Showing papers on "Plant breeding published in 2010"

Prediction of genetic values of quantitative traits in plant breeding using pedigree and molecular markers.

Abstract: The availability of dense molecular markers has made possible the use of genomic selection (GS) for plant breeding. However, the evaluation of models for GS in real plant populations is very limited. This article evaluates the performance of parametric and semiparametric models for GS using wheat (Triticum aestivum L.) and maize (Zea mays) data in which different traits were measured in several environmental conditions. The findings, based on extensive cross-validations, indicate that models including marker information had higher predictive ability than pedigree-based models. In the wheat data set, and relative to a pedigree model, gains in predictive ability due to inclusion of markers ranged from 7.7 to 35.7%. Correlation between observed and predictive values in the maize data set achieved values up to 0.79. Estimates of marker effects were different across environmental conditions, indicating that genotype × environment interaction is an important component of genetic variability. These results indicate that GS in plant breeding can be an effective strategy for selecting among lines whose phenotypes have yet to be observed.

Plant Breeding for Water-Limited Environments

Abstract: Water scarcity or drought is one of the major constraints in agricultural productivity and food security regardless of the availability of rigorous management practices for healthier crop development. Crop losses under waterlimited conditions mainly depend on time, intensity, and duration of water stress. These losses can be reduced by changing the genetic architecture of the plants to improve performance. Plant Breeding for Water-Limited Environments is an excellent attempt to discuss a broad spectrum of knowledge and expertise regarding drought determinants at physiological, biochemical, and genetic levels, and the latest technologies to manipulate these determinants for better crop/plant performance. The book consists of seven chapters, each highlighting specifi c issues/challenges in water-limited environments. The introductory chapter, “The Moisture Environment,” provides a nice overview regarding various forms of drought, its classifi cation, and the major decision support systems/software/models available to plant breeders to integrate the knowledge of moisture environment to devise a successful breeding project. The next chapter, “Plant Water Relations, Plant Stress, and Plant Production,” focuses on the plant–water relationship under water defi cit conditions and the role of abscisic acid (ABA) and various plant organs (root, stem, leaf, stomata, cuticle, etc.) for plant adaptation to this stress and reduction in growth and development. The author describes the eff ect of drought stress on various growth stages of crops with ‘fl owering’ being the most crucial and sensitive growth stage. The most important coping mechanism to deal with the eff ects of drought, according to the author, is the introduction of genetic resistance in the crop cultivars that are discussed in Chapter 3, “Drought Resistance and its Improvement.” The author emphasizes that traditional plant breeding methods involving yield as a selection index and multi-environmental yield trials are slow and costly whereas the involvement of physiological selection in a breeding program for drought tolerance can off er a direct improvement in releasing resistant cultivars. The deployment of genomics, transgenic, and marker-assisted selection for drought resistance is considered a problematic approach unless it is well synchronized with traditional breeding methods. The components of drought, i.e., dehydration avoidance, dehydration tolerance, drought escape, and summer dormancy, along with water use effi ciency, are discussed. Chapter 4, “Phenotyping and Selection,” has been divided into two sections. In the fi rst section, the author elaborates on techniques to manage a uniform drought stress profi le for an entire experiment, both in the fi eld and the greenhouse, and concisely discusses: the concerns relating to the soils of experimental stations and comparing it to real dryland soils, coping with rainfall interference during experiments with manual and automated rainout shelters, and the procedure/method to attain a desirable drought stress at particular plant growth stage with the pros and cons of various irrigation systems. The second section illustrates the protocols to appropriately phenotype the plants exhibiting dehydration avoidance and dehydration tolerance. The author argues that the quality and quantity of phenotyping is really crucial to making progress in breeding for drought stress. The complexity of drought stress expression and its subsequent measurements are highlighted in three dimensions—plant growth stage, stress development rate, and peak level of water when

Molecular Plant Breeding

Abstract: 1. Introduction 2. Molecular Breeding Tools: Markers and Maps 3. Molecular Breeding Tools: Omics and Arrays 4. Populations in Genetics and Breeding 5. Plant Genetic Resources: Management, Evaluation and Enhancement 6. Molecular Dissection of Complex Traits: Theory 7. Molecular Dissection of Complex Traits: Practice 8. Marker-assisted Selection: Theory 9. Marker-assisted Selection: Practice 10. Genotype-by-environment Interaction 11. Isolation and Functional Analysis of Genes 12. Gene Transfer and Genetically Modified Plants 13. Intellectual Property Rights and Plant Variety Protection 14. Breeding Informatics 15. Decision Support Tools.

