Showing papers by "Institut national de la recherche agronomique published in 1994"

Photooxidative stress in plants

Abstract: The light-dependent generation of active oxygen species is termed photooxidative stress. This can occur in two ways: (1) the donation of energy or electrons directly to oxygen as a result of photosynthetic activity; (2) exposure of tissues to ultraviolet irradiation. The light-dependent destruction of catalase compounds the problem. Although generally detrimental to metabolism, superoxide and hydrogen peroxide may serve useful functions if rigorously controlled and compartmentalised. During photosynthesis the formation of active oxygen species is minimised by a number of complex and refined regulatory mechanisms. When produced, active oxygen species are eliminated rapidly by efficient antioxidative systems. The chloroplast is able to use the production and destruction of hydrogen peroxide to regulate the thermal dissipation of excess excitation energy. This is an intrinsic feature of the regulation of photosynthetic electron transport. Photoinhibition and photooxidation only usually occur when plants are exposed to stress. Active oxygen species are part of the alarm-signalling processes in plants. These serve to modify metabolism and gene expression so that the plant can respond to adverse environmental conditions, invading organisms and ultraviolet irradiation. The capacity of the antioxidative defense system is often increased at such times but if the response is not sufficient, radical production will exceed scavenging and ultimately lead to the disruption of metabolism. Oxidative damage arises in high light principally when the latter is in synergy with additional stress factors such as chilling temperatures or pollution. Environmental stress can modify the photooxidative processes in various ways ranging from direct involvement in light-induced free radical formation to the inhibition of metabolism that renders previously optimal light levels excessive. It is in just such situations that the capacity for the production of active oxygen species can exceed that for scavenging by the antioxidative defense systems. The advent of plant transformation, however, may have placed within our grasp the possibility of engineering greater stress tolerance in plants by enhancement of the antioxidative defence system.

The microbiology of minimally processed fresh fruits and vegetables

Abstract: Minimally processed fresh (MPF) fruits and vegetables are good media for growth of microorganisms. They have been involved in outbreaks because of the consumption of products contaminated by pathogens. They are also sensitive to various spoilage microorganisms such as pectinolytic bacteria, saprophytic Gram-negative bacteria, lactic acid bacteria, and yeasts. Contamination of MPF fruits and vegetables occurs at every stage of the food chain, from cultivation to processing. Polluted environments during cultivation or poor hygienic conditions in processing increase the risk of contamination with foodborne pathogens. Although MPF fruits and vegetables may harbor psychrotrophic microorganisms such as fluorescent pseudomonads or Listeria monocytogenes, good control of refrigeration temperature limits growth of spoilage and pathogenic microorganisms. Modified atmospheres are often efficient to maintain or improve visual organoleptic quality of MPF fruits and vegetables, but their effects on microorganisms are inconsistent. Chemical disinfection can partially reduce the initial bacterial contamination; irradiation seems to be more efficient. The applications of legislations and quality assurance systems to control contamination, survival, and growth of foodborne pathogens in MPF fruits and vegetables are discussed.

Tansley Review No. 76 Helper bacteria: a new dimension to the mycorrhizal symbiosis

Abstract: SUMMARY The symbiotic establishment of mycorrhizal fungi on plant roots is affected in various ways by the other microorganisms of the rhizosphere, and more especially by bacteria. This review discusses the case of some of these bacteria which consistently promote mycorrhizal development, leading to the concept of 'mycorrhization' helper bacteria (MHBs). Examples of MHB evidence are given from the literature, with special reference to the Douglas fir (Pseudotsuga menzeisii Mirb. Franco)-Laccaria laccata Scop. ex Fr. ectomycorrhizal combination which has been more extensively studied. The fungal specificity of some MHBs and the various mechanisms underlying their effect are discussed, considering five hypotheses: effects on the receptivity of the root, effects on the root-fungus recognition, effects on the fungal growth, modification of the rhizospheric soil, and effects on the germination of the fungal propagule. MHBs are then considered for their ecological and evolutionary implications, and examples of practical applications in forest nurseries are given: when added to the fungal inoculum, MHBs can improve the success of ectomycorrhizal inoculation of planting stocks with fungi selected for their outstanding growth stimulation after outplanting. The conclusion points out a number of fundamental questions which remain unanswered about mycorrhization helper bacteria and suggests some investigation priorities in this new field of mycorrhiza research.

