Showing papers on "Plant breeding published in 2007"

Molecular Markers in a Commercial Breeding Program

Abstract: In the 1980s, DNA-based molecular markers were identified as having the potential to enhance corn (Zea mays L.) breeding. Research has demonstrated the advantage of using molecular markers for selection of simply inherited traits, however only a few studies have evaluated the potential to enhance genetic gain for quantitative traits. In the late 1990s, Monsanto decided to implement marker assisted selection for quantitative traits in our global plant breeding programs. We built genotyping systems and information tools and developed marker assisted methodologies that increased the mean performance in elite breeding populations.

Quantitative trait loci for phytate in rice grain and their relationship with grain micronutrient content

Abstract: Phytate (inositol-hexa-phosphate) has an important role in plants but it also may have anti-nutritional properties in animals and humans. While there is debate within the plant breeding and nutrition communities regarding an optimum level in grain, there appears to be little information at the molecular level for the genetics of this trait, and its association with important trace elements, in particular, Fe and Zn. In this preliminary study, quantitative trait loci (QTL) for grain phytates, Zn and Fe in glasshouse-grown rice lines from an IR64 x Azucena doubled haploid population were identified. Correlations between phytate and essential nutrients were also studied. Transgressive segregation was found for most traits. Phytate and total P concentrations had one QTL in common located on chromosome five with the (high concentration) allele contributed from Azucena. There were significant positive correlations between phytate and inorganic phosphorus (P), total P, Fe, Zn, Cu and Mn concentrations for both grain concentration and content. However, the QTLs of phytate were not located on the same chromosomal regions as those found for Fe, Zn and Mn, suggesting that they were genetically different and thus using molecular markers in breeding and selection would modify the phytate level without affecting grain micronutrient density.

Breeding triple rust resistant wheat cultivars for Australia using conventional and marker-assisted selection technologies

Abstract: Stem rust susceptibility of European wheats under Australian conditions posed a significant threat to wheat production for the early British settlers in Australia. The famous Australian wheat breeder, William Farrer, tackled the problem of stem rust susceptibility through breeding fast-maturing wheat cultivars. South-eastern Australia suffered a severe stem rust epidemic in 1973, which gave rise to a national approach to breeding for rust resistance. The National Wheat Rust Control Program was set up in 1975, modelled on the University of Sydney’s own rust resistance breeding program, at the University of Sydney Plant Breeding Institute, Castle Hill (now Cobbitty). Back-crossing of a range of sources of resistance provided genetically diverse germplasm for evaluation in various breeding programs. Current efforts are directed to building gene combinations through marker-assisted selection. Major genes for resistance to stem rust and leaf rust are being used in the back-crossing program of the ACRCP to create genetic diversity among Australian germplasm. Stripe rust and to a lesser extent leaf rust resistance in the Australian germplasm is largely based on combinations of adult plant resistance genes and our knowledge of their genomic locations has increased. Additional genes, other than Yr18/Lr34 and Yr29/Lr46, appeared to control adult plant resistance to both leaf rust and stripe rust. Two adult-plant stem rust resistance genes have also been identified. The development of selection technologies to achieve genotype-based selection of resistance gene combinations in the absence of bioassays has evolved in the last 5 years. Robust molecular markers are now available for several commercially important rust resistance genes. Marker-assisted selection for rust resistance is performed routinely in many wheat-breeding programs. Modified pedigree and limited back-cross methods have been used for breeding rust-resistant wheat cultivars in the University of Sydney wheat-breeding program. The single back-cross methodology has proved more successful in producing cultivars with combinations of adult plant resistance genes.

