Trunk Wood Research Articles

First Report of Citrus Blight in Costa Rica.

Citrus blight (CB), causing a chronic decline of citrus, has been an important disease in Florida for over 100 years. CB was first reported in Brazil in the 1980s and is now responsible for the removal of nearly 10% of the trees from production annually. No causal agent has been identified, but CB has been root-graft transmitted to healthy trees, suggesting that the causal agent is infectious (3). Since 1997, CB symptoms were observed in several groves in northern Costa Rica, the most important citrus area of approximately 25,000 ha. Symptoms observed include a general decline and wilt of the tree canopy, off-color leaves, leaf drop, twig dieback, small fruit, delayed blossom, poor growth, and death. A survey near Guanacaste revealed CB symptoms in 7-yr-old Valencia and Pineapple orange trees (Citrus sinensis (L.) Osbeck) grafted on Carrizo citrange (C. sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf.) rootstock. Since 1997, 6% of the trees in this area have been replanted annually because of CB symptoms. Similar situations were observed in other groves in the northern citrus area. Dot immunobinding assays (DIBA) (1) were used to detect the P12 protein associated with CB with 20 of 22 trees showing CB-like symptoms giving a positive test. Zinc (Zn) accumulation in trunk wood and water uptake tests were done according to Roistacher (2) in 8 healthy and 20 symptomatic trees which were positive for CB using DIBA. The average Zn concentration of 16 declining trees was 4.6 ± 1.9, whereas the average concentration for 8 healthy trees was 2.0 ± 0.9. The average water uptake in 1 min was 14 ml for healthy trees, and virtually zero for the 20 symptomatic trees. These diagnostic tests confirm the presence of CB in the northern citrus area of Costa Rica, and the surveys indicate the disease is beginning to spread and become economically important. To our knowledge, this is the first report of CB in commercial citrus in Costa Rica.

Identification of Eutypa lata by PCR-RFLP.

Eutypa lata is a vascular canker pathogen of woody plants commonly diagnosed by isolating the pathogen from infected tissue. Related fungi from the same family, the Diatrypaceae, also have been found in association with grapevine in Californian vineyards. An in situ polymerase chain reaction (PCR) method has been developed for detection of E. lata in infected wood tissue. However, our results indicate that this method also would amplify other Diatrypaceous fungi, which could potentially lead to an incorrect diagnosis. Therefore, we developed a PCR-restriction fragment length polymorphism (PCR-RFLP) assay. The internal transcribed spacer (ITS)1/5.8S/ITS2 ribosomal DNA region was amplified by PCR using universal primers, and RFLP patterns were determined after digestion with AluI. The restriction profiles obtained served to distinguish E. lata from wood trunk pathogens of grapevine (Phomopsis viticola, Botryodiplodia sp., Phaeoacremonium aleophilum, and Phaeomoniella chlamydospora), Diatrypaceous fungi (Diatrype sp., Diatrypella sp., Eutypella vitis, and Eutypa leptoplaca), and Cryptovalsa sp. found on dead wood of grapevine, and other Eutypa spp. (E.petrakii var. hederae, E. astroidea, E. crustata, and E. lejoplaca), with the exception of E. armeniacae, which we regard as a synonym for E. lata, and E. laevata, which has not been found on grapevine.

Dutch forest monitoring network, design and results

The new Dutch forest monitoring network is a policy-guided, multiple-use, GIS-oriented forest monitoring network. It is designed to provide the Dutch government, on a cyclic 8-year basis, with actual information about Dutch forests. Variables that reflect the information needs of policy makers and interest groups were selected by means of interviews and workshops. High-ranking variables are: wood stock, ownership, stand age, management status, biodiversity, carbon stock, and recreational use. These and other variables are being measured in 3622 forest sites, selected according to an unaligned systematic sampling design. The data are stored in an ORACLE data base, made accessible through the internet. The Dutch forest area approximates a total of 360 000 ha; 46% is owned by private owners and organisations for nature conservation. Coniferous forests dominate (60%). Most forests were planted in 1940-1980. The total above ground volume of living trunk wood amounts to 56.3 million m3. The most common tree sp...