Mapping Quantitative Trait Loci in Crosses between Outbred Lines Using Least Squares

Abstract: The use of genetic maps based upon molecular markers has allowed the dissection of some of the factors underlying quantitative variation in crosses between inbred lines. For many species crossing inbred lines is not a practical proposition, although crosses between genetically very different outbred lines are possible. Here we develop a least squares method for the analysis of crosses between outbred lines which simultaneously uses information from multiple linked markers. The method is suitable for crosses where the lines may be segregating at marker loci but can be assumed to be fixed for alternative alleles at the major quantitative trait loci (QTLs) affecting the traits under analysis (e.g., crosses between divergent selection lines or breeds with different selection histories). The simultaneous use of multiple markers from a linkage group increases the sensitivity of the test statistic, and thus the power for the detection of QTLs, compared to the use of single markers or markers flanking an interval. The gain is greater for more closely spaced markers and for markers of lower information content. Use of multiple markers can also remove the bias in the estimated position and effect of a QTL which may result when different markers in a linkage group vary in their heterozygosity in the F1 (and thus in their information content) and are considered only singly or a pair at a time. The method is relatively simple to apply so that more complex models can be fitted than is currently possible by maximum likelihood. Thus fixed effects of background genotype can be fitted simultaneously with the exploration of a single linkage group which will increase the power to detect QTLs by reducing the residual variance. More complex models with several QTLs in the same linkage group and two-locus interactions between QTLs can similarly be examined. Thus least squares provides a powerful tool to extend the range of crosses from which QTLs can be dissected whilst at the same time allowing flexible and realistic models to be explored.

Enzymatic browning reactions in apple and apple products

Abstract: This review examines the parameters of enzymatic browning in apple and apple products that is, phenolic compounds, polyphenoloxidases, and other factors (ascorbic acid and peroxidases), both qualitatively and quantitatively. Then the relationships between intensity of browning and the browning parameters are discussed, including a paragraph on the methods used for browning evaluation. Finally, the different methods for the control of browning are presented.

The phloem-limited bacterium of greening disease of citrus is a member of the α subdivision of the Proteobacteria

Abstract: Using the PCR, we amplified the 16S ribosomal DNAs (rDNAs) of an Asian strain and an African strain of the uncultured, gram-negative, walled, phloem-limited bacterium-like organism (BLO) associated with citrus greening disease. We evaded coamplification of chloroplast 16S rDNA by using restriction enzymes; the chloroplast 16S rDNA was sensitive to Bcl I digestion and resistant to Eco RI digestion, while the 16S rDNA of the BLO was resistant to Bcl I digestion and sensitive to Eco RI digestion. The 16S rDNA of the African BLO strain was amplified from Bcl I-digested DNA extracted from infected periwinkle leaf midribs. The Asian strain was isolated from plant extract by using a specific monoclonal antibody coated onto the surface of a PCR tube. The 16S rDNAs of the two BLO strains were cloned and sequenced. Comparisons with sequences of 16S rDNAs obtained from the GenBank data base revealed that the two citrus greening disease BLOs belong to the alpha subdivision of the class Proteobacteria. Even though their closest relatives are members of the alpha-2 subgroup, these BLOs are distinct from this subgroup as we observed only 87.5% homology between the 16S rDNAs examined. Therefore, the two BLOs which we studied probably are members of a new lineage in the α subdivision of the Proteobacteria. We propose the trivial name “liberobacter” for this new group of bacteria and will wait until additional characteristics have been determined before we propose a formal name.

Prediction of net energy value of feeds for growing pigs

Abstract: Digestible (DE), metabolizable (ME), and net (NE) energy values of 61 diets were measured in 45-kg growing Large White boars. Net energy was calculated as energy retained at an average ME intake equivalent to 540 kcal/kg BW.60 plus fasting heat production estimated from data of the present experiment as 179 kcal/kg BW.60. Retained energy was measured as the difference between ME intake and heat production obtained in respiration chambers. The amounts of DE digested before the end of the ileum (DEi) and in the hindgut (DEh) were also measured for each diet. Regression equations for predicting dietary NE content from digestible nutrient levels or from DE or ME and chemical characteristics or from chemical composition only were calculated. Efficiencies of utilization of ME for NE (k, %) were also obtained. The mean k value for the 61 diets was 74% (range: 69 to 77). Digestible nutrients were used differently for NE: k values varied from approximately 60% for digestible CP or digestible cell wall fractions to 82% for starch and 90% for digestible ether extract. Accordingly, k for ME associated with DEh was lower than ME from DEi (58 vs 76%). Equations for predicting NE content are proposed. Their applicability, the comparison with other available NE prediction equations, and the effects of energy system on diet formulation are discussed.