Scale and Complexity in Plant Systems Research : Gene-Plant-Crop Relations

Abstract: Preface: Genetics of plant performance: from molecular analysis to modeling: 1. Genetic and molecular analysis of growth responses to environmental factors using Arabidopsis thaliana natural Variation M. Reymond et al.- 2. From QTLs to genes controlling root traits in maize R. Tuberosa and S. Salvi.- 3. Multi-trait multi-environment QTL modelling for drought stress adaptation in maize M. Malosetti et al .- 4. Accounting for variability in the detection and use of markers for simple and complex traits S.C. Chapman et al.- 5. An integrated systems approach to crop improvement G.L. Hammer and D.R. Jordan.- 6. Crop systems biology: an approach to connect functional genomics with crop modeling X. Yin and P.C. Struik.- Modelling genotype x environment interactions: 7. A modelling approach to genotype x environment interaction:genetic analysis of the response of maize growth to environmental conditions W. Sadok et al.- 8. Modelling genotype x environment x management interactions to improve yield, water use efficiency and grain protein in wheat S. Asseng and N.C. Turner.- 9. Physiological processes to understand genotype x environment interactions in maize silking dynamics L. Borras, M.E. Westgate and J.P. Astini.- 10. Modelling the genetic basis of response curves underlying genotype x environment interaction F.A. van Eeuwijk, M. Malosetti and M.P. Boer.- Physiology and genetics of crop adaptation: 11. Physiological interventions in breeding for adaptation to abiotic stress M.P. Reynolds and R.M. Trethowan.- 12. Physiological traits for improving wheat yield under a wide range of conditions G.A. Slafer and J.L. Araus.- 13. Is plant growth driven by sink regulation? Implications for crop models, phenotyping approaches and ideotypes M. Dingkuhn et al.- 14. Yield improvement associated with Lr19 translocation in wheat: which plant attributes are modified? D.J. Miralles, E. Resnicoff and R. Carretero.- Physiology and modelling of crop adaptation: 15.Simulation analysis of physiological traits to improve yield, nitrogen use efficiency and grain protein concentration in wheat P. Martre et al.- 16. An architectural approach to investigate maize response to low temperature K. Chenu et al.- 17. Tillering in spring wheat: a 3D virtual plant-modelling study J.B. Evers and J. Vos.- 18. Use of crop growth models to evaluate physiological traits in genotypes of horticultural crops E. Heuvelink et al.- Diversity, resource use and crop performance: 19. Role of root clusters in phosphorus acquisition and increasing biological diversity in agriculture H. Lambers and M.W. Shane.- 20. Prospects for genetic improvement to increase lowland rice yields with less water and nitrogen S. Peng and B.A.M. Bouman.- 21. Exploiting diversity to manage weeds in agro-ecosystems L. Bastiaans et al.- Outlook and dialogue: 22. When can intelligent design of crops by humans outperform natural selection? R.F. Denison.- 23. Integrated assessment of agricultural systems at multiple scales M.K. van Ittersum and J. Wery.- 24. A dialogue on interdisciplinary collaboration to bridge the gap between plant genomics and crop sciences P.C. Struik et al.- List of reviewers

The successful application of a marker-assisted wheat breeding strategy

Abstract: A number of useful marker-trait associations have been reported for wheat. However the number of publications detailing the integrated and pragmatic use of molecular markers in wheat breeding is limited. A previous report by some of these authors showed how marker-assisted selection could increase the genetic gain and economic efficiency of a specific breeding strategy. Here, we present a practical validation of that study. The target of this breeding strategy was to produce wheat lines derived from an elite Australian cultivar ‘Stylet’, with superior dough properties and durable rust resistance donated from ‘Annuello’. Molecular markers were used to screen a BC1F1 population produced from a cross between the recurrent parent ‘Stylet’ and the donor parent ‘Annuello’ for the presence of rust resistance genes Lr34/Yr18 and Lr46/Yr29. Following this, marker-assisted selection was applied to haploid plants, prior to chromosome doubling with cochicine, for the rust resistance genes Lr24/Sr24, Lr34/Yr18, height reducing genes, and for the grain protein genes Glu-D1 and Glu-A3. In general, results from this study agreed with those of the simulation study. Genetic improvement for rust resistance was greatest when marker selection was applied on BC1F1 individuals. Introgression of both the Lr34/Yr18 and Lr46/Yr29 loci into the susceptible recurrent parent background resulted in substantial improvement in leaf rust and stripe rust resistance levels. Selection for favourable glutenin alleles significantly improved dough resistance and dough extensibility. Marker-assisted selection for improved grain yield, through the selection of recurrent parent genome using anonymous markers, only marginally improved grain yield at one of the five sites used for grain yield assessment. In summary, the integration of marker-assisted selection for specific target genes, particularly at the early stages of a breeding programme, is likely to substantially increase genetic improvement in wheat.

