Nigra Cv Research Articles

High-resolution methylome analysis uncovers stress-responsive genomic hotspots and drought-sensitive transposable element superfamilies in the clonal Lombardy poplar.

DNA methylation is environment-sensitive and can mediate stress responses. In trees, changes in the environment might cumulatively shape the methylome landscape over time. However, because high-resolution methylome studies usually focus on single environmental cues, the stress-specificity and long-term stability of methylation responses remain unclear. Here, we studied the methylome plasticity of a Populus nigra cv. 'Italica' clone widely distributed across Europe. Adult trees from different geographic locations were clonally propagated in a common garden experiment and exposed to cold, heat, drought, herbivory, rust infection, and salicylic acid treatments. Whole-genome bisulfite sequencing revealed stress-induced and naturally occurring DNA methylation variants. In CG/CHG contexts, the same genomic regions were often affected by multiple stresses, suggesting a generic methylome response. Moreover, these variants showed striking overlap with naturally occurring methylation variants between trees from different locations. Drought treatment triggered CHH hypermethylation of transposable elements, affecting entire superfamilies near drought-responsive genes. Thus, we revealed genomic hotspots of methylation change that are not stress-specific and that contribute to natural DNA methylation variation, and identified stress-specific hypermethylation of entire transposon superfamilies with possible functional consequences. Our results underscore the importance of studying multiple stressors in a single experiment for recognizing general versus stress-specific methylome responses.

Herbivory induced methylation changes in the Lombardy poplar: A comparison of results obtained by epiGBS and WGBS.

DNA cytosine methylation is an epigenetic mechanism involved in regulation of plant responses to biotic and abiotic stress and its ability to change can vary with the sequence context in which a cytosine appears (CpG, CHG, CHH, where H = Adenine, Thymine, Cytosine). Quantification of DNA methylation in model plant species is frequently addressed by Whole Genome Bisulfite Sequencing (WGBS), which requires a good-quality reference genome. Reduced Representation Bisulfite Sequencing (RRBS) is a cost-effective potential alternative for ecological research with limited genomic resources and large experimental designs. In this study, we provide for the first time a comprehensive comparison between the outputs of RRBS and WGBS to characterize DNA methylation changes in response to a given environmental factor. In particular, we used epiGBS (recently optimized RRBS) and WGBS to assess global and sequence-specific differential methylation after insect and artificial herbivory in clones of Populus nigra cv. 'italica'. We found that, after any of the two herbivory treatments, global methylation percentage increased in CHH, and the shift was detected as statistically significant only by epiGBS. As regards to loci-specific differential methylation induced by herbivory (cytosines in epiGBS and regions in WGBS), both techniques indicated the specificity of the response elicited by insect and artificial herbivory, together with higher frequency of hypo-methylation in CpG and hyper-methylation in CHH. Methylation changes were mainly found in gene bodies and intergenic regions when present at CpG and CHG and in transposable elements and intergenic regions at CHH context. Thus, epiGBS succeeded to characterize global, genome-wide methylation changes in response to herbivory in the Lombardy poplar. Our results support that epiGBS could be particularly useful in large experimental designs aimed to explore epigenetic changes of non-model plant species in response to multiple environmental factors.