Managing Phenol Contents in Crop Plants by Phytochemical Farming and Breeding—Visions and Constraints

Abstract: Two main fields of interest form the background of actual demand for optimized levels of phenolic compounds in crop plants. These are human health and plant resistance to pathogens and to biotic and abiotic stress factors. A survey of agricultural technologies influencing the biosynthesis and accumulation of phenolic compounds in crop plants is presented, including observations on the effects of light, temperature, mineral nutrition, water management, grafting, elevated atmospheric CO2, growth and differentiation of the plant and application of elicitors, stimulating agents and plant activators. The underlying mechanisms are discussed with respect to carbohydrate availability, trade-offs to competing demands as well as to regulatory elements. Outlines are given for genetic engineering and plant breeding. Constraints and possible physiological feedbacks are considered for successful and sustainable application of agricultural techniques with respect to management of plant phenol profiles and concentrations.

Genetic diversity, inter-gene pool introgression and nutritional quality of common beans (Phaseolus vulgaris L.) from Central Africa.

Abstract: The Great Lakes region of Central Africa is a major producer of common beans in Africa. The region is known for high population density and small average farm size. The common bean represents the most important legume crop of the region, grown on over a third of the cultivated land area, and the per capita consumption is among the highest in the world for the food crop. The objective of this study was to evaluate the genetic diversity in a collection of 365 genotypes from the Great Lakes region of Central Africa, including a large group of landraces from Rwanda as well as varieties from primary centers of diversity and from neighboring countries of Central Africa, such as the Democratic Republic of Congo and Uganda, using 30 fluorescently labeled microsatellite markers and automated allele detection. In addition, the landraces were evaluated for their seed iron and zinc concentration to determine if genetic diversity influenced nutritional quality. Principal coordinate and neighbor-joining analyses allowed the separation of the landraces into 132 Andean and 195 Mesoamerican (or Middle American) genotypes with 32 landraces and 6 varieties intermediate between the gene pools and representing inter-gene pool introgression in terms of seed characteristics and alleles. Genetic diversity and the number of alleles were high for the collection, reflecting the preference for a wide range of seed types in the region and no strong commercial class preference, although red, red mottled and brown seeded beans were common. Observed heterozygosity was also high and may be explained by the common practice of maintaining seed and plant mixtures, a coping strategy practiced by Central African farmers to reduce the effects of abiotic and biotic stresses. Finally, nutritional quality differed between the gene pools with respect to seed iron and zinc concentration, while genotypes from the intermediate group were notably high in both minerals. In conclusion, this study has shown that Central African varieties of common bean are a source of wide genetic diversity with variable nutritional quality that can be used in crop improvement programs for the region.

Modeling and mapping QTL for senescence-related traits in winter wheat under high temperature

Abstract: Senescence is a genetically programmed and environmentally influenced process resulting in the destruction of chlorophyll and remobilization of nutrients to younger or reproductive parts of plants. Delayed senescence, or stay-green, contributes to a long grain-filling period and stable yield under stress. To model senescence and identify quantitative trait loci (QTL) for the trait, a population of recombinant inbred lines (RIL) from a cross between winter wheat cultivars, ‘Ventnor’ and ‘Karl 92’ was evaluated for heat tolerance under optimum temperature of 20/15°C (day/night) and continuous heat stress of 30/25°C from 10 days after anthesis (DAA) until maturity. Ventnor is a heat-tolerant cultivar and Karl 92 is a relatively heat-susceptible cultivar. Green leaf area was measured and used to model percent greenness retained over the reproductive period. Chlorophyll content and chlorophyll fluorescence were recorded on flag leaves. Senescence was converted to a quantitative trait using the model. Based on the modeled parameters, the RILs were categorized into three groups. When senescence-related traits were evaluated, nine QTL for heat tolerance were found on chromosome 2A, two each on chromosomes 6A and 6B and one each on chromosome 3A, 3B, and 7A. Both parents contributed favorable alleles for most of the senescence-related traits. Microsatellite markers Xgwm356 and Xgwm5 prominently linked to the senescence-related traits may be useful in marker-assisted breeding. These and the linked AFLP (amplified fragment length polymorphism) markers XCGT.TGCG-349, XCGT.GTG-343, and XCGT.CTCG-406, if converted to STS (sequence tagged sites), can be used for further molecular dissection of the QTL for post-anthesis heat tolerance.

