Can the structure of dormant cambium and the widths of phloem and xylem increments be used as indicators for tree vitality?

We investigated the structure and width of the dormant cambium and of the increments of phloem and xylem of Quercus robur to estimate their potential as indicators for tree vitality. The samples were taken from three woodlands, two in Slovenia [Krakovo forest (KRA) and Murska Suma (MUS)] and one in Croatia [Kobiljak (KOB)], with reported tree decline. The number of dormant cells seems to reflect the initial capacity of the cambium to accomplish cell division. With the exception of two trees at KRA, cell production was always higher on the xylem side than on the phloem side. The annual phloem increments were narrower, less variable among trees and with clear lower and upper limits. With increased cambial cell productivity, the share of the xylem in the total annual radial increment increased following a curvilinear function. In trees with an annual radial increment >3.5 mm, the xylem size represented more than 90 % of the total radial growth. The anatomical variables analyzed show that the most limiting environmental conditions seem to prevail at KRA, whereas the conditions at MUS seem to be most favorable in terms of radial growth. Analysis of the width and structure of xylem and phloem increments, the number of dormant cambial cells and their inter-relationships can provide additional information on the vitality of oaks.     

Anatomische Untersuchungen zur Infektionsbiologie von Sderoderris lagerbergii Gr. [Brunchorstia pinea (Karst.) von Höhn]1

Anatomical studies on the infection biology of Scleroderris lagerberii (Brunchorstia pinea) . Infection of Pinus nigra shoots by B. pinea was studied by means of both ordinary light and fluorescent microscopy. Following spore germination, the mycelium lives under and between the leaf scales, subsequently invading the leaf scales directly. The hyphae can grow through periderms, later invading the xylem via the rays.     

Initial reactions in sapwood of Norway spruce and Scots pine after wounding and infection by Heterobasidion parviporum and H. annosum

The xylem surface of seedlings, stem material and roots of Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) were inoculated with strains of Heterobasidion annosum s. str. and H. parviporum s. str. The depth of necrosis in wounded spruce increased at a linear rate for at least seven weeks of incubation, but the rate of necrotic spread was significantly faster in infected wounds. In wounded pine the necrosis was maintained at a more superficial level for several weeks. Both spruce and pine sapwood were initially infected by hyphae of both species. In spruce, the hyphae advanced at a constant rate behind the necrotic front. On the contrary, after 1–2 weeks living H. parviporum hyphae were rare in pine rays. Heterobasidion annosum hyphae survived in pine rays, phloem and tracheids, despite a heavy accumulation of phenolics and resins and were able to penetrate into the sapwood at a linear rate although slower than infections in spruce. Histochemistry and quantitative estimates demonstrated that peroxidase activity was initially higher in spruce sapwood than in pine. Within three days of incubation, the activity in spruce sapwood disappeared concurrently with deepening necrosis. However, in pine, in both control and infected samples, there was a significant increase in peroxidase activity in the area surrounding the superficial necrosis, up to the wound surface and in the cambium and phloem around the wound. After wounding and infection, the content of soluble protein increased significantly in wood of older trees but not in seedlings. Infection resulted in an increased formation of lipophilic extractives in both spruce and pine but to a significantly greater degree in the latter, whereas the amount of hydrophilic compounds decreased in both. High‐performance liquid chromatography (HPLC) analyses of lipophilic extracts showed that inoculation of pine with the two species of Heterobasidion increased the amounts of pinosylvin, its monomethylether and several other phenolics as also resinous compounds. The results obtained may be relevant in explaining the known higher resistance of Scots pine to H. parviporum.     

Cambial Anatomy and Annual Rhythm of Secondary Xylem Development in the Twigs of Azadirachta indica A. Juss. (Meliaceae) Growing in Different Forests of Gujarat State

Abstract

Seasonal behavior of vascular cambium and development of secondary xylem were studied in the 2-3-years-old branches of Azadirachta indica A. Juss. (Meliaceae) growing in moist deciduous (MDF), dry deciduous (DDF) and scrub land (SF) forests of Gujarat State. Development of xylem began with the sprouting of new leaves in January in both MDF and DDF. Xylem production culminated in July in MDF whereas it reached peak in April and July in DDF. Cambial cells ceased to divide with the maturation of leaves in November and October in MDF and DDF, respectively. Mature xylem and phloem derivatives surrounded the cambium in December in MDF and November in DDF. Radial growth in the branches of trees growing in SF was found continuous throughout the year with peak cambial activity in April, July and November. In all the three forests, maximal radial growth was encountered in July when the rains were heavy. Cambial activity and xylem development showed significant correlation with the phenology of the trees in MDF and DDF whereas cambium was found active throughout the year and no correlation was found between the cambial activity and phenology in SF.     