Genetic diversity of cowpea [Vigna unguiculata (L.) Walp.] in four West African and USA breeding programs as determined by AFLP analysis

Abstract: Cowpea is an important grain legume and hay crop of many tropical and subtropical regions, especially in the dry savanna region of West Africa. The cowpea gene pool may be narrow because of a genetic bottleneck during domestication. Genetic variation within specific breeding programs may be further restricted due to breeding methods, ‘founder effects’ and limited exchange of germplasm between breeding programs. Genetic relationships among 60 advanced breeding lines from six breeding programs in West Africa and USA, and 27 landrace accessions from Africa, Asia, and South America were examined using amplified fragment length polymorphism (AFLP) markers with six near infrared fluorescence labeled EcoRI + 3/1bases/MseI + 3/1bases primer sets. A total of 382 bands were scored among the accessions with 207 polymorphic bands (54.2%). Despite a diverse origin, the 87 cowpea accessions shared a minimum 86% genetic similarity. Principal coordinates analysis showed clustering of breeding lines by program origin, indicating lack of genetic diversity compared to potential diversity. Accessions from Asia and the Americas overlapped and were distinct from West African breeding lines, indicating that germplasm from Asia and the Americas have common origins outside West Africa. US and Asian breeding programs could increase genetic variability in their programs substantially by incorporating germplasm from West Africa, while national programs in West Africa should consider introgression of Asian germplasm and germplasm from other parts of Africa into their programs to ensure long-term gains from selection.

Did Modern Plant Breeding Lead to Genetic Erosion in European Winter Wheat Varieties

Abstract: The objective of this study was to assess whether modern plant breeding has led to any loss of genetic diversity in modern European winter wheat varieties (Triticum aestivum L.). For this purpose, a collection of 511 widely grown winter wheat varieties of Central and Northern Europe was genotyped with 42 microsatellite markers. In the varieties representing the National List of the UK during the 1980s and 1990s the allelic richness and gene diversity were lower than in the varieties of Recommended Lists covering the time period 1945– 2000. However, no apparent quantitative loss of genetic diversity was found by comparing the different decadal groups of varieties present in the Recommended Lists. Analysis of molecular variance (AMOVA) showed that the variance component among varieties within decadal groups accounted for 96.41% of the genetic variation, but among decadal groups only for 3.59%. The Fst values increased from the 1950s to the 1990s compared to the 1940s with a slight decrease in the 1970s. These results suggested that modern plant breeding has resulted in changes of alleles present in the germplasm; however, it appears that modern plant breeding has resulted in no apparent loss of allele numbers, or genetic diversity, in the investigated European wheat varieties over time.

Molecular markers and doubled haploids in European plant breeding programmes

Abstract: The breeding companies and laboratories involved in this article cover a wide range of crops grown in the temperate climate zone: small grain cereals, oilseed crops, forage crops, turf, vegetables and potato. Speed and efficiency are becoming increasingly important in variety breeding and doubled haploids (DH) and genetic markers are important biotechnological tools to accelerate materials to market. Collaborative research between universities, research institutions and breeding companies has resulted in the routine use of DH technology and molecular markers in practical breeding of barley, wheat and rapeseed. DH populations have been established not only for barley, wheat and rapeseed, but for rye, oat and triticale, where DH technology is less developed. A driver here is the value of the crop e.g. although wheat is less responsive to DH production the value of the end product makes the effort worthwhile. Simple and rapid DNA extraction methods used in high-throughput marker assisted selection (MAS) systems are essential for routine use of markers. MAS is used both to monitor the presence of genes of interest and also to monitor the genetic background. DH technology in forage, turf and vegetables is still in progress and the practical use of markers in all crops is limited by access to trait linked markers. Collaboration and technology transfer with universities, research institutions and breeding companies is essential for the improvement of both DH protocols in recalcitrant crops and marker technology in all crops.