Sodium exclusion QTL associated with improved seedling growth in bread wheat under salinity stress

Abstract: Worldwide, dryland salinity is a major limitation to crop production. Breeding for salinity tolerance could be an effective way of improving yield and yield stability on saline-sodic soils of dryland agriculture. However, this requires a good understanding of inheritance of this quantitative trait. In the present study, a doubled-haploid bread wheat population (Berkut/Krichauff) was grown in supported hydroponics to identify quantitative trait loci (QTL) associated with salinity tolerance traits commonly reported in the literature (leaf symptoms, tiller number, seedling biomass, chlorophyll content, and shoot Na+ and K+ concentrations), understand the relationships amongst these traits, and determine their genetic value for marker-assisted selection. There was considerable segregation within the population for all traits measured. With a genetic map of 527 SSR-, DArT- and gene-based markers, a total of 40 QTL were detected for all seven traits. For the first time in a cereal species, a QTL interval for Na+ exclusion (wPt-3114-wmc170) was associated with an increase (10%) in seedling biomass. Of the five QTL identified for Na+ exclusion, two were co-located with seedling biomass (2A and 6A). The 2A QTL appears to coincide with the previously reported Na+ exclusion locus in durum wheat that hosts one active HKT1;4 (Nax1) and one inactive HKT1;4 gene. Using these sequences as template for primer design enabled mapping of at least three HKT1;4 genes onto chromosome 2AL in bread wheat, suggesting that bread wheat carries more HKT1;4 gene family members than durum wheat. However, the combined effects of all Na+ exclusion loci only accounted for 18% of the variation in seedling biomass under salinity stress indicating that there were other mechanisms of salinity tolerance operative at the seedling stage in this population. Na+ and K+ accumulation appear under separate genetic control. The molecular markers wmc170 (2A) and cfd080 (6A) are expected to facilitate breeding for salinity tolerance in bread wheat, the latter being associated with seedling vigour.

Genetic mapping of QTLs for sugar-related traits in a RIL population of Sorghum bicolor L. Moench.

Abstract: The productivity of sorghum is mainly determined by quantitative traits such as grain yield and stem sugar-related characteristics. Substantial crop improvement has been achieved by breeding in the last decades. Today, genetic mapping and characterization of quantitative trait loci (QTLs) is considered a valuable tool for trait enhancement. We have investigated QTL associated with the sugar components (Brix, glucose, sucrose, and total sugar content) and sugar-related agronomic traits (flowering date, plant height, stem diameter, tiller number per plant, fresh panicle weight, and estimated juice weight) in four different environments (two locations) using a population of 188 recombinant inbred lines (RILs) from a cross between grain (M71) and sweet sorghum (SS79). A genetic map with 157 AFLP, SSR, and EST-SSR markers was constructed, and several QTLs were detected using composite interval mapping (CIM). Further, additive x additive interaction and QTL x environmental interaction were estimated. CIM identified more than five additive QTLs in most traits explaining a range of 6.0-26.1% of the phenotypic variation. A total of 24 digenic epistatic locus pairs were identified in seven traits, supporting the hypothesis that QTL analysis without considering epistasis can result in biased estimates. QTLs showing multiple effects were identified, where the major QTL on SBI-06 was significantly associated with most of the traits, i.e., flowering date, plant height, Brix, sucrose, and sugar content. Four out of ten traits studied showed a significant QTL x environmental interaction. Our results are an important step toward marker-assisted selection for sugar-related traits and biofuel yield in sorghum.

Development and application of gene-based markers for the major rice QTL Phosphorus uptake 1