Processes, dynamics and modelling of radiocaesium cycling in a chronosequence of Chernobyl-contaminated Scots pine ( Pinus sylvestris L.) plantations

In a large forested area affected by the Chernobyl radioactive fallout, especially in CIS, the lasting recycling of radiocaesium ( 137Cs) by the trees is a source of long-term contamination of woody products. The quantitative description of the 137Cs dynamics in contaminated forest is a prerequisite to predictive modelling and further management of such territories. Three even-aged mono-specific Scots pine stands (17, 37 and 57 years old) were selected in a contaminated woodland in southeastern Belarus to constitute an adequate chronosequence. We determined the potassium and radiocaesium annual fluxes involved in the biological cycling in each stand using a well-documented calculation methodology. Qualitatively, 137Cs was shown to be rapidly recycled in trees through the same pathways as K and to redistribute similarly between the tree components. Compared to K, a higher fraction of 137Cs, corresponding to about the half of the annual uptake, is immobilised in perennial organs. With tree development, trunk wood and bark become prevailing sinks for 137Cs since they represent an increasing pool of biomass. In the pine chronosequence, the current root absorption, respectively, mobilizes 0.53, 0.32 and 0.31% year −1 of the total 137Cs pool in soil. Variations in the 137Cs uptake do not reflect differences in the 137Cs balance between stands. In the two older stands, 51 and 71% of the current tree contamination are related to earlier accumulation subsequent to the initial fallout interception and recycling. The soil is the dominant source of long-term tree contamination. A simple modelling based on the measured 137Cs fluxes indicates that, for young stands, radioactive decay-corrected contamination would stabilize after reaching a maximum of 25 years after the 137Cs deposition. Stemwood presents a maximum of 15 years after the deposition and decrease afterwards mainly through radioactive decay. In the older stands, the decontamination is constant without local maximum of 137Cs level in the wood. The 137Cs contamination of tree components is the result of different influential processes like root uptake, internal translocation and immobilisation. For more accurate predictions, the calibration of existing models would be benefited by comparing with the 137Cs annual fluxes instead of the simple transfer factor coefficients. In the perspective of other applications, there is a need of such data for other radionuclides as well as for heavy metals.

Projecting Diameter Growth in Tropical Trees: A New Modeling Approach

Abstract An important and heretofore unresolved challenge in forestry has been how to project long-term tree growth (i.e., decades to hundreds of years) from short-term measurements (here 1 year) for trees that do not present annual growth rings in their trunk wood. Such a method is crucial in the lowland tropics, where few long-term growth measurements have been taken, and where frequently trees lack reliable annual growth rings because of the lack of winters or highly seasonal dry periods. The new piecewise linear (PL) growth model, developed in this article, relates logarithmic relative growth to trunk diameter. Having obtained the coefficients from piecewise linear regression, the long-term age-diameter curve is calculated, i.e., the expected average growth curve of a statistical population of individual trees. The model is applied to the following five tree species without annual growth rings from the tropical rainforest in Los Tuxtlas (Veracruz, Mexico): Aspidosperma megalocarpon, Cordia alliodora, Dialium guianense, Guarea grandifolia, and Persea schiedeana. Using the tools of multiple linear regression, the PL model is highly flexible to derive sigmoid, exponential, and over-exponential growth separately for different diameter segments. FOR. SCI. 50(2):213–224.

Seasonal changes in gene expression at the sapwood-heartwood transition zone of black locust (Robinia pseudoacacia) revealed by cDNA microarray analysis.

Heartwood is a determining factor of wood quality and understanding the biology of heartwood may allow us to control its formation. Heartwood formation is a form of senescence that is accompanied by a variety of metabolic alterations in ray parenchyma cells at the sapwood-heartwood transition zone. Although senescence has been studied at the molecular level with respect to primary growth, the cell maturation and death events occurring during heartwood formation have been difficult to study because of their location and timing. Analysis of global gene expression patterns during the transition from sapwood to heartwood may offer a powerful means of identifying the mechanisms controlling heartwood formation. Previously, we developed cDNA microarrays carrying 2567 unigenes derived from the bark/cambium region, sapwood and transition zone of a mature black locust tree. Here, we describe the use of these microarrays to characterize seasonal changes in the expression patterns of 1873 genes from the transition zone of mature black locust trees. When samples collected in summer and fall were compared, 569 genes showed differential expression patterns: 293 genes were up-regulated (> twofold) in summer (July 5) and 276 genes were up-regulated in fall (November 27). More than 50% of the secondary and hormone metabolism-related genes on the microarrays were up-regulated in summer. Twenty-nine out of 55 genes involved in signal transduction were differentially regulated, suggesting that the ray parenchyma cells located in the innermost part of the trunk wood react to seasonal changes. We established the expression patterns of 349 novel genes (previously unknown or no-hit), of which 154 were up-regulated in summer and 195 were up-regulated in the fall.