History, Contribution, and Future of Quantitative Genetics in Plant Breeding: Lessons From Maize

Abstract: The time frame of the history of quantitative genetics is similar to Mendelian genetics. The rediscovery of Mendel's laws of inheritance in 1900 was the basis for determining the inheritance of quantitative traits and for developing plant breeding and selection methods. Because of the differences expressed by many of the leading geneticists relative to importance of continuous vs. discontinuous variation in evolution, the acceptance of the concepts for the study of quantitative genetics was delayed. R.A. Fisher, S. Wright, and J.B.S. Haldane were the primary early contributors for developing the theory and methods for studying the inheritance of quantitative traits. Greater interest in the inheritance of quantitative traits in plants occurred after 1946, primarily because of the heterosis expressed in maize (Zea mays L.) hybrids. During the past 50 yr, extensive research has been conducted to determine the relative importance of different genetic effects in the inheritance of quantitative traits for most cultivated plant species. Quantitative genetic research has contributed extensive information to assist plant breeders in developing breeding and selection strategies. Directly and/or indirectly, the principles for the inheritance of quantitative traits are pervasive in developing superior cultivars to meet the food, feed, fuel, and fiber needs the world demands. The principles of quantitative genetics will have continued importance in the future, but at different levels. Information from molecular genetics research will be integrated with our current knowledge at the phenotypic level to increase the effectiveness and efficiency of plant breeding.

Genetic diversity of canadian soybean cultivars and exotic germplasm revealed by simple sequence repeat markers

Abstract: Genetic diversity assessment of improved crop germplasm can facilitate the expansion of the genetic base in a plant breeding program, but little effort has been made to assess the Canadian soybean [Glycine max (L.) Merr.] gene pool established over the past century. Simple sequence repeat (SSR) markers were applied to assess the genetic diversity of 45 Canadian soybean cultivars released from 1934 to 2001 and 37 exotic germplasm accessions. Thirty-seven SSR primer pairs were applied and 234 polymorphic bands were scored for each accession. The frequencies of the scored bands ranged from 0.01 to 0.90 and averaged 0.17. The proportion of total SSR variation occurring between exotic and Canadian germplasm was 9%; among the Canadian cultivars of three breeding periods 10%; and between the cultivars of maturity groups 0 and 00 4%. More diversity was found for exotic germplasm than the Canadian. More diversity was observed in the cultivars of the recent breeding period than the early. The Canadian cultivars were clustered into seven major groups, partially congruent to the known pedigrees, and they were more related to germplasm from Russia, Sweden, and Ukraine and less to the Asian germplasm. The six genetically most distinct cultivars were PS86 RR, Gaillard, Manitoba Brown, Beechwood, Maple Isle, and 92B91. These findings are useful for the selection of genetically distinct or less related soybean materials to improve the genetic background of the soybean gene pool.

New oilseed rape (Brassica napus) hybrids with high levels of heterosis for seed yield under nutrient-poor conditions

Abstract: Winter oilseed rape (Brassica napus L.) is the most important oil crop in Europe. Due to a continually increasing demand for rapeseed oil for food and non-food uses, the production of hybrid cultivars with higher seed and oil yields has become increasingly important in recent years. However, the systematic use of heterosis for hybrid breeding in oilseed rape is limited by the relatively narrow genetic basis of adapted germplasm, which can impede the generation of distinct heterotic pools. In the present study experimental hybrids were developed from a population of 190 DH lines derived from a cross between an elite, double-low seed quality (zero erucic acid, low glucosinolate content) winter oilseed rape variety and a semi-synthetic line derived from a genetically diverse resynthesised rapeseed line with high erucic acid and glucosinolate contents. The DH lines were crossed with a male sterile tester and the resulting test hybrids were examined for yield performance at two locations in Hesse, Germany, that exhibit extreme differences in climatic conditions and soil characteristics. Mid-parent heterosis for seed yield was determined at both the agronomically optimal location Rauischholzhausen and the marginal site Niederhörlen. A value of up to 43% mid-parent heterosis for seed yield could be observed among selected test hybrids compared to that of their parental DH lines. The heterosis level for yield was particularly high at the nutrient-poor site, where the best test hybrids showed significantly higher yields than elite open-pollinating and hybrid varieties. This demonstrates the suitability and adaptability of highly heterotic rapeseed hybrids on marginal locations and suggests the existence of a strong heterotic effect on nutrient uptake efficiency.