Abstract: Marker-assisted breeding is a very useful tool for breeders but still lags behind its potential because information on the effect of quantitative trait loci (QTLs) in different genetic backgrounds and ideal molecular markers are unavailable. Here, we report on some first steps toward the validation and application of the major rice QTL Phosphate uptake 1 (Pup1) that confers tolerance of phosphorus (P) deficiency in rice (Oryza sativa L.). Based on the Pup1 genomic sequence of the tolerant donor variety Kasalath that recently became available, markers were designed that target (1) putative genes that are partially conserved in the Nipponbare reference genome and (2) Kasalath-specific genes that are located in a large insertion-deletion (INDEL) region that is absent in Nipponbare. Testing these markers in 159 diverse rice accessions confirmed their diagnostic value across genotypes and showed that Pup1 is present in more than 50% of rice accessions adapted to stress-prone environments, whereas it was detected in only about 10% of the analyzed irrigated/lowland varieties. Furthermore, the Pup1 locus was detected in more than 80% of the analyzed drought-tolerant rice breeding lines, suggesting that breeders are unknowingly selecting for Pup1. A hydroponics experiment revealed genotypic differences in the response to P deficiency between upland and irrigated varieties but confirmed that root elongation is independent of Pup1. Contrasting Pup1 near-isogenic lines (NILs) were subsequently grown in two different P-deficient soils and environments. Under the applied aerobic growth conditions, NILs with the Pup1 locus maintained significantly higher grain weight plant−1 under P deprivation in comparison with intolerant sister lines without Pup1. Overall, the data provide evidence that Pup1 has the potential to improve yield in P-deficient and/or drought-prone environments and in diverse genetic backgrounds.

Mutagenesis in crop improvement under the climate change

Abstract: The purpose of mutation induction is to enhance mutation rate in a short duration in developing new plant varieties. The occurrence of spontaneous mutation frequency rate is very low and difficult to use in plant breeding. Traditionally mutations are induced by physical (e.g. gamma radiation) and chemical (e.g. ethylmethane sulfonate) mutagen treatment of both seed and vegetatively propagated crops. Recently high energy ion beams have been used for mutation induction. They induce largely deletion mutants. In International Atomic Energy Agency (IAEA) mutant database, over 3000 officially released mutant varieties have been released worldwide in cereals, ornamental plants, fruits, vegetables, and oil crops. As a result, sustainable food production has been maintained. By in vitro selection, desirable mutants with useful agronomical traits, e.g. abiotic and biotic stress tolerant can be isolated in a short period of time. The genetic fidelity of the regenerated plants is highly desirable for developing new improved plant varieties and a useful as a reliable tool for feeding the ever-growing human population, genomic function especially under climate change and limited arable land.

How does arbuscular mycorrhizal colonization vary with host plant genotype? An example based on maize (Zea mays) germplasms

Abstract: Colonization of plant roots by arbuscular mycorrhizal (AM) fungi is a primary factor determining mycorrhizal associations. This study aimed to investigate the variation in AM colonization among maize genotypes and in response to plant breeding programs. Three types of maize (Zea mays) germplasms composed of 141 inbred lines, 38 hybrids, and 76 landraces were grown in replicated field experiments in Sapporo, Japan, for two cropping years to evaluate the percentage of root length colonized by indigenous AM fungi. The percent colonization varied greatly and continuously among maize genotypes. Inbred lines that originated (released) in particular locations (e.g., Tokachi, Japan) and years (e.g., 1960s) showed significantly larger values than other lines. Inter-location differences were also observed for landraces. The direction of the year-of-release effect on colonization depended on the origin. No significant differences were observed between leaf-blight-disease-resistant near-isogenic inbred lines and their parents. Modern hybrids showed significantly greater values than inbred lines and older landraces. Evaluating numerous, diverse genotypes demonstrated that AM colonization of maize plants varies with germplasm type, origin (country and location), and year of release, and that modern plant breeding programs do not necessarily lead to the suppression of colonization.

Genetic Diversity, Population Structure, and Linkage Disequilibrium in U.S. Elite Winter Wheat

Abstract: Information on genetic diversity and population structure of elite wheat (Triticum aestivum L.) breeding lines promotes effective use of genetic resources. We analyzed 205 elite wheat breeding lines from major winter wheat breeding programs in the USA using 245 markers across the wheat genomes. This collection showed a high level of genetic diversity as refl ected by allele number per locus (7.2) and polymorphism information content (0.54). However, the diversity of U.S. modern wheat appeared to be lower than previously reported diversity levels in worldwide germplasm collections. As expected, this collection was highly structured according to geographic origin and market class with soft and hard wheat clearly separated from each other. Hard wheat accessions were further divided into three subpopulations. Linkage disequilibrium (LD) was primarily distributed around centromere regions. The mean genome-wide LD decay estimate was 10 cM (r 2 > 0.1), although the extent of LD was highly variable throughout the genome. Our results on genetic diversity of different gene pools and the distribution of LD facilitates the effective use of genetic resources for wheat breeding and the choice of marker density in gene mapping and markerassisted breeding.