核桃芽接愈合的组织学机制

【目的】通过对核桃芽接愈合过程的组织学观察,研究不同嫁接时期砧穗在愈伤组织形成、增殖和输导组织连接过程中的组织学变化机制,旨在为核桃和其他木本植物嫁接提供理论指导。【方法】以12年生核桃品种‘香玲’半木质化新梢中部芽片为接穗,2年生本地核桃实生苗为砧木,采用方块芽接法分别于砧木萌芽后40~47天和100~107天2个时间进行芽接试验,采用本课题组建立的非均质化材料切片方法对芽接愈合过程进行组织学观察。【结果】核桃萌芽后40~47天的砧穗愈合方式与前人报道一致,即形成层细胞在嫁接体愈合过程中起主导作用,愈合过程中主要组织学变化包括:隔离层的产生(3天)→砧穗形成层细胞分化产生愈伤组织(4天)→愈伤组织连接(6天)→砧穗原有形成层的修复与连接(12天),完成愈合需要12~15天,成活率达95.6%。而在萌芽后100~107天的砧穗愈合过程中,发现了与上述常规愈合不同的嫁接愈合新方式。此过程中木射线细胞起主导作用,愈合过程依次历经隔离层的产生(3天)→木射线细胞分化产生愈伤组织(4天)→砧穗愈伤组织连接(9天)→导管分化形成(15天)→新的形成层产生以及木射线的连接(25天),需要25~30天才能完成愈合,成活率为61.7%;在木射线细胞主导的砧穗愈合过程中砧木一侧的隔离层要先于接穗发生溶解,在砧穗愈伤组织完成连接时消失,而接穗表面隔离层在愈伤组织分化时依然存在,直至新的形成层产生后才完全溶解消失。【结论】核桃芽接过程中,除了常见的由形成层细胞主导的砧穗愈合方式外,还存在由木射线细胞主导的砧穗木质部的愈合新方式,木射线细胞脱分化产生愈伤组织,并进一步分化出导管、形成层和木射线等组织完成最终的砧穗连接;在此过程中愈伤组织主要来自于砧木木射线细胞且砧木隔离层要先于接穗发生溶解。     

毛白杨形成层的活动周期及其POD同工酶的变化

北京地区生长的毛白杨 (PopulustomentosaCarr .)在春季芽膨大前 ,形成层带已经进入了恢复活动期。在芽展开后一周形成层进入活动期 ,细胞开始分裂 ,细胞层数也有所增加 ,同时分化出未成熟的韧皮部细胞。未成熟韧皮部细胞的数量在形成层活动初期快速增长 ,随后是一个持续而缓慢的连续过程。木质部的产生比韧皮部要晚 3周 ,未成熟的木质部细胞层数在开始变化不大 ,5月底～ 6月底 ,增长速度明显高于初期 ,随后便急剧下降。成熟木质部细胞的出现比成熟的韧皮部细胞要晚约一个月。与其他研究结果不同 ,毛白杨在4月底到 6月底这段时间 ,形成层细胞层数迅速下降 ,未成熟韧皮部细胞也略有减少 ,而未成熟和成熟的木质部细胞则大量增加。木质部在 9月底停止分化 ,较韧皮部要晚约 2 0d。 9月底形成层进入休眠期后 ,形成层细胞层数基本保持不变 ,直到翌年春天恢复活动。毛白杨形成层区域的过氧化物酶 (POD)同工酶在形成层活动期其活性低、酶带少 ,而恢复活动期和休眠期其活性高且酶带多 ,组织化学反应还表明 ,不同时期POD在不同的细胞和组织中的活性不同。本文对POD同工酶在形成层活动周期中的变化与其组织分化的关系进行了讨论。     