Rapid Identification of Rhizobia by Restriction Fragment Length Polymorphism Analysis of PCR-Amplified 16S rRNA Genes.

Abstract: Forty-eight strains representing the eight recognized Rhizobium species, two new Phaseolus bean Rhizobium genomic species, Bradyrhizobium spp., Agrobacterium spp., and unclassified rhizobia from various host plants were examined by restriction fragment length polymorphism (RFLP) analysis of 16S rRNA genes amplified by polymerase chain reaction (PCR). Twenty-one composite genotypes were obtained from the combined data of the RFLP analysis with nine endonucleases. Species assignments were in full agreement with the established taxonomic classification. Estimation from these data of genetic relationships between and within genera and species correlated well with previously published data based on DNA-rRNA hybridizations and sequence analysis of 16S rRNA genes. This PCR-RFLP method provides a rapid tool for the identification of root nodule isolates and the detection of new taxa. Images

Resistance-associated point mutations in insecticide-insensitive acetylcholinesterase

Abstract: Extensive utilization of pesticides against insects provides us with a good model for studying the adaptation of a eukaryotic genome to a strong selective pressure. One mechanism of resistance is the alteration of acetylcholinesterase (EC 3.1.1.7), the molecular target for organophosphates and carbamates. Here, we report the sequence analysis of the Ace gene in several resistant field strains of Drosophila melanogaster. This analysis resulted in the identification of five point mutations associated with reduced sensitivities to insecticides. In some cases, several of these mutations were found to be combined in the same protein, leading to different resistance patterns. Our results suggest that recombination between resistant alleles preexisting in natural populations is a mechanism by which insects rapidly adapt to new selective pressures.

Triticum aestivum puroindolines, two basic cystine-rich seed proteins: cDNA sequence analysis and developmental gene expression.

Abstract: From a mid-maturation seed cDNA library we have isolated cDNA clones encoding two Triticum aestivum puroindolines. Puroindoline-a and puroindoline-b, which are 55% similar, are basic, cystine-rich and tryptophan-rich proteins. Puroindolines are synthezised as preproproteins which include N- and C-terminal propeptides which could be involved in their vacuolar localization. The mature proteins have a molecular mass of 13 kDa and a calculated isoelectric point greater than 10. A notable feature of the primary structure of puroindolines is the presence of a tryptophan-rich domain which also contains basic residues. A similar tryptophan-rich domain was found within an oat seed protein and a mammalian antimicrobial peptide. The ten cysteine residues of puroindolines are organized in a cysteine skeleton which shows similarity to the cysteine skeleton of other wheat seed cystine-rich proteins. Northern blot analysis showed that puroindoline genes are specifically expressed in T. aestivum developing seeds. No puroindoline transcripts as well as no related genes were detected in Triticum durum. The identity of puroindolines to wheat starch-granule associated proteins is discussed as well as the potential role of puroindolines in the plant defence mechanism.

Interactions between mycorrhizal fungi and other soil organisms

Abstract: Mycorrhizal fungi interact with a wide range of other soil organisms, in the root, in the rhizosphere and in the bulk soil. These interactions may be inhibitory or stimulatory; some are clearly competitive, others may be mutualistic. Effects can be seen at all stages of the mycorrhizal fungal life-cycle, from spore population dynamics (predation, dispersal and germination) through root colonization to external hyphal growth. Two areas that seem likely to be of particular importance to the functioning of the symbiosis are the role of bacteria in promoting mycorrhiza formation and of soil animals in grazing the external mycelium. Mycorrhizal fungi also modify the interactions of plants with other soil organisms, both pathogens, such as root-inhabiting nematodes and fungi, and mutualists, notably nitrogen-fixing bacteria. These interactions are probably important both in natural ecosystems, where pathogens are increasingly recognized as playing controlling roles, and in agricultural systems, where mycorrhizas may be valuable in designing integrated systems of pest control and growth stimulation.