Difference in response to drought stress among Tibet wild barley genotypes

Abstract: Wild barley germplasms are a treasure trove of useful genes and provide rich sources of genetic variation for crop improvement. We carried out a hydroponic and pot evaluation of diverse germplasms in response to drought stress using 47 Tibet annual wild barley genotypes. Our results from the hydroponic experiment showed that SPAD (soil–plant analyses development analyses, based on chlorophyll meter readings), plant height, and biomass of shoot/root were significantly reduced in plants exposed to drought stress (exposure of plant roots to air for 6 h daily for a period of 7 days) compared with control plants. There were significant differences among the 47 wild barley genotypes in terms of the reduction in these growth parameters, with variation coefficients and diversity indexes ranging from 23.2 to 49.1% and 1.46 to 1.62, respectively, suggesting a rich genetic diversity among the tested accessions. Genotypes XZ5 and XZ150 showed the least reduction, indicating their high tolerance to drought stress, while genotypes XZ54 and XZ147 showed the greatest reduction, and drought stress symptoms appeared rapidly and severely in these latter genotypes. The trends in the different responses of these genotypes to drought stress were fairly consistent in both the hydroponic and the two pot selection experiments, with XZ5 and XZ150 screened as drought-resistant genotypes and XZ54, XZ147 as drought-sensitive ones. Significant genotypic differences in leaf soluble sugar content and water use efficiency in response to drought stress were also observed in pot experiment two, with the drought-tolerant genotype XZ5 showing a markedly higher recovery and the two drought-sensitive genotypes XZ54 and XZ147 showing a markedly lower recovery than the control plants.

Transgene × Environment Interactions in Genetically Modified Wheat

Abstract: Background: The introduction of transgenes into plants may cause unintended phenotypic effects which could have an impact on the plant itself and the environment. Little is published in the scientific literature about the interrelation of environmental factors and possible unintended effects in genetically modified (GM) plants. Methods and Findings: We studied transgenic bread wheat Triticum aestivum lines expressing the wheat Pm3b gene against the fungus powdery mildew Blumeria graminis f.sp. tritici. Four independent offspring pairs, each consisting of a GM line and its corresponding non-GM control line, were grown under different soil nutrient conditions and with and without fungicide treatment in the glasshouse. Furthermore, we performed a field experiment with a similar design to validate our glasshouse results. The transgene increased the resistance to powdery mildew in all environments. However, GM plants reacted sensitive to fungicide spraying in the glasshouse. Without fungicide treatment, in the glasshouse GM lines had increased vegetative biomass and seed number and a twofold yield compared with control lines. In the field these results were reversed. Fertilization generally increased GM/control differences in the glasshouse but not in the field. Two of four GM lines showed up to 56% yield reduction and a 40-fold increase of infection with ergot disease Claviceps purpurea compared with their control lines in the field experiment; one GM line was very similar to its control. Conclusions: Our results demonstrate that, depending on the insertion event, a particular transgene can have large effects on the entire phenotype of a plant and that these effects can sometimes be reversed when plants are moved from the glasshouse to the field. However, it remains unclear which mechanisms underlie these effects and how they may affect concepts in molecular plant breeding and plant evolutionary ecology.

Genetic dissection of nitrogen nutrition in pea through a QTL approach of root, nodule, and shoot variability

Abstract: Pea (Pisum sativum L.) is the third most important grain legume worldwide, and the increasing demand for protein-rich raw material has led to a great interest in this crop as a protein source. Seed yield and protein content in crops are strongly determined by nitrogen (N) nutrition, which in legumes relies on two complementary pathways: absorption by roots of soil mineral nitrogen, and fixation in nodules of atmospheric dinitrogen through the plant–Rhizobium symbiosis. This study assessed the potential of naturally occurring genetic variability of nodulated root structure and functioning traits to improve N nutrition in pea. Glasshouse and field experiments were performed on seven pea genotypes and on the ‘Cameor’ × ‘Ballet’ population of recombinant inbred lines selected on the basis of parental contrast for root and nodule traits. Significant variation was observed for most traits, which were obtained from non-destructive kinetic measurements of nodulated root and shoot in pouches, root and shoot image analysis, 15N quantification, or seed yield and protein content determination. A significant positive relationship was found between nodule establishment and root system growth, both among the seven genotypes and the RIL population. Moreover, several quantitative trait loci for root or nodule traits and seed N accumulation were mapped in similar locations, highlighting the possibility of breeding new pea cultivars with increased root system size, sustained nodule number, and improved N nutrition. The impact on both root or nodule traits and N nutrition of the genomic regions of the major developmental genes Le and Af was also underlined.