Auxin and ethylene regulation of diameter growth in trees

Recent studies on the phytohormonal regulation of seasonal cell-division activity in the cambium, primary-wall radial expansion of cambial derivatives, differentiation of xylem cells, and growth of the cortex in forest trees of the north temperate zone are reviewed. Indol-3-ylacetic acid (IAA, auxin) has been characterized by combined gas chromatography-mass spectrometry (GC-MS) in the cambial region of Abies balsamea, Pinus densiflora, Pinus sylvestris and Quercus robur. All of the evidence supports the hypothesis that developing leaves and extending shoots are primary sources of IAA. The rate of ethylene emanation varies among conifer species when adjoining phloem and cambial tissues are incubated in vitro. The cambium from young cuttings of Abies balsamea produces more ethylene than that from older cuttings. Ethylene production by seven-year-old Abies balsamea cambium is substantially increased in vitro when the tissue is provided with exogenous 1-aminocyclopropane-1-carboxylic acid and IAA. In response to elevated ethylene concentrations, cortex growth is accelerated in both hardwood and conifer seedlings. Ethrel (2-chloroethylphosphonic acid) increases ray size and ray-cell number and promotes traumatic resin-canal development in xylem. In Ulmus americana, endogenous ethylene concentrations are inversely correlated with cambial activity. Ethylene decreases vessel diameter in Acer negundo, Acer platanoides and Ulmus americana. Several studies suggest that ethylene has a role in regulating reaction-wood formation in both conifers and hardwoods.     

Anatomical and cellular responses of Pinus monticola stem tissues to invasion by Cronartium ribicola

White pine blister rust (Cronartium ribicola) causes extensive damage to white pines and their associated ecosystems across North America. The anatomical and cellular characteristics of C. ribicola colonization in Pinus monticola branch and stem tissues were studied as a basis for understanding host tree reactions that may be related to resistance. Samples examined showed typical fusiform swelling and some had produced aecia. The reaction of phloem and xylem tissues was compared with non-infected tissue using light and electron microscopy. Cortical parenchyma and phloem polyphenolic parenchyma cells underwent mitotic division, cell swelling, and ca sixfold greater accumulation of phenolic compounds in colonized vs. control stems. In the cortex and secondary phloem, haustoria were common in parenchymatous cells, and hyphae were abundant in the intercellular spaces, but cell death was rare, unless aecia had ruptured the stem cortex. Hyphae were also common in xylem rays, tracheids and between tracheids. Disease-induced changes in the cambial zone included development of cambium-derived xylem traumatic resin ducts. Results demonstrate that diverse host defence responses were activated in the bark of apparently susceptible trees, but lack of mechanical damage by C. ribicola to the phenol-containing host cells and the resin duct system allowed extensive colonization and development of aecia despite elicitation of these stem defences. Interactions between P. monticola and C. ribicola are discussed and compared with other conifer–fungus pathosystems.     

Infection by Armillaria mellea and some Factors Affecting Host Resistance and the Severity of Disease

Infection by A. mellea in Britain occurs by means of rhizomorphs;the transfer of mycelium at root contacts is probably not importantas a means of spread. Following the initial phase of rhizomorphpenetration, established infection in the cambium is precededby ectotrophic spread of mycelium in the bark scales. Field investigation confirmed reports in the literature thatin susceptible conifers the greatest number of deaths generallyoccurs approximately 6–8 years after planting. However,attacks can also occur in much older crops and the reasons forthis are discussed. Inoculation experiments showed that suppressed trees and thoseexperiencing conditions of reduced light intensity are moresusceptible to infection than dominant trees and trees in fulllight. Species susceptibility in a variety of soils was studiedby inoculation of trees 20–30 cm tall. Of the coniferstested Pseudotsuga menziesii and Abies grandis were more resistantthan Picea abies, P. sitchensis, Larix kaempferi and Pinus sylvestris.Quercus robur and Fagus sylvatica were more resistant than allthe conifers except A. grandis. Soil type influenced diseasedevelopment and the proportion of trees infected was higherin an acidic sand soil than in an alkaline clay soil.     