Manipulation of lignin quality by downregulation of cinnamyl alcohol dehydrogenase

Abstract: The composition of lignin in tobacco stems has been altered by genetic engineering. Antisense expression of sequences encoding cinnamyl alcohol dehydrogenase (CAD), the enzyme catalysing the final step in lignin precursor synthesis, leads to the production of a modified lignin in otherwise normal plants. Although Klason and acetyl bromide lignin determinations show little quantitative change in lignin deposition in CAD antisense plants, a number of qualitative changes have been identified. The lignin is altered in both composition and structure and is more susceptible to chemical extraction. Consistent with a block in CAD activity, antisense plants incorporate less cinnamyl alcohol monomers and more cinnamyl aidehyde monomers into lignin than corresponding control plants. Antisense plants with very low levels of CAD activity also show a novel phenotype with the appearance of a red-brown colour in xylem tissues. A similar phenotype is correlated with altered lignification and improved digestibility in brownmidrib mutants of maize and sorghum. The improved chemical extractability of lignin in CAD antisense plants supports a role for this technology in improving the pulp and paper-making value of forest trees while the similarity with brown-midrib mutants suggests a route to more digestible forage crops.

A set of 99 cattle microsatellites: characterization, synteny mapping, and polymorphism

Abstract: Cattle microsatellite clones (136) were isolated from cosmid (10) and plasmid (126) libraries and sequenced. The dinucleotide repeats were studied in each of these sequences and compared with dinucleotide repeats found in other vertebrate species where information was available. The distribution in cattle was similar to that described for other mammals, such as rat, mouse, pig, or human. A major difference resides in the number of sequences present in the bovine genome, which seemed at best one-third as large as in other species. Oligonucleotide primers (117 pairs) were synthesized, and a PCR product of expected size was obtained for 88 microsatellite sequences (75%). Synteny or chromosome assignment was searched for each locus with PCR amplification on a panel of 36 hamster/bovine somatic cell hybrids. Of our bovine microsatellites, eighty-six could be assigned to synteny groups of chromosomes. In addition, 10 other microsatellites—HEL 5, 6, 9, 11, 12, 13 (Kaukinen and Varvio 1993), HEL 4, 7, 14, 15—as well as the microsatellite found in the κ-casein gene (Fries et al. 1990) were mapped on the hybrids. Microsatellite polymorphism was checked on at leat 30 unrelated animals of different breeds. Almost all the autosomal and X Chr microsatellites displayed polymorphism, with the number of alleles varying between two and 44. We assume that these microsatellites could be very helpful in the construction of a primary public linkage map of the bovine genome, with an aim of finding markers for Economic Trait Loci (ETL) in cattle.

A wind tunnel study of air flow in waving wheat: Two-point velocity statistics

Abstract: We analyse single-point velocity statistics obtained in a wind tunnel within and above a model of a waving wheat crop, consisting of nylon stalks 47 mm high and 0.25 mm wide in a square array with frontal area index 0.47. The variability of turbulence measurements in the wind tunnel is illustrated by using a set of 71 vertical traverses made in different locations, all in the horizontally-homogeneous (above-canopy) part of the boundary layer. Ensemble-averaged profiles of the statistical moments up to the fourth order and profiles of Eulerian length scales are presented and discussed. They are consistent with other similar experiments and reveal the existence of large-scale turbulent coherent structures in the flow. The drag coefficient in this canopy as well as in other reported experiments is shown to exhibit a characteristic height-dependency, for which we propose an interpretation. The velocity spectra are analysed in detail; within and just above the canopy, a scaling based on fixed length and velocity scales (canopy height and mean horizontal wind speed at canopy top) is proposed. Examination of the turbulent kinetic energy and shear stress budgets confirms the role of turbulent transport in the region around the canopy top, and indicates that pressure transport may be significant in both cases. The results obtained here show that near the top of the canopy, the turbulence properties are more reminiscent of a plane mixing layer than a wall boundary layer.