Diversity of common bean (Phaseolus vulgaris L.) genotypes in iron and zinc contents under screenhouse conditions.

Abstract: Deficiencies in iron and zinc have health consequences for humans, such as anaemia, poor growth and development in children and low productivity in adults. To guarantee sufficient supply of iron and zinc through diet mainly consisting of staple foods, such as common bean (Phaseolus vulgaris L.), specific interventions in plant breeding are needed. However, seed mineral content has not been a selection criterion for plant breeding, although genetic variation for this trait is present in available germplasm collections. The aim of this study was to evaluate variability of iron and zinc concentrations among common bean genotypes grown in four major bean growing areas in Tanzania for breeding work. Ninety genotypes collected were evaluated under screen house at Sokoine University of Agriculture. A completely randomized design with three replications was used. Seeds and leaves were collected, dried, ground and the powder was used for iron and zinc determination using atomic absorption spectrophotometer. Variation in iron and zinc contents was observed among genotypes both in seeds and leaves and best genotypes identified. Results have shown a positive and significant correlation(r = 0.416; P<0.001) between iron and zinc, suggesting that genetic factors for increasing iron and zinc are co-segregating with genetic factors for increasing zinc. Leaves of the studied varieties have moderate level of zinc (28.0 ppm) and high level of iron (310.0 ppm) forming good source of micronutrients in combating micronutrient malnutrition. Genotypes with high level of iron and zinc should be used as a gene source in future breeding work. Key words: Common bean, iron and zinc.

Identification of quantitative trait loci for specific mechanisms of resistance to Orobanche crenata Forsk. in pea (Pisum sativum L.)

Abstract: Crenate broomrape (Orobanche crenata) is the major constraint for pea cultivation in the Mediterranean Basin and Middle East. Cultivation of resistant varieties would be the most efficient, economical and environmentally friendly way to control this parasite. However, little resistance is available within cultivated pea. Promising sources of resistance have been identified in wild peas but their use in breeding programs is hampered by the polygenic nature of the resistance. The identification of molecular markers linked to the resistance would allow tracking of the underlying genes, facilitating their introgression into pea cultivars. The main objective of this study was the identification of genomic regions associated with resistance to O. crenata. A RIL (Recombinant Inbred Lines) population derived from a cross between a resistant accession of the wild pea Pisum sativum ssp. syriacum, and a susceptible pea variety was screened for resistance to O. crenata under field conditions during two seasons. In addition, resistance reactions at different stages of the O. crenata infection cycle were assessed using a Petri dish method. The approach allowed the identification of four Quantitative Trait Loci (QTL) associated with field resistance, assessed as the number of emerged broomrape shoots per pea plant under field conditions. These identified QTLs explained individually from 10 to 17% of the phenotypic variation. In addition QTLs governing specific mechanisms of resistance, such as low induction of O. crenata seed germination, lower number of established tubercles per host root length unit, and slower development of tubercles were also identified. Identified QTLs explained individually from 8 to 37% of the variation observed depending on the trait. Host plant aerial biomass and root length were also assessed and mapped. Both traits were correlated with the level of O. crenata infection and three out of the four QTLs controlling resistance under field conditions co-localized with QTLs controlling plant aerial biomass or root length. The relationship observed among these traits and resistance is discussed.

Breeding spring wheat for improved allelopathic potential

Abstract: Bertholdsson N-O (2010). Breeding spring wheat for improved allelopathic potential. Weed Research50, 49–57. Summary It is becoming apparent that allelopathy plays a significant role in the competitive ability of cereals against weeds; barley, wheat and rice cultivars with high allelopathic activity have been identified. However, direct breeding efforts to improve allelopathy have to date only been reported in rice. In this study, a breeding programme in spring wheat (Triticum aestivum) was evaluated to determine the efficiency of selection of allelopathy and the ability of breeding lines to suppress weeds in the field. The material used originated from a cross between a Swedish cultivar with low allelopathic activity and a Tunisian cultivar with high allelopathic activity. Allelopathic activity was measured as growth inhibition of perennial ryegrass (Lolium perenne) roots when grown together with the wheat cultivars on agar. For screening of F2 populations, a single plant bioassay was used for the first time. In the F6 and F7 generations, three breeding lines with an average improved allelopathy of 20% and one line with an unimproved allelopathy activity, but with the same phenotype as the high allelopathic lines, were tested together with the low allelopathic Swedish parent. The main result from the field study was a 19% average reduction of weed biomass for the high allelopathic lines, but no significant reduction of the low allelopathic breeding line. Early shoot length and early crop biomass (stages 37–39, Zadoks scale) and straw length of the high allelopathic lines were not significantly different from the Swedish parent. A negative effect was that grain yield was reduced by 9% in the high allelopathic lines. It is suggested that the reduced biomass of weeds in plots planted with the highly allelopathic wheat lines is related to differences in allelopathic activity and not differences in plant growth.