Functional characterization of allantoinase genes from Arabidopsis and a nonureide-type legume black locust.

The availability of nitrogen is a limiting factor for plant growth in most soils. Allantoin and its degradation derivatives are a group of soil heterocyclic nitrogen compounds that play an essential role in the assimilation, metabolism, transport, and storage of nitrogen in plants. Allantoinase is a key enzyme for biogenesis and degradation of these ureide compounds. Here, we describe the isolation of two functional allantoinase genes, AtALN (Arabidopsis allantoinase) and RpALN (Robinia pseudoacacia allantoinase), from Arabidopsis and black locust (Robinia pseudoacacia). The proteins encoded by those genes were predicted to have a signal peptide for the secretory pathway, which is consistent with earlier biochemical work that localized allantoinase activity to microbodies and endoplasmic reticulum (Hanks et al., 1981). Their functions were confirmed by genetic complementation of a yeast mutant (dal1) deficient in allantoin hydrolysis. The absence of nitrogen in the medium increased the expression of the genes. In Arabidopsis, the addition of allantoin to the medium as a sole source of nitrogen resulted in the up-regulation of the AtALN gene. The black locust gene (RpALN) was differentially regulated in cotyledons, axis, and hypocotyls during seed germination and seedling growth, but was not expressed in root tissues. In the trunk wood of a mature black locust tree, the RpALN gene was highly expressed in the bark/cambial region, but had no detectable expression in the sapwood or sapwood-heartwood transition zone. In addition, the gene expression in the bark/cambial region was up-regulated in spring and fall when compared with summer, suggesting its involvement in nitrogen mobilization.

Mineral deficiency and the presence of Pinus sylvestris on mires during the mid- to late Holocene: palaeoecological data from Cadogan's Bog, Mizen Peninsula, Co. Cork, southwest Ireland

Pollen records across parts of Ireland, England and northern Scotland show a dramatic collapse in Pinus pollen percentages at approximately 4000 radiocarbon years BP. This phenomenon has attracted much palaeoecological interest and several hypotheses have been put forward to account for this often synchronous and rapid reduction in pine from mid-Holocene woodland. Explanations for the ‘pine decline’ include prehistoric human activity, climatic change, in particular a substantial increase in precipitation resulting in increased mire wetness, and airborne pollution associated with the deposition of tephra. Hitherto, one largely untested hypothesis is that mineral deficiency could adversely affect pine growth and regeneration on mire surfaces. The discovery of pine-tree remains (wood pieces, stumps and trunks) within a peat located at Cadogan's Bog on the Mizen Peninsula, southwest Ireland, provided an opportunity to investigate the history of Pinus sylvestris and also to assess the importance of mineral nutrition in maintaining pine growth on mires. Pollen, plant macrofossils, microscopic charcoal and geochemical data are presented from a radiocarbon dated monolith extracted from this peat together with tree ring-width data and radiocarbon dated age estimates from subfossil wood. Analyses of these data suggest that peat accumulation commenced at the site around 6000 years BP when pine was the dominant local tree. Thereafter Pinus pollen percentages diminish in two stages, with the second decline taking place around 4160 6 50 years BP. Concomitant with this decline in Pinus pollen, there is a noticeable, short-lived increase in wet-loving mire taxa and a decrease in the concentration of phosphorus, potassium, magnesium, calcium, sodium, iron and zinc. These results suggest that increased mire surface wetness, possibly the result of a change in climate, created conditions unsuitable for pine growth c. 4000 years BP. Mire surface wetness, coupled with a period of associated nutrient deficiency, appears to be a possible explanation for a lack of subsequent pine-seedling establishment for most of the later Holocene.

Wood-fuel yields in short-rotation coppice growth in the north Sudan savanna in Burkina Faso

Woody growth at five sites, covering a range of precipitation (620–785 mm) and soil conditions in North Sudan zone in Burkina Faso was investigated 5–14 years after clear-cutting. Woody growth ranged from 0.7 to 1.7 Mg ha −1 per year, corresponding to 1.0–2.4 m 3 ha −1 per year in terms of green volume when species-specific basic densities were applied. Trunks (girth more than 10 cm), branches and stemlets made up about a third each of the yield and about one-third of the trunk was bark. Thus, the actual trunk wood production ranged from 0.2 to 0.7 Mg ha −1 per year corresponding to 0.3–0.9 m 3 ha −1 per year. Woodfuel yield was reduced to about a fourth of the total yield, when excluding small dimensions and trunk-bark, species with low calorific value or multiple use, e.g. fruit bearing or forage. Each site was dominated by some few species in terms of percentage of dry mass: Sclerocarya birrea (13%), Anogeissus leiocarpus (57%), Acacia seyal (38%), Combretum glutinosum (17%) and Combretum nigricans (37%). Mean stool growth per site ranged from 0.5 to 1.7 kg per year. Largest stool growth was recorded for S. birrea and A. leiocarpus with 4.1 and 3.6 kg per stool per year, respectively.