Haploid and Doubled Haploid Technology

Abstract: The microspore culture technique has its wide applications in plant genetic research and breeding programmes in oilseed Brassicas due to its relative simplicity, efficiency in haploid and doubled haploid production, mutation and germplasm generation, and gene transformation. Various factors could influence microspore embryogenesis and haploid production including donor plant genotype, donor plant physiology, microspore developmental stage, culture conditions, culture environment and pretreatments. Stress is also an essential component during embryogenesis induction in microspore culture. Efficient plant regeneration from microspores mostly occurs through direct embryogenesis ensuring minimal occurrence of cytogenetic abnormalities. Appropriate stress conditions such as chilling, partial desiccation, cotyledon excision, and successive subculture of microspore-derived embryos could promote plant development in oilseed rape. Medium renovation, phytohormones and plant growth regulators, and chromosome doubling agents such as colchicine treatment also affect plant regeneration in Brassica species. Compared to colchicine treatments of microspore-derived embryos and plants, immediate colchicine treatment of isolated microspores results in high embryogenesis and diploidisation and low chimeric percentages. The ploidy level of microspore-derived plants of Brassica species could be estimated by different methods at various stages. Mutation breeding techniques are widely used in plant breeding for producing useful mutants and variants. Microspore culture also provides an ideal method for mutation because the mutated traits can be fixed in homozygous condition by chromosome doubling, which can enforce to obtain target mutation traits efficiently. Ultraviolet irradiation, mutagenic agents ethyl methane sulphonate and sodium azide could be applied to isolated microspores and the derived embryos of rapeseed. Utilization of microspore-derived embryos for production of desired traits such as the altered fatty acids, disease resistance and glucosinolate compositions through mutagenesis and selection is advancing and also discussed.

Fifty years of wheat breeding in Southern Brazil: yield improvement and associated changes

Abstract: The objective of this study was to assess the impact of genetic breeding on grain yield, and to identify the physiological traits associated to the increment in yield and their related growth processes, for wheat cultivars grown in Southern Brazil, in the past five decades. Seven wheat cultivars released between 1940 and 1992, were compared for physiological aspects associated with grain yield. Grain yield, biological yield, biomass partitioning, harvest index and grain yield components were also determined. The number of grains per square meter was more affected by plant breeding and was better correlated with grain yield (r = 0.94, p<0.01) than with grain weight (r = -0.39 ns ). The higher number of grains per square meter was better correlated with the number of grains per spike in the modern cultivars than in the older ones. The genetic gain in grain yield was 44.9 kg ha -1 per year, reflecting important efforts of the breeding programs carried out in Southern Brazil. Grain yield changes, during the period of study, were better associated with biomass production (r = 0.78, p<0.01) than with harvest index (r = 0.65, p<0.01).

Pulses, sugar and tuber crops.

Abstract: Common Bean.- Pea.- Cowpea.- Mungbean.- Lentil.- Chickpea.- Genome Mapping and Molecular Breeding in Lathyrus.- Pigeonpea.- Quinoa (Chenopodium quinoa).- Bambara Groundnut.- Sugarcane.- Potato.- Sweetpotato.- Cassava.- Yams.

Rice cv. Bahia mutagenized population: a new resource for rice breeding in the Mediterranean basin

Abstract: In the Mediterranean basin, the limited availability of rice genetic resources restricts the success of breeding programs. Although mutation induction is a powerful alternative to generate desired novel variations, current rice mutant resources have little relevance in the Mediterranean breeding programs that require well-adapted cultivars for maximum performance. In this work a genome-wide mutation induction has been used on rice cv Bahia, a japonica cultivar well adapted to the Mediterranean climate and cultural practices, to increase its genetic variability and to facilitate the generation and selection of interesting agronomical traits. Bahia mutant collections were generated by irradiating seed batches with either 30 Gy fast neutrons or 250 Gy gamma rays. After initial screening of M2 plants and followed by evaluation of M3 and M4 generations in open field, elite genotypes were selected. The selected lines carried morphological and physiological changes of agronomical interest such as earliness, culm height reduction, yield increase and spontaneous spots appearance in leaves. The mutants are useful as breeding materials for improving varieties in the Mediterranean.