Effects of Melatonin on Morus nigra cv. 'Ekşi Kara' Exposed to Drought Stress

Today, drought stress threatens the world seriously. Determining the effects of some exogenous stimulators in acquiring resistance against stress will contribute to agriculture under drought stress. In this regard, we investigated the effects of melatonin (MEL) on Morus nigra cv. 'Eksi Kara' (black mulberry) in challenging drought. To reach this object, we reproduced 'Eksi Kara', which is registered in Turkey and has economic importance, in tissue culture by using the meristem culture method. Plants were then transferred in a medium containing polyethylene glycol (PEG) 8000, which causes -1.5 MPa drought stress, and 20 μl MEL has applied. Leaf samples were taken on the 5th, 10th, and 15th days after treatments in groups of plants grown in a different medium (Control, Control+MEL, PEG and PEG+MEL). The changes in the pigment system, relative water content (RWC) and antioxidant system were evaluated comparatively between the groups to assess plants' growth and determine their roles in coping with stress. Our findings showed that RWC decreased in leaves under drought. Exogenous MEL added in MS medium had a mitigation effect on stress. The reduction was detected in the chlorophyll and carotenoid content of leaves. Moreover, MEL+PEG combination improved the chlorophyll level. It was seen that exogenous MEL application promoted the plant defence mechanism of M. nigra plants, which exposed to drought stress, by increasing the accumulation of non-enzymatic antioxidants; total glutathione (GSH), total phenolic, proline) and activities of antioxidant enzymes; catalase (CAT), superoxide dismutase (SOD), Glutathione-S-transferase (GST), glutathione reductase (GR), peroxidase (POD), ascorbate peroxidase (APX). This study also indicates that the application of MEL+PEG composition partially prevented membrane lipid peroxidation by decreasing (malondialdehyde) MDA content.

Morphological, phytochemical and biological studies of Morus L. (Moraceae)

Morus L., a multipurpose agro-forestry plant, belongs to tribe Moreae (family Moraceae), has high economical and medicinal values. There are a lot of conflictions regarding the number of Morus spp. as a result of producing new varieties and hybrid individuals. Macro & micromorphological characters viz. whole plant, ab- & adaxial lamina epidermis using SEM, lamina & petiole anatomy, phytochemical screening and quantitative analysis of the polyphenol and flavonoid contents of seven Morus taxa were investigated as well as the survey of polyphenols and flavonoids qualitatively in M. alba, M. macroura and M. nigra using HPLC analysis. The biological studies carried on one selected taxon M. alba (as it is the most prominent of these species). The specific objective of the present study is to throw light on the morpho-anatomical characters of Morus spp. in delamination among them, to screen the phytochemical constituents of aerial parts and fruits as well as to study the in vitro anti-oxidant, cytotoxicity and anti-inflammatory activities of M. alba. The obtained results highlighted that the macro & micromorphological characters were considered diagnostic at specific level viz. fruit size and color, lamina size, shape, margin, apex, base and leaf type, outline of petiole, ground system, aspect and number of vascular bundles, crystals types and phytoliths’ shapes and sizes. The results of UV spectrophotometric analysis indicated that M. nigra cv. Al-taify had the highest content of flavonoids and polyphenols. The polar extract of M. alba showed potential inhibitory effect of induced inflammation and considerable effect on scavenging of free radicals and showed mild growth inhibition of cancer cell lines.

Sustainability of Impacts of Poplar Growth on Soil Organic Matter in Eutric Cambisols

Short rotation coppices (SRC) with poplar on arable soils constitute no-till management in combination with a changed litter quality compared to annual crops. Both tillage and litter quality impact soil organic matter (SOM) composition, but little is known on the sustainability of this impact at the molecular level. We compared the microbial colonization and SOM quantity and quality of a young (4 years), old (17 years) and a former SRC with hybrid poplar (Populus maximoviczii × Populus nigra cv. Max) to adjacent arable sites with annual crops or grass. Total fungal and arbsucular mycorrhizal fungal phospholipid fatty acid (PLFA) markers were increased under no-till treatments with permanent crops (SRC and grass) compared to tilled cereals. Enrichments in fungal biomass coincided with C accumulation close to the soil surface (0–5 cm) but was abolished under former SRC after return to annual tillage. This management change altered the spatial distribution but not the accumulation of SOM within the topsoil (0–30 cm). However, lasting qualitative changes in SOM with increased proportions of lignin, lipids and sterols were found under current and former SRC. Increased colonization by arbuscular mycorrhizal fungi was correlated with increased invertase activity (R = 0.64; p < 0.05), carbohydrate consumption and a corresponding accumulation of lignins and lipids in the SOM. This link indicates a regulatory impact of mycorrhizal fungi on soil C dynamics by changing the quality of SOM. Increased stability of SOM to microbial degradation by higher portions of lipids and sterols in the SOM were assumed to be a sustainable effect of poplar growth at Eutric Cambisols.

Variability in DNA Methylation and Generational Plasticity in the Lombardy Poplar, a Single Genotype Worldwide Distributed Since the Eighteenth Century.