Gastroprotective and anti-inflammatory effects of resin from Protium heptaphyllum in mice and rats

The natural resin collected from the trunk wood of Protium heptaphyllum is used in folk medicine to treat inflammatory conditions and to hasten wound repair. In the search of new potential anti-inflammatory agents with gastroprotective property, the present study evaluated its effects in experimental models of gastric ulcer and inflammation. In mice, the resin (200 and 400 mg/kg) significantly attenuated the gastric damage induced by ethanol or acidified ethanol (HCl/ethanol), in a manner similar to N-acetyl- l-cysteine (NAC), a replenisher of sulfhydryls. Unlike NAC the resin failed to restore the ethanol-induced depletion of non-protein sulfhydryl content, indicating a different mechanism of gastroprotection. However, in 4-h pylorus-ligated rats, the resin significantly reduced the total acidity without much change in gastric secretory volume. In rats, at similar doses the resin did not modify the hind-paw edema induced by carrageenan, but effectively reduced the formation of cotton pellet-induced granuloma, suggesting its inhibitory effect on collagen formation but not on acute edema. Furthermore, the vascular permeability increase induced by acetic acid was significantly reduced in mice that received 400 mg/kg resin. The resin demonstrated no overt toxicity in mice up to an oral dose of 5 g/kg. Phytochemical analysis revealed the presence of α- and β-amyrins as principal triterpenoid constituents of resin, which were previously described to have anti-ulcer property. These findings indicate the potential gastroprotective and anti-inflammatory property of P. heptaphyllum resin and further support its popular use in gastrointestinal disorders.

Tracheid diameter is the key trait determining the extent of freezing-induced embolism in conifers.

We tested the hypotheses that freezing-induced embolism is related to conduit diameter, and that conifers and angiosperms with conduits of equivalent diameter will exhibit similar losses of hydraulic conductivity in response to freezing. We surveyed the freeze-thaw response of conifers with a broad range of tracheid diameters by subjecting wood segments (root, stem and trunk wood) to a freeze-thaw cycle at -0.5 MPa in a centrifuge. Embolism increased as mean tracheid diameter exceeded 30 microm. Tracheids with a critical diameter greater than 43 microm were calculated to embolize in response to freezing and thawing at a xylem pressure of -0.5 MPa. To confirm that freezing-induced embolism is a function of conduit air content, we air-saturated stems of Abies lasiocarpa (Hook.) Nutt. (mean conduit diameter 13.7 +/- 0.7 microm) by pressurizing them 1 to 60 times above atmospheric pressure, prior to freezing and thawing. The air saturation method simulated the effect of increased tracheid size because the degree of super-saturation is proportional to a tracheid volume holding an equivalent amount of dissolved air at ambient pressure. Embolism increased when the dissolved air content was equivalent to a mean tracheid diameter of 30 microm at ambient air pressure. Our centrifuge and air-saturation data show that conifers are as vulnerable to freeze-thaw embolism as angiosperms with equal conduit diameter. We suggest that the hydraulic conductivity of conifer wood is maximized by increasing tracheid diameters in locations where freezing is rare. Conversely, the narrowing of tracheid diameters protects against freezing-induced embolism in cold climates.

Trace Metal Concentrations in Ashes from Various Types of Biomass Species

In this study, toxic metal levels in selected samples of various biomass types—wood, wood bark, fruit shell, mushroom, and lichen—were determined. The samples were analyzed by atomic absorption spectrophotometrically for their toxic metal elements: As, Cd, Cr, Cu, Pb, and Hg. The maximum levels of As, Cd, Cr, Cu, Pb, and Hg were 4.118 mg/kg in beech trunk wood ash, 3.926 mg/kg in Cladonia rangiformis, 15.057 mg/kg in Lactarius piperatus, 92.488 mg/kg in Amanita muscaria, 40.832 mg/kg in beech trunk bark ash, and 0.718 mg/kg in Cladonia rangiformis, respectively, in all the samples. The problem of uptake and accumulation of these elements has environmental and toxicological aspects as well. Air toxic emissions during biomass combustion were typically very low and often near or below detection limits.