Plant regeneration through callus initiation from mature embryo of Triticum

Abstract: The behaviour of diverse Triticum genotypes in the tissue culture response of mature embryo callus was compared, and factors affecting tissue culture response were studied in this paper. Significant differences were detected in callus induction, embryogenic callus differentiation, plantlet regeneration and culture efficiency when mature embryos of 31 plants of different Triticum species were compared. These were the main wheat cultivars of the Chinese northern winter-type wheat region and breeding lines (Triticum aestivum L.), durum wheat (Triticum durum Desf.), cultivable emmer wheat (Triticum dicoccum Schuble) and the common wheat progenitors Triticum dicoccoides and Triticum aegilopides. The genotype dependency was particularly high in tissue culture of mature embryos of these Triticum genotypes. The efficiency of induction, differentiation and regeneration of mature embryos callus was high in genotypes selected out. Mature embryo-derived callus of HB341, TS021, SN2618, T. dicoccum, HB188, and T9817 showed better tissue culture response than the other genotypes. Plantlets can be regenerated from mature embryo-derived callus of 31 genotypes, saving on growth facility resources and time required for the collection of other explants, and providing a solid basis for the genetic transformation and molecular plant breeding of Triticum plants.

Genetic Variability among Maize Cultivars Grown in Ekiti-State, Nigeria

Abstract: An appreciable level of variation within crop varieties is essential to initiate and sustain crop improvement using plant breeding methods. A field experiment was conducted with the aim of estimating variation among maize cultivars grown in Ekiti State. Twenty maize cultivars obtained from various locations within the state was evaluated between April to August 2005 at the Teaching and Research Farm, University of Ado-Ekiti. The twenty cultivars constituted the treatment, which was lied out in a Randomized Complete Block Design with three replicates. Result shows that there were significant (p<0.05) difference for in day to first silking and anthesis, days to 50% anthesis and silking, plant and ear heights, leaf blight and curvularia leaf spot and grain yield. Grain yield ranges from 3.02 t ha for Ijelu and 4.91 t ha for Ilupeju. Phenotypic and 11 genotypic variance was highest for plant and ear heights and least for the foliar disease rating and significant for all the traits except ear plant . Broad sense heritability estimates ranged from 0.16 for ear plant to 0.71 for 11 Curvularia leaf spot. Correlation coefficient was positive and significant between grain yield and both plant and ear heights, but negative with Curvularia leaf spot. These results are suggestive that the cultivars evaluated in this study are good candidates on which improvement activates can be initiated the incorporation of high grain yield traits would also have a long run advantage.

Induced Mutations For Enhancing Salinity Tolerance in Rice

Abstract: Salt accumulation in soil surfaces, known as soil salinity, could lead to the impairment of plant growth and development and is manifested mostly under irrigated and dryland agriculture. Excess salts in the soil affects plants through osmotic stress; accumulation to toxic levels within the cells; and through the interference with the uptake of mineral nutrients. Rice productivity in several parts of the world is therefore severely limited by salinity on account of the prevalence of irrigation in rice farming. Tolerance to salt toxicity in plants is a genetic and physiologically complex trait. Halophytes (salt tolerant plants) are different from the salt-sensitive glycophytes in terms of peculiarities in their anatomy, ability to sequester otherwise toxic ions, and other physiologic processes. It is logical therefore to infer complexity also at the genetic level on account of the several pathways involved in these mechanisms. These complexities have confounded genetic improvement strategies for salinity tolerance in plants resulting in a paucity of saline tolerant plants, with only about 30 officially released saline tolerant crop varieties world-wide. Only one saline tolerant rice variety, Bicol, has been officially released to farmers. We review strategies being currently employed in the development of saline tolerant rice varieties. These include conventional plant breeding which is hampered by the lack of suitable genetic variation for this trait; the modest progress made through doubled haploidy; and the reliance on somaclonal variation, an unsustainably unpredictable strategy. This review also posits that while genetic transformation has led to the modification of certain physiological indices implicated in salinity tolerance in rice, in isolation, these modifications have not been translated to improved yield under salt stress. A more recently adopted strategy, induced mutagenesis, has led to some promising results. We argue that the production of induced rice mutants holds the greatest promise of these strategies for mitigating the scourge of soil salinity considering the relative ease with which other traits in this crop have been modified using this methodology. The underlying principles of induced mutagenesis; the modes of action of different mutagenic agents; and procedures for the rapid production and detection of mutants are also summarised. In order to enhance efficiency in the production, detection and incorporation of induced mutants into crop improvement programmes, we suggest the coupling of in vitro (such as doubled haploidy and cell suspension cultures) and molecular genetic techniques to this methodology. It is posited also that the efficiency of this process can be greatly enhanced by marker-aided selection while high throughput reverse genetics strategies could lead to the rapid detection of mutation events in target genes. It is concluded that with the plethora of genomics resources available for rice, the use of induced mutations for improving salinity tolerance (and other traits) would rely significantly on the concerted application of efficiency enhancing in vitro techniques and functional genomics strategies (including reverse genetics)