Chronic dietary α-linolenic acid deficiency alters dopaminergic and serotoninergic neurotransmission in rats

Abstract: This study examined the effects of dietary alpha-linolenic acid [18:3(n-3)] deficiency on dopaminergic serotoninergic neurotransmission systems in 60-d-old male rats. Rats were fed semipurified diets containing either peanut oil [the (n-3)-deficient group] or peanut plus rapeseed oil (control group). We measured the densities of the serotonin-2 (5-HT2) receptors and the dopamine-2 (D2) receptors by autoradiography and membrane-binding assays in relation to the fatty acid composition and levels of endogenous monoamines in three cerebral regions: the frontal cortex, the striatum and the cerebellum. Long-term feeding of the (n-3)-deficient diet induced a significantly higher 5-HT2 receptor density in the frontal cortex compared with the control rats without any difference in the endogenous serotonin concentrations. The results also showed some modification of dopaminergic neurotransmission specifically in the frontal cortex in the rats deficient in alpha-linolenic acid, with a significantly lower density of D2 receptors and a significantly lower concentration of endogenous dopamine than in control animals. Moreover, there were lower levels of (n-3) fatty acids in all the regions studied in the deficient rats, balanced by greater levels of (n-6) fatty acids. These results suggest that chronic consumption of an alpha-linolenic acid-deficient diet could induce modifications of the neurotransmission pathways; this might induce the behavioral disturbances previously described in this fatty acid-deficient animal model.

Dynamics of the calcium signal that triggers mammalian egg activation.

Abstract: Publisher Summary At fertilization in mammals, the incoming sperm makes two essential contributions to the development of the new organism. One contribution is the DNA and all its associated genes, which enables a diploid organism to develop to full term. The other is the message that triggers egg development. Without this message, delivering the DNA is pointless. In all animal species studied, the message that the sperm delivers is written in the language of cell Ca2+ changes. This chapter focuses on the way that changes of intracellular Ca2+ are generated in mammalian eggs, and describes how these Ca2+ changes affect the subsequent development of the embryo. It is shown that the Ca2+ dynamics at fertilization in mammalian eggs are more complex than in nonmammalian systems. One of the main points that is emphasized is that mammalian eggs are different from other eggs in that they undergo Ca2+ oscillations, or repetitive Ca2+ spikes, during activation at fertilization. One of the central problems to be solved is the triggering mechanism for the oscillations at fertilization. Ca2+o scillations have been described in a vast range of somatic cell types.

Ozone, Sulfur Dioxide, and Ultraviolet B Have Similar Effects on mRNA Accumulation of Antioxidant Genes in Nicotiana plumbaginifolia L

Abstract: We have studied the expression of antioxidant genes in response to near ambient conditions of O3, SO2, and ultraviolet B (UV-B) in Nicotiana plumbaginifolia L. The genes analyzed encode four different superoxide dismutases (SODs), three catalases (Cat1, Cat2, and Cat3), the cytosolic ascorbate peroxidase (cyt APx), and glutathione peroxidase (GPx). The experimental setup for each treatment was essentially the same and caused no visible damage, thus allowing direct comparison of the different stress responses. Our data showed that the effects of O3, SO2, and UV-B on the antioxidant genes are very similar, although the response to SO2 is generally less pronounced and delayed. The effects of the different stresses are characterized by a decline in Cat1, a moderate increase in Cat3, and a strong increase in Cat2 and GPx. Remarkably, SODs and cyt APx were not affected. Analysis of SOD and APx expression in the ozone-sensitive Nicotiana tabacum L. cv PBD6 revealed that induction of the cytosolic copper/zinc SOD and cyt APx occurs only with the onset of visible damage. It is proposed that alterations in mRNA levels of catalases and GPx, but not of SODs and cyt APx, form part of the initial antioxidant response to O3, SO2, and UV-B in Nicotiana.

A mimicked in-situ remediation study of metal-contaminated soils with emphasis on cadmium and lead

Abstract: The capacity of several additives, i.e., lime, Thomas phosphate baric slag (TBS), hydrous iron oxides (HFO), hydrous manganese oxides (HMO), and Beringite, added to soil to Fix Cd or Pb, was evaluated using two pot experiments in tandem with soil extractions. Three soils from France with metal contents ranging from 0.17 to 108 mg Cd kg -1 soil dry weight (DW) and 47 to 1112 mg Pb kg -1 soil DW were studied. Metal sources were: sludge-borne metals (Soil A), fallout from a smelter (Soil B), and emission from a tetraethyl Pb production facility (Soil C). Ryegrass (Lolium spp.) or tobacco (Nicotiana tabacum L.) shoots were harvested

Carbon Source Requirements for Exopolysaccharide Production by Lactobacillus casei CG11 and Partial Structure Analysis of the Polymer.