In the absence of genetic diversity, plants rely on the capacity of phenotypic plasticity to cope with shifts in environmental conditions. Understanding the mechanisms behind phenotypic plasticity and how local phenotypic adjustments are transferred to clonal offspring, will provide insight into its ecological and evolutionary significance. Epigenetic changes have recently been proposed to play a crucial role in rapid environmental adaptation. While the contribution of epigenetic changes to phenotypic plasticity has been extensively studied in sexual reproducing model organisms, little work has been done on vegetative generations of asexual reproducing plant species. We studied the variability of DNA methylation and bud set phenology of the Lombardy poplar (Populus nigra cv. Italica Duroi), a cultivated tree representing a single genotype worldwide distributed since the eighteenth century. Bud set observations and CpG methyl polymorphisms were studied on vegetative offspring resulting from cuttings grown for one season in a common glasshouse environment. The cuttings were collected from 60 adult Lombardy poplars growing in different environments. The physiological condition of the cuttings was determined by measuring weight and nutrient condition. Methylation sensitive amplified polymorphisms were used to obtain global patterns of DNA methylation. Using logistic regression models, we investigated correlations among epigenotype, bud phenology, and the climate at the home site of the donor trees, while accounting for physiological effects. We found significant epigenetic variation as well as significant variation in bud phenology, in the absence of genetic variation. Remarkably, phenology of bud set observed at the end of the growing season in the common environment was significantly correlated with climate variables at the home site of the mother trees, specifically the average temperature of January and monthly potential evapotranspiration. Although we could not directly detect significant effects of epigenetic variation on phenology, our results suggest that, in the Lombardy poplar, epigenetic marks contribute to the variation of phenotypic response that can be transferred onto asexually reproduced offspring resulting in locally adapted ecotypes. This contributes to the growing evidence that epigenetic-based transgenerational inheritance might be relevant for adaptation and evolution in contrasting or rapidly changing environments.

Características y propiedades físicas de la madera de álamos cultivados en Río Negro, Patagonia Argentina

La populicultura en Norpatagonia, principalmente en la provincia de Río Negro, comenzó con el objetivo de establecer cortinas rompevientos para proteger cultivos frutihortícolas en sus valles irrigados. En la actualidad existen 6000 km de longitud lineal de cortinas y unas 900 ha de plantaciones en macizo de álamo en dicha provincia. El destino de la madera de estos álamos es principalmente la fabricación de embalajes, pero se utiliza también en la construcción, industria del mueble, debobinado y pasta celulósica. No existe información de características y propiedades de esta valiosa materia prima, que es necesaria para optimizar su aprovechamiento y maximizar su valor en diferentes usos. En este trabajo se describen características estéticas, algunas características microscópicas y propiedades físicas de la madera de Populus nigra cv thaisiana, P. alba var bolleana y P. x canadensis ‘conti 12’, a partir de cinco ejemplares adultos de cada especie, provenientes de cortinas rompevientos de la localidad de Allen, provincia de Rio Negro, Patagonia Argentina. La baja densidad (< 0.40) y las características estéticas de la madera de las tres especies determinan su calidad para debobinado, pasta celulósica y fabricación de envases y embalajes. Los valores de contracción volumétrica (11.82%, 10.32% y 12.15%, respectivamente) y del coeficiente de contracción (V: 0.36 - 0.37) indican su ubicación entre las maderas medianamente nerviosas (medianamente estables). Los índices de anisotropía altos (A > 2.3) revelan su baja estabilidad dimensional, indicando la necesidad de realizar correctos secados de la misma para su uso en aberturas y revestimientos.