Detection of somaclonal variants in somatic embryogenesis-regenerated plants of Vitis vinifera by flow cytometry and microsatellite markers

Abstract: Flow cytometry and microsatellite analyses were used to evaluate the trueness-to-type of somatic embryogenesis-regenerated plants from six important Spanish grapevine (Vitis vinifera L) cultivars Tetraploid plants were regenerated through somatic embryogenesis from all of the cultivars tested with the exception of ‘Merenzao’ In addition, an octoploid plant was obtained in the cv ‘Albarino’, and two mixoploids in ‘Torrontes’ The most probable origin of these ploidy variations is somaclonal variation The cv ‘Brancellao’ presented significantly more polyploids (2857%) than any other cultivar, but it must be noted that 50% of the adult field-grown ‘Brancellao’ mother plants analysed were mixoploid Hence, it is probable that these polyploids originated either from somaclonal variation or by separation of genotypically different cell layers through somatic embryogenesis Microsatellite analysis of somatic embryogenesis-regenerated plants showed true-to-type varietal genotypes for all plants except six ‘Torrontes’ plants, which showed a mutant allele (231) instead of the normal one (237) at the locus VVMD5 There was not a clear relationship between the occurrence of the observed mutant regenerated plants and the callus induction media composition, the developmental stage of the inflorescences, the type of explant used for starting the cultures or the type of germination (precocious in differentiation medium or normal in germination medium) in any of the cultivars tested, except ‘Torrontes’ The mutant plants described herein have been transplanted to soil for future evaluation of putative phenotypic traits of interest These mutants can be useful both for breeding programs and for functional genomic approaches aimed at increasing knowledge of the biology of grapevine

Mapping QTLs for nitrogen-deficiency tolerance at seedling stage in rice (Oryza sativa L.).

Abstract: With 2 figures and 4 tables Abstract A recombinant inbred line (RIL) population, consisting of 238 F12 lines derived from ‘R9308’/’Xieqingzao B’, the parents of a super hybrid rice in China, was developed for mapping quantitative trait locus (QTL) for nitrogen deficiency tolerance. A genetic linkage map with 198 simple sequence repeat (SSR) markers was constructed. Six traits of shoot dry weight (SW), root dry weight (RW), plant dry weight (PW), maximum root length (RL), chlorophyll content (Chl), plant height (PH) were used to assess the N-deficiency tolerance. The ratio of the parameters from the two treatments was calculated as derived parameters. QTL analysis detected seven QTLs on chromosomes 1, 2, 3 and 8 associated with N-deficiency tolerance in this mapping population. These QTLs explained 9.07–14.45% of the phenotypic variation. The ‘R9308’ alleles increased the relative traits except that of locus on chromosome 8. One of the major QTL clusters was detected in the interval RM5385–RM7192 on chromosome 1, which was associated with N recycling in rice. This chromosomal region may be enriched with the key N metabolism genes.

Hybrid Breeding in Durum Wheat: Heterosis and Combining Ability

Abstract: Hybrid breeding facilitates a maximum exploitation of heterosis. The objectives of our research were to (i) examine the magnitude of heterosis over the mid- and better parent for yield, yield components, and quality traits in Central European spring durum wheat and (ii) investigate the efficiency of parental selection based on mid-parent value or general combining ability effects. Sixteen inbred lines and 40 incomplete factorial crosses were field-evaluated for eight agronomic traits at 10 environments in Germany. For grain yield, the hybrids yielded on average 10% higher than the mid-parent performance, and the maximum superiority was 22%. The significantly positive contrast between inbreeding depression and mid-parent heterosis for grain yield indicated the presence of positive additive x additive epistatic interactions. Furthermore, the best hybrid outperformed the best line variety by 1.01 Mg ha ―1 . We conclude that there is a potential for hybrid breeding in durum wheat.