Novel gene expression profiles define the metabolic and physiological processes characteristic of wood and its extractive formation in a hardwood tree species, Robinia pseudoacacia.

Wood is of critical importance to humans as a primary feedstock for biofuel, fiber, solid wood products, and various natural compounds including pharmaceuticals. The trunk wood of most tree species has two distinctly different regions: sapwood and heartwood. In addition to the major constituents, wood contains extraneous chemicals that can be removed by extraction with various solvents. The composition and the content of the extractives vary depending on such factors as, species, growth conditions, and time of year when the tree is cut. Despite the great commercial and keen scientific interest, little is known about the tree-specific biology of the formation of heartwood and its extractives. In order to gain insight on the molecular regulations of heartwood and its extractive formation, we carried out global examination of gene expression profiles across the trunk wood of black locust (Robinia pseudoacacia L.) trees. Of the 2,915 expressed sequenced tags (ESTs) that were generated and analyzed in the current study, 55.3% showed no match to known sequences. Cluster analysis of the ESTs identified a total of 2278 unigene sets, which were used to construct cDNA microarrays. Microarray hybridization analyses were then performed to survey the changes in gene expression profiles of trunk wood. The gene expression profiles of wood formation differ according to the region of trunk wood sampled, with highly expressed genes defining the metabolic and physiological processes characteristic of each region. For example, the gene encoding sugar transport had the highest expression in the sapwood, while the structural genes for flavonoid biosynthesis were up-regulated in the sapwood-heartwood transition zone. This analysis also established the expression patterns of 341 previously unknown genes.

Essential Oil of Aniba puchury-minor (Mart.) Mez Occurring in the Amazon

The leaf, wood bark and trunk wood oils of Aniba puchury-minor were hydrodistilled and analysed by GC-MS. The main compounds identified in the leaf oil were elemicin (21.5%), Bicycologermacrene (15.4%), Spathulenol (11.3%), (E)-isoelemicin (8.3%), α-copaene (6.6%), myristicin (6.4%), and β-selinene (6.3%). The wood bark oil was dominated by (E)-methyl isoeugenol (43.1%), (E)-asarone (30.0%), (Z)-methyl isoeugenol (9.0%), and (E)-isoelemicin (5.0%). The major constituents found in the trunk wood oil were (E)-asarone (38.2%), (E)-isoelemicin (23.1%), (Z)- methyl isoeugenol (14.8%) and (Z)-isoelemicin (10.1%).

Seasonal essential oil variation of Aniba canelilla

The essential oils of leaves, stem bark and trunk wood of Aniba canelilla, collected in the rainy and dry season from different soil types, were obtained by hydrodistillation and analysed by GC/MS. It has been observed that methyleugenol is also an important volatile constituent in the essential oil of A. canelilla, as well as 1-nitro-2-phenylethane. The percentage content of these two compounds was depending on the season time. In the rainy period the 1-nitro-2-phenylethane reach values near 95%, while methyleugenol remain below 18%. By contrast, in the dry period 1-nitro-2-phenylethane decrease to 39%, while methyleugenol reach 45%. The leaf oils produced from specimens collected at different soil types in the dry season presented the lower percentage contents to 1-nitro-2-phenylethane and methyleugenol. In contrast, the mono- and sesquiterpenes compounds present in the same oils showed the higher percentage contents.

Essential Oil from Aniba riparia (Nees) Mez

The essential oils of some parts of Aniba riparia were obtained by hydrodistillation and analyzed by GC/MS. The majorcomponents identified in the leaf oil were β-caryophyllene (16.9%), α-humulene (14.9%) and bicyclogermacrene (14.1%). The main volatile compound found in the bark wood and trunk wood oils was benzyl benzoate (30.9% and 36.2%, respectively). The thin branch oil was dominated by (E)-nerolidol (19.4%), elemol (16.2%) and α-humulene (10.9%).

Growth strain in coconut palm trees.