<i>In Vitro</i> Bioassay of Allelopathy in Four Bamboo Species; <i>Bambusa multiplex, Phyllostachys bambusoides, P. nigra, Sasa kurilensis</i>, Using Sandwich Method and Protoplast Co-Culture Method with Digital Image Analysis

Moderately strong allelopathic activities were found in four bamboo species, Bambusa multiplex cv. Houraichiku; Phyllostachys bambusoides cv. Madake; P. nigra cv. Hachiku; Sasa kurilensis cv. Chishimazasa, which are of different classification or of different ecological distributions, using the “Sandwich Method”, which assays the dried leaves on growth of lettuce seedlings. Only small difference of activity was found among the four bamboo species. In addition, “Protoplast Co-culture Method” for assay of allelopathy in a 50 μL liquid medium using a 96 well culture plate, was applied to the suspension cultures of the four bamboo species. Protoplasts were isolated from two-week cultured suspension cells of four bamboo species using Cellulase RS and Pectolyase Y-23 in 0.6 M mannitol. At low protoplast densities of bamboo, B. multiplex and P. bambusoides stimulated the recipient lettuce growth, i.e., non-spherically cell enlargement and cell divisions observed under an inverted microscope, while protoplasts of P. nigra and S. kurilensis were less stimulatory or inhibitory. Inhibitory effect of S. kurilensis was the strongest among four bamboo species. Furthermore, highly inhibitory effects of S. kurilensis protoplasts on yellow color accumulation of lettuce protoplasts were clearly observed by analysis of a scanned digital image of a 96-well culture plate. Differences and causes of the allelopathic activities were discussed comparing with other plant species studied using the same assay methods.

Phenolic compounds in floral infusions of various Sambucus species and their interspecific hybrids

The main purpose of the present study was to evaluate the diversity and content of various phenolic compounds in floral infusions of 14 elderberry genotypes (3 species and 9 interspecific hybrids). Detailed phenolic analysis was performed using HPLC-MS. Hydroxycinnamic acids (HCAs) were the major phenolic group identified and 3-, 4-, and 5-caffeoylquinic acids were detected in infusions prepared from all analyzed species and interspecific hybrids. Several flavonols were identified in elderberry floral infusions: 8 isorhamnetin derivatives, 6 quercetin derivatives, 2 flavanones, and 6 kaempferol derivatives. The main flavonols detected in all samples were isorhamnetin-3-rutinoside, isorhamnetin dihexoside, quercetin-3-rutinoside, kaempferol-3-rutinoside, and kaempferol dihexoside. The highest levels of flavonols and hydroxycinnamic acids were measured in interspecific hybrid infusions of Sambucus javanica x S. cerulea, (S. javanica x S. nigra) x S. nigra cv. Black Beauty, (S. javanica x S. nigra) x S. nigra, and S. javanica x S. racemosa.

Comparative study of plant growth of two poplar tree species irrigated with treated wastewater, with particular reference to accumulation of heavy metals (Cd, Pb, As, and Ni)

Water is a scarce natural resource around the world which can hamper the socio-economic development of many countries. The Mediterranean area, especially north Africa, is known for its semi-arid to arid climate, causing serious water supply problems. Treated wastewater (TWW) is being used as an alternative strategy for recycling wastewater. It is also a potential source of nutrients for reforestation with certain plant species such as poplar trees, a useful wood resource, and even for phytoremediation purposes. In the present study, we used treated wastewater to irrigate two clones of 1-year-old poplar trees (Populus nigra cv. I-488 and Populus alba cv. MA-104) for 90 days. After a stipulated time, a comparative study was made of the effects of TWW on growth parameters, acquisition of essential minerals (Na, Fe and Zn) and pollutants (Cd, Pb, As and Ni) as well as the enrichment of secondary metabolites such as polyphenolic, flavonoid and tannin compounds which could contribute to the growth and development of poplar plants. The results of this study show that the use of TWW increased P. alba's biomass production by 36% and also enhanced its Cd and Pb accumulation capacity. We also found that P. alba has considerable potential to be used as an alternative plant species for reforestation and/or phytoremediation of toxic metals from contaminated water or effluent.