Optimization of the Marker-Based Procedures for Pyramiding Genes from Multiple Donor Lines: II. Strategies for Selecting the Objective Homozygous Plant

Abstract: For extended application of marker-based plant breeding, strategies are discussed for selecting a high-degree gene-pyramided line from among progeny of a multiparentally produced heterozygous plant (root genotype). A strategy with combined use of haplo-diploidization and crossing between selected plants will be highly efficient; selection starts with haplo-diploidized plants raised from the root genotype, and in the absence of a plant with the objective marker genotype, two plants with the best complementary genotypes are crossed to produce a hybrid, which in turn is haplo-diploidized for the next round of selection. In this strategy, even a plant having as many as 20 target markers can be obtained at an almost perfect certainty in about three rounds of selection with a maximum of 200 tested plants per round. When haplo-diploidized plants are unavailable, a plant with the most promising marker genotype should be selected and self-fertilized in each generation, or in the absence of any promising plant, two plants with the best complementary genotypes are crossed for the next round of selection. In this strategy, the number of tested plants in the first two generations counts when the markers are codominant, whereas the rounds of selection counts when the markers are dominant. Of various supplementary measures for this strategy, backcrossing the root genotype with one of the donors could be useful when the donor has more than 70% of all targeted markers.

Genetic evidence for gametophytic selection of wilt resistant alleles in chickpea

Abstract: Gametophytic selection can drastically reduce the number of selection cycles during crop improvement programs. The objective of the present investigation was to test whether the nature of inheritance of two unlinked disease-resistant loci, h1 and h2, against Fusarium wilt in chickpea (Cicer arietinum L.) under gametophytic (pollen) selection was similar to that already observed at sporophytic level. A homozygous dominant (H1H1H2H2) susceptible genotype JG-62 was crossed to a recessive (h1h1h2h2) resistant genotype WR-315 to produce 20 F1 hybrid seeds. In the following generation, flower buds of 10 F1 hybrid plants were subjected to toxin stress before anthesis and the remaining ten control F1 plants’ flowers were sprayed with water. Thirty-four selected BC1 plants were generated by test crossing resistant WR-315 individuals with pollen from toxin-stressed F1 individuals. Both control and treated F1 plants were selfed to produce respective F2 generations. Two DNA markers, CS-27700bp and A07C430bp, linked to susceptible alleles H1 and H2, respectively, were used to study the inheritance patterns of h1 and h2 loci in the F2 and BC1 generations. One hundred and forty-four selected F2, 129 control F2, and 34 selected backcross individuals were tested for the presence or absence of DNA markers. Except for the control F2, observed ratios of selected F2 and BC1 populations exhibited significant chi-square deviations from expected monogenic and digenic ratios. Our results suggest that gametophytic selection is as effective as that realized at the sporophytic level, and that the gametophytic selection can be an effective breeding tool for plant breeding programs.

