗逆性进行了概括,以期为后续的大白菜抗逆性研究提供参考。  相似文献   

20.
Rice, with its wide geographic distribution extending from 50°N to 35°S, is expected to be the most vulnerable cultivated crop to future changing climates. Among the different abiotic stresses, extreme temperatures coinciding with critical developmental stages, increasingly frequent floods and drought spells, and worsening sea water inundation are some of the major threats to sustainable rice productivity. Following the successful implementation of molecular marker‐assisted backcrossing to introgress large‐effect QTL for submergence tolerance in rice mega varieties, rice breeding for drought, salinity and, recently, heat tolerance is employing the same approach. Although tolerance for combined submergence and salinity has been achieved, developing rice varieties with multiple tolerance for other abiotic and biotic stresses and finding the appropriate agronomic package to exploit their performance remain a challenge. The major bottleneck is the lack of unidentified large‐effect QTL for other abiotic stresses that are strongly influenced by genotype × environment (G × E) interaction. Rapid advances in the use of molecular tools, including a plethora of SNP markers, are expected to facilitate the development of major abiotic stress‐tolerant rice. In response to the actual farmer field situation, progress achieved in understanding and developing independent abiotic stress tolerance is being exploited to combine tolerances (for example, heat and drought; salinity and submergence) to address emerging environmental problems across a wide range of rice ecosystems.  相似文献   

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