Modulation in growth, photosynthesis and yield attributes of black mustard (B. nigra cv. IC247) by interactive effect of wastewater and fly ash under different NPK levels

AbstractWaste for fertilization of crop plants has received attention during recent years. The present experiment was conducted for a year on Brassica nigra cv. IC247 using two wastes, i.e. fly ash and wastewater with fertilizers and without fertilizers. The crop was irrigated with ground water and wastewater alone and along with the application of different levels of fly ash (FA0, FA10 and FA20) and different levels of NPK (N0P0K0, N40P15K15, N60P30K30 and N80P45K45). Growth, photosynthesis and yield attributes of the test crop were evaluated at different plant age (A). Result showed that wastewater with fertilizers enhanced growth, photosynthesis and yield parameters as compared to that of ground water with fertilizers. The use of fly ash at 20 t ha−1 performed better than 10 t ha−1. Furthermore, the interactive use of wastewater and fly ash proved to be applicable in making N, P and K optimum at their lower doses, as maximum enhancement in growth, photosynthesis and yield was observed with N60P30K30FA2...

Population Size And Nest Site Selection Of The Spanish Sparrow Passer Hispaniolensis In The Region Of The River Krka (Croatia)

Abstract The breeding range of the Spanish sparrow, Passer hispaniolensis, in Croatia is rapidly expanding. We studied the size of the nesting population and selection of nest site in an area partially included in the Krka National Park. Our results confirm that between 2004 and 2007 in the wider area of the Krka National Park the Spanish sparrow had occupied new localities, and that the number of 160 pairs recorded in 2003 had more than doubled (300–350) by 2007. In the study area, Spanish sparrows nest most commonly in the canopies of introduced planted trees (e.g. Morus alba, Platanus occidentalis, Populus nigra cv. italica). This strategy, with a good access to and diversity of potential nesting sites, enables a further expansion of the species.

Natural hybridization and potential seed set of sympatric Populus nigra and Populus × canadensis along the river IJzer in Flanders (Belgium)

Background In Europe, Populus nigra generally grows sympatric with the exotic related taxon Populus x canadensis. Natural hybridization followed by introgression and genetic swamping is often mentioned as a potential threat for the conservation of P. nigra. However, as evidence for natural hybridization with P. x canadensis is scarce, the significance of this threat is unclear. Methods After first determining the genotypic diversity within 209 trees of P. nigra collected in western Flanders (northwest Belgium), we assessed natural hybridization events between P. nigra females and P. x canadensis males with diagnostic microsatellite markers. We also studied the possible paternity of the frequently planted P. nigra cv. Italica. Furthermore, we compared the potential seed set of P. x canadensis and P. nigra by counting the number of unfertilized ovules per ovary and the number of ovaries per pistillate inflorescences. Results and conclusions Only two different multilocus microsatellite genotypes were detected within the 209 black poplar trees sampled in western Flanders. In 57 % of the seedlings from the open pollinated black poplar trees, at least one species-specific allele of P. deltoides was detected. P. nigra cv. Italica could not be excluded as a father of one seedling. The potential for seed set and the number of ovules per ovary was significantly higher for P. x canadensis compared to P. nigra. Conclusions The extreme low number of P. nigra genotypes in western Flanders suggests a strong human influence on the species’ genetic diversity. The findings further indicate that natural hybridization events between female P. nigra and male P. x canadensis frequently occur in our study area. Furthermore, P. x canadensis has a higher seed set potential compared to P. nigra. Restoration projects of P. nigra in the valley of the IJzer river should initially aim reforestation measures with a mixture of different black poplar genotypes from neighbouring regions.

Seasonal changes in starch and sugar content of poplar (Populus deltoides x nigra cv. Dorskamp) and the impact of stem girdling on carbohydrate allocation to roots

Trees need to store reserves to allow their survival during winter and for bud flush and leaf growth in the following spring. In many tree species, these reserve functions are mainly covered by starch, which is degraded to soluble carbohydrates during the dormant season for maintenance respiration and in spring during bud flush. We conducted girdling experiments on poplar (Populus deltoides x nigra cv. Dorskamp) in order to elucidate how interrupted transport of carbohydrates to the roots during autumn affects plant survival during winter and bud flush in spring. We measured the content of starch, sucrose, glucose, fructose, raffinose and stachyose in stems (above and below the girdle), coarse roots and fine roots over 1 year. We found that, in response to girdling, carbohydrates accumulated in stems above the girdle. As a result of interrupted reserve allocation, girdled plants depleted their root starch reserves nearly to zero, whereas in stems below the girdle, reserves were maintained close to control values, presumably in order to facilitate dormancy release and re-sprouting from buds below the girdle. Furthermore, we showed that stachyose accumulated during winter also in the roots, even in girdled plants, consistent with its importance as freezing protectant. The lower stachyose content of roots compared with shoots was likely due to protection of the roots from cold by the soil.