Leaf rust of spring wheat in Northern Kazakhstan and Siberia: incidence, virulence, and breeding for resistance

Abstract: Northern Kazakhstan and Western Siberia of Russia represent a relatively uniform continuous area of spring wheat cultivation of ~20 million ha. Despite the dry climate, cultivation of susceptible varieties resulted in epidemics of leaf rust on average in 1 year out of 4, affecting up to 5 million ha with yield losses of up to 25–30%. The leaf rust population showed absence of virulence for genes Lr9 and Lr24 and low frequency of isolates with virulence to Lr11, Lr16, Lr18, and Lr28. The field observations indicated that genes Lr28 and Lr36 provide resistance. All the wheat cultivars are susceptible to leaf rust and only recently have several resistant lines and new varieties have been tested in trials. The current resistance breeding efforts are based on incorporation of the resistance from local and foreign sources. The breeding strategy is not based on detailed knowledge of the leaf rust population and its interaction with the host because of limited pathology and genetics research capacity. However, practical breeding efforts in combining proven resistance with adaptation traits resulted in the development of new competitive resistant germplasm. Shuttle breeding between the region and CIMMYT-Mexico to enhance resistance contributes to regional efforts.

Exploitation of Natural Biodiversity Through Genomics

Abstract: The genetic improvement of crop plants is the most viable approach to meeting the increasing demand for agricultural output. This goal may be achieved by using the wealth of genetic variation provided by nature. Until now, scientists have been unable to exploit the genetic potential warehoused in plant germplasm repositories for quantitative traits associated with agricultural yield. Here we review the development and application of the advanced-backcross and introgression-line breeding populations for the identification of wild species derived chromosome segments that improve agricultural performance of elite germplasm. The results of studies in a wide range of crops indicate that, unlike their domestic relatives, which are often depleted in genetic variation, wild populations of plants carry a tremendous wealth of potentially valuable alleles, many of which would not have been predicted from the phenotype of the wild plants. The results from these studies may help open up new sources of genetic variation for plant breeding and biotechnology and shed light on the nature of quantitative trait variation.

Powdery mildew resistance in 155 Nordic bread wheat cultivars and landraces.

Abstract: The occurrence and distribution of seedling resistance genes and the presence of adult plant resistance to powdery mildew, was investigated in a collection of 155 Nordic bread wheat landraces and cultivars by inoculation with 11 powdery mildew isolates. Eighty-nine accessions were susceptible in the seedling stage, while 66 accessions showed some resistance. Comparisons of response patterns allowed postulation of combinations of genes Pm1a, Pm2, Pm4b, Pm5, Pm6, Pm8 and Pm9 in 21 lines. Seedling resistance was three times more frequent in spring wheat than in winter wheat. The most commonly postulated genes were Pm1a+Pm2+Pm9 in Sweden, Pm5 in Denmark and Norway, and Pm4b in Finland. Forty-five accessions were postulated to carry only unidentified genes or a combination of identified and unidentified genes that could not be resolved by the 11 isolates. Complete resistance to all 11 isolates was present in 18 cultivars. Adult plant resistance was assessed for 109 accessions after natural infection with a mixture of races. In all, 92% of the accessions developed less than 3-5% pathogen coverage while nine lines showed 10-15% infected leaf surface. The characterization of powdery mildew resistance in Nordic wheat germplasm could facilitate the combination of resistance genes in plant breeding programmes to promote durability of resistance and disease management.

Agronomic performance and the effect of self-fertilization on German winter faba beans.

Abstract: Faba bean is mostly grown as spring crop in Central Europe; additionally it is grown as winter crop in few mild areas of UK and France. A genetically divers winter bean population selected for high winter hardiness and very promising as winter crop in Germany was studied here. The population was assessed for its agronomic performance as well as for the effect of inbreeding depression due selfing using an open-pollinated generation and two inbred generations developed from it. The assessment was carried out at four environments in two successive seasons (2001 and 2002) at Goettingen, Central Germany. The open-pollinated population showed better performance in overwintering ability than the UK checks but equivalent performance in yield and other agronomic traits. Winter damage, plant height and yield suffered from inbreeding depression proving heterosis in the open-pollinated generation. Overwintering ability and yield were shown to exhibit a mid parent heterosis of about 32% and of about 75%, respectively. Application of the results in breeding of synthetic cultivars is discussed.

Compositions and methods of plant breeding using high density marker information

Abstract: The present invention relates to breeding methods to enhance the germplasm of a plant. The methods describe the identification and accumulation of preferred haplotype genomic regions in the germplasm of breeding populations of maize (Zea mays) and soybean (Glycine max). The invention also relates to maize and soybean plants comprising preferred haplotypes.