Abstract: Exopolysaccharide production by Lactobacillus casei CG11 was studied in basal minimum medium containing various carbon sources (galactose, glucose, lactose, sucrose, maltose, melibiose) at concentrations of 2, 5, 10, and 20 g/liter. L. casei CG11 produced exopolysaccharides in basal minimum medium containing each of the sugars tested; lactose and galactose were the poorest carbon sources, and glucose was by far the most efficient carbon source. Sugar concentrations had a marked effect on polymer yield. Plasmid-cured Muc- derivatives grew better in the presence of glucose and attained slightly higher populations than the wild-type strain. The values obtained with lactose were considerably lower for both growth and exopolysaccharide yield. The level of specific polymer production per cell obtained with glucose was distinctively lower for Muc- derivatives than for the Muc+ strain. The polymer produced by L. casei CG11 in the presence of glucose was different from that formed in the presence of lactose. The polysaccharide produced by L. casei CG11 in basal minimum medium containing 20 g of glucose per liter had an intrinsic viscosity of 1.13 dl/g. It was rich in glucose (76%), which was present mostly as 2- or 3-linked residues along with some 2,3 doubly substituted glucose units, and in rhamnose (21%), which was present as 2-linked or terminal rhamnose; traces of mannose and galactose were also present.

Elevated Levels of Superoxide Dismutase Protect Transgenic Plants Against Ozone Damage

Abstract: To evaluate the feasibility of using engineered antioxidant enzymes as an approach to improve the tolerance of plants to ambient stress, we have constructed transgenlc tobacco plants that overproduce superoxide dismutase (SOD), an enzyme which converts superoxide radicals into hydrogen peroxide and oxygen, and is believed to play a crucial role in antioxidant defense. We have targeted the MnSOD from Nicotiana plumbaginifolia either to the chloroplasts or to the mitochondria, and evaluated the ozone tolerance of transgenic and control plants. Enhanced SOD activity in the mitochondria had only a minor effect on ozone tolerance. However, overproduction of SOD in the chloroplasts resulted in a 3–4 fold reduction of visible ozone injury.

Characterization of edible oils, butters and margarines by Fourier transform infrared spectroscopy with attenuated total reflectance

Abstract: The combination of attenuated total reflectance (ATR) and mid-infrared spectroscopy (MIRS) with statistical multidimensional techniques made it possible to extract relevant information from MIR spectra of lipid-rich food products. Wavenumber assignments for typical functional groups in fatty acids were made for standard fatty acids: Absorption bands around 1745 cm−1, 2853 cm−1, 2954 cm−1, 3005 cm−1, 966 cm−1, 3450 cm−1 and 1640 cm−1 are due to absorption of the carbonyl group, C−H stretch, =CH double bonds of lipids and O−H of lipids, respectively. In lipid-rich food products, some bands are modified. Water strongly absorbs in the region of 3600–3000 cm−1 and at 1650 cm−1 in butters and margarines, allowing one to rapidly differentiate the foods as function of their water content. Principal component analysis was used to emphasize the differences between spectra and to rapidly classify 27 commercial samples of oils, butters and margarines. As the MIR spectra contain information about carbonyl groups and double bonds, the foods were classified with ATR-MIR, in agreement with their degree of esterification and their degree of unsaturation as determined from gas-liquid chromatography analysis. However, it was difficult to differentiate the studied food products in terms of their average chainlength.

Molecular genetics of growth and development in Populus. III. A genetic linkage map of a hybrid poplar composed of RFLP, STS, and RAPD markers.

Abstract: We have evaluated three DNA-based marker types for linkage map construction in Populus: RFLPs detected by Southern blot hybridization, STSs detected by a combination of PCR and RFLP analysis, and RAPDs. The mapping pedigree consists of three generations, with the F1 produced by interspecific hybridization between a P. trichocarpa female and a P. deltoides male. The F2 generation was made by inbreeding to the maximum degree permitted by the dioecious mating system of Populus. The applicability of STSs and RAPDs outside the mapping pedigree has been investigated, showing that these PCR-based marker systems are well-suited to breeding designs involving interspecific hybridization. A Populus genome map (343 markers) has been constructed from a combination of all three types. The length of the Populus genome is estimated to be 2400–2800 cM.