Until recently, growth stress studies have been made only on coniferous and dicotyledonous trees. Growth stress of trees is thought to be initiated in newly formed secondary xylem cells. This stress can accumulate for years and is distributed inside the trunk. Major characteristics of the trunk of monocotyledonous trees include numerous vascular bundles scattered inside the ground tissue and the lack of secondary growth for enlarging the diameter of the trunk. We used the strain gauge method to measure the released growth strain of the monocotyledonous woody palm, coconut (Cocos nucifera L.), and to investigate the surface growth strain of the trunk and central cylinder at different trunk heights. The internal strains of both vertical and leaning trunks were measured and compared with those of coniferous and dicotyledonous trees. We found that tensile stress existed longitudinally on the surface of vertically growing trunks, whereas compression stress was found at the bending position of leaning trunks. Compression stress was found in the outer part of the central cylinder, whereas tensile stress is generally found in the outer part of the trunk in coniferous and dicotyledonous trees. The distribution of strain in the palm trunk is similar to that of compression wood of the leaning trunk of a conifer. Specific gravity was greater in the outer part of the trunk than in the inner part of the trunk. This difference may be related to the distribution of growth stress.

Seasonal changes of sucrose-phosphate synthase and sucrose synthase activities in poplar wood ( Populus × canadensis Moench ‘ robusta ’) and their possible role in carbohydrate metabolism

Summary Two important enzymes of sucrose metabolism, sucrose-phosphate synthase (SPS, EC 2.4.1.14) and sucrose synthase (SuSy, EC 2.4.1.13), were investigated in the ray parenchyma cells of the trunk wood of Populus × canadensis Moench ‘robusta’ throughout the year. The activity of SPS increases dramatically in autumn in parallel with leaf fall, reaches a maximum level in winter at the time of the starch-to-sugar conversion and declines in spring during starch resynthesis and mobilisation. In summer, the activity of SPS remains at a very low level. These seasonal changes in SPS activity were identical both under Vmax- and under Vlim-assay conditions. In temperature-controlled storage experiments with twig sections, the activation state of SPS, termed as Vlim/Vmax × 100, was substantially higher after storage at -5 °C in contrast to storage at +10 °C. A Western blot analysis, using a polyclonal antibody, revealed a molecular weight of about 130 kD for the SPS-polypeptide in poplar wood with highest levels of SPS enzyme protein in winter and lowest levels in summer. SPS of other tree species (Acer, Fagus, Salix) exhibited a molecular weight in a similar range. The activity of SuSy started to increase in late autumn, was high in winter and declined in spring. In contrast to SPS, SuSy shows a remarkably high activity in the outer wood area in summer while it remained low in the middle and inner area of the trunk wood. This high SuSy activity correlates with the differentiation of the xylem cells rather than with starch deposition. The significance of the SPS in autumn and winter for the starch-to-sugar conversion during cold adaptation of xylem parenchyma cells and of the SuSy for wood formation processes is discussed.

Occurrence of Fusarium‐produced naphthazarins in citrus trees and sensitivity of rootstocks to isomarticin in relation to citrus blight

Fusarium solani, the causal fungus of root and crown rot of citrus, produces naphthazarin toxins that were shown to be toxic to citrus plants. It was found that citrus trees in South Africa had varying levels of naphthazarins in their xylem. Significantly higher concentrations of these toxins were detected in trees with blight symptoms than in symptomless trees. Citrus seedlings grown in hydroponic culture containing isomarticin showed inhibition of growth, shortening of roots and accumulation of zinc in the trunk wood. Zinc deficiency symptoms were also observed on certain rootstocks. A procedural ranking of rootstocks indicated that trees with observed tolerance to blight in the field generally had higher tolerance to isomarticin in hydroponic culture, whereas trees susceptible to blight were more sensitive to the toxin. These findings indicate that Fusarium‐produced isomarticin is involved in the induction of some of the symptoms associated with citrus blight syndrome.

Dynamic behaviour of 137Cs contamination in trees of the Briansk region, Russia

Seven trees were felled in the Briansk region in 1997. The trees were sectioned for sampling, both at different heights and according to year rings, and samples were analysed for content of 137Cs. In general, the specific activity of 137Cs was much higher in the fresh parts of the three (needles, leaves and twigs) than in the core wood. The year ring study showed that 137Cs had penetrated deeply in to the trunk, and no peak was detectable in the year ring corresponding to the Chernobyl accident in 1986. The specific activity in the trunk wood had a maximum at the height corresponding to the growth years at approximately 1986. Neutron activation analysis was used to analyse for stable Cs. The results showed that the relationship between concentrations of 137Cs and stable caesium is much higher in the newer parts of growing trees than in the older parts. Together with a tendency of inward migration this leads to a preliminary conclusion that the 137Cs activity will continue to accumulate in the core wood.