Paternity analysis ofPopulus nigraL. offspring in a Belgian plantation of native and exotic poplars

Gene flow from cultivated poplar plantations into wild populations of Populus nigra L. is considered to represent a potential threat to the survival of P. nigra. In this study we investigated if pollen competition of Populus nigra L. and Populus × canadensis Moench in fertilising P. nigra ovules detected in a greenhouse experiment also occurs under field conditions. The results confirm non-random mating between males of P. × canadensis and P. nigra in fertilizingP. nigra females in the artificial species-mixed Belgian poplar stand. A paternity analysis also revealed non-random intra-specific mating patterns within P. nigra in the stand. No paternities were assigned to the male cultivar P. nigra cv. Italica. Practical implications for the conservation of wild P. nigra populations are discussed.

Genetical metabolomics of flavonoid biosynthesis in Populus: a case study

Genetical metabolomics [metabolite profiling combined with quantitative trait locus (QTL) analysis] has been proposed as a new tool to identify loci that control metabolite abundances. This concept was evaluated in a case study with the model tree Populus. Using HPLC, the peak abundances were analyzed of 15 closely related flavonoids present in apical tissues of two full-sib poplar families, Populus deltoides cv. S9-2 x P. nigra cv. Ghoy and P. deltoides cv. S9-2 x P. trichocarpa cv. V24, and correlation and QTL analysis were used to detect flux control points in flavonoid biosynthesis. Four robust metabolite quantitative trait loci (mQTL), associated with rate-limiting steps in flavonoid biosynthesis, were mapped. Each mQTL was involved in the flux control to one or two flavonoids. Based on the identities of the affected metabolites and the flavonoid pathway structure, a tentative function was assigned to three of these mQTL, and the corresponding candidate genes were mapped. The data indicate that the combination of metabolite profiling with QTL analysis is a valuable tool to identify control points in a complex metabolic pathway of closely related compounds.

Unusual Fine Root Distributions of Two Deciduous Tree Species in Southern France: What Consequences for Modelling of Tree Root Dynamics?

The spatial distribution of fine roots of two deciduous tree species was investigated in contrasting growing conditions in southern France. Hybrid walnut trees (Juglans regia×nigra cv. NG23) and hybrid poplars (Populus euramericana cv. I214) were both cultivated with or without annual winter intercrops for 10 years on deep alluvial soils. Soil samples for measuring the fine root distribution of both trees and crops were obtained by soil coring down to 3-m depth at several distances and orientations from the tree trunk. The distribution of live fine roots from walnut and poplar trees was patchy and sometimes unexpected. In the tree-only stands, fine root profiles followed the expected pattern, as fine root density decreased with increasing depth and distance from the tree trunk. However, many fine root profiles under intercropped trees were uniform with depth, and some inverse profiles were observed. These distributions may result from a high degree of plasticity of tree root systems to sense and adapt to fluctuating and heterogeneous soil conditions. The distortion of the tree root system was more pronounced for the walnut trees that only partially explored the soil volume: in the tree-only stand, the walnut rooting pattern was very superficial, but in the intercropped stand walnut trees developed a deep and dense fine root network below the crop rooting zone. The larger poplars explored the whole available soil volume, but the intercrop significantly displaced the root density from the topsoil to layers below 1 m depth. Most tree root growth models assume a decreasing fine root density with depth and distance from the tree stem. These models would not predict correctly tree–tree and tree–understorey competition for water and nutrients in 3D heterogeneous soil conditions that prevail under low-density tree stands. To account for the integrated response of tree root systems to such transient gradients in soils, we need a dynamic model that would allow for both genotypic plasticity and transient environmental local soil conditions.

Extensive in vitro cross-reactivity to seed storage proteins is present among walnut (Juglans) cultivars and species.

Tree nuts, including English walnuts (Juglans regia), are sources of food allergens often associated with life-threatening allergic reactions. It is unknown if seed storage proteins from other Juglans species have IgE epitopes similar to those of the important English walnut allergens, Jug r 1 (2S albumin) and Jug r 2 (vicilin-like). To screen for potential germplasm sources of hypoallergenic seed storage proteins of relevance in walnut food allergy. We sought to identify English walnut cultivars (cvs) or other Juglans species that showed decreased IgE binding to major seed storage proteins or an inability to cross-react with Jug r 1 or Jug r 2. We determined if IgE in sera of patients who have had life-threatening systemic reactions to English walnut bound protein extracts from all tested walnut cvs (57 cvs total) or species (six) by Western immunoblot. Further, we used immunoblot inhibition to determine the in vitro cross-reactivity of Jug r 1 and Jug r 2, native and recombinant, with several walnut species. All walnut cvs and species contain allergenic proteins. Furthermore, as shown by in vitro immunoblot inhibition, the major walnut allergens in the species tested cross-reacted with those in J. regia cv. Chandler and J. nigra cv. Thomas extracts. Based on our findings, it is unlikely that a composite hypoallergenic walnut could be bred from available germplasm. In addition, patients with severe allergy to English walnut are likely to be clinically allergic to all commercial English walnut cvs and other closely related Juglans species.

Natural and preservative-treated durability of Populus nigra cv Italica timber grown in Santa Cruz Province, Argentina

Populus nigra cv Italica (Alamo criollo) is the main species planted for windbreaks in Santa Cruz Province (Argentina). Alamo has been a traditional source of poles for rural constructions in southern Patagonia. The objective of this work was to evaluate the natural and CCA-treated durability of P. nigra cv Italica cultivated in different sites of Santa Cruz. Laboratory decay tests were carried out using the modified ASTM Standards D-1413 (1976) and the López and Deschamps (1978) technique, with two fungal species: white rot Trametes versicolor and brown rot Lentinus lepideus . Lenga ( Nothofagus pumilio ) heartwood, a widely used native timber in the region, was also included in the study as a control. Physical and anatomical analyses were carried out. Although important differences were found in anatomical and physical properties of Alamo timbers between sites of, no significant differences were found in relative weight loss over 50 and 150 days, for either fungal species. Natural Alamo timber had the greatest weight loss over 150 days (66.8% for T. versicolor and 29.8% for L. lepideus ). CCA treatment improved the Alamo wood durability compared with Lenga heartwood (1.1% versus 29.2% weight loss with T . versicolor and 2.5% versus 13.6% for L. lepideus , respectively).

Native Venturia inopina sp. nov., specific to Populus trichocarpa and its hybrids

Venturia populina, first described on European Populus nigra, has been thought to be the only species of Venturia in Europe and North America to cause leaf and shoot blight of balsam poplars and cottonwoods in Populus sects. Tacamahaca and Aigeiros. The species of Venturia occurring on introduced P. nigra and native P. trichocarpa in the Pacific northwest were examined. Venturia populina was consistently found on P. nigra (i.e. the widespread P. nigra cv. 'italica') in the region, but V. inopina sp. nov. was present on native P. trichocarpa and its hybrids. There were neither examples of V. populina on P. trichocarpa and its hybrids nor of V. inopina on P. nigra cv. 'italica' (27 collections from 16 sites in Oregon, Washington, and Vancouver Island were made during 1995-2002). In an inoculation study, host-range separation was confirmed in that V. inopina caused sporulating leaf lesions on P. trichocarpa and its hybrids, but only non-sporulating lesions on P. nigra cv. 'italica'. These two species of Venturia can readily be distinguished by conidial septation; V. populina is primarily 2-septate, whereas V. inopina is primarily 1-septate. Growth rates on PDA at 15 degrees C, and ITS sequences (2.3% divergence) were also distinct in isolates of these congeners. Conidial shape was of more value in discriminant analysis than conidial length. Venturia inopina is homothallic, given the sexual fertility of cultures of single ascospores that were overwintered under ambient conditions. Its geographic range appears to be restricted even within the Pacific northwest, leaving open the possibility that still other undescribed, native species of Venturia occur elsewhere in North America on sects. Tacamahaca and Aigeiros.