Responses of water-stressedPinus thunbergii to inoculation with avirulent pine wood nematode (Bursaphelenchus xylophilus): Water relations and xylem histology

The effect of water-stress conditioning on water relations and histological features ofPinus thunbergii Parl. inoculated with avirulent isolate ofBursaphelenchus xylophilus (Steiner and Buhrer) Nickle, pine wood nematode, were investigated. Pines were kept under 8 days cycle of severe water stress. One-half of the water-stressed pines died as a result of infection by avirulent pine wood nematode and water stress tended to induce increased susceptibility and/or decreased resistance of pines to avirulent pine wood nematode. In dead pines, the water conducting function of xylem was lost, and all of the parenchyma cells died. In surviving pines, the xylem hydraulic conductivity and the xylem water content were significantly reduced (12 to 23% and 77 to 83%, respectively) compared to controls. Safranin dye perfusion of excised axis stem segments indicated that the water conductance was limited to the very narrow peripheral area of xylem. Embolism caused by cavitation in the tracheids occurred in the central part of xylem and in that dysfunctional region of the xylem the axial parenchyma cells surrounding the epithelial cells, and ray parenchyma cells partly degenerated but the epithelial cells survived. The disruption of tracheid shape observed in surviving pines indicates that avirulent pine wood nematode temporarily disturbed cell division of the cambium. Considering the differences in responses between dead pines and surviving pines after inoculation with avirulent pine wood nematode, the death of water-stressed pines apparently resulted from death of cells, in particular the vascular cambium and the loss of xylem hydraulic function by cavitation.     

Temporal water deficit and wood formation in Cryptomeria japonica

Cell behavior in the cambium and developing xylem of 3-year-old Japanese cedar (Cryptomeria japonica D. Don.) trees, during and after an 11-day suspension of irrigation, was analyzed. Leaf xylem pressure potential and tangential strain of the stem surface were monitored throughout the experiment. Anatomical features and numbers of developing tracheids and cambial cells were observed in four trees, sampled on Days 0, 4, 8 and 11 after irrigation was suspended. Daytime xylem pressure potential decreased to -1.9 MPa on Day 7 and remained the same until irrigation was resumed on Day 11. The transverse dimensions of the tracheids, which began to form secondary walls, began to decrease on Day 4. The number of cells in the cambial zone and cell expansion zone decreased abruptly on Day 8. Tangentially aligned developing tracheids with collapsed cell walls were observed in samples harvested on Days 8 and 11. Secondary wall formation was recognized in these tracheids. After the resumption of irrigation, xylem pressure potential recovered rapidly to the same value as before the suspension of irrigation. Tangential strain increased within 30 min after the resumption of irrigation, and continued to increase until the onset of light the next day. Eighteen days after the resumption of irrigation, anatomical features of cells in the cambium and cell-expansion zone were similar to those observed before suspension of irrigation.     

CLE多肽激素信号转导在植物维管系统发育分化中的作用

多肽激素参与植物的生长、发育及抗逆等许多生命过程,特别是作为信号分子在细胞与细胞之间的短距离信息交流中起着关键作用。原形成层/形成层细胞通过分裂与分化,在保持自身分生活性的同时,不断生成木质部和韧皮部细胞。近年来研究表明,CLE多肽激素及其类受体激酶通过独特的信号转导机制决定着维管形成层细胞的命运,在调节维管系统的发育方面具有重要的作用。以维管组织为重点,着重介绍CLE多肽激素在控制和影响拟南芥原形成层/形成层细胞分裂和分化方面的信号通路。尽管目前还不清楚CLE多肽激素如何影响木本植物维管形成层的起始、维持及分化,但随着杨树全基因组序列的获得,采用功能基因组学研究策略,将进一步了解林木植物中控制维管形成层细胞分生和分化的重要基因,从而实现调控次生维管系统发育、改良材性的目标。     

华山松大小蠹共生真菌对寄主树木的影响

华山松大小蠹共生真菌（ Ｏｐｈｉｏｓｔｏｍａ ｓｐ ．和Ｌｅｐｔｏｇｒａｐｈｉｕ ｍ ｓｐ ．） 是克服寄主华山松树木抗性系统的先导和致死寄主树木的主要原因。华山松大小蠹共生真菌通过对寄主树木木质部树脂道泌脂细胞的分解和菌丝在寄主树木树脂道内的大量繁殖,堵塞寄主树木树脂道,使寄主华山松泌脂系统失去活性和抗性功能。同时,随共生真菌在寄主树木木质部内的发育,菌丝分解寄主木质部薄壁细胞,使寄主树木木质部物质代谢紊乱,导致寄主华山松迅速死亡     

Are neighboring trees in tune? Wood formation in Pinus pinaster

Neighboring trees growing under identical environmental conditions can exhibit different dynamics and periods of growth. Despite the recent advances in cambial biology, the exogenous and endogenous factors generating asynchronous xylem growths still remain undetermined. This study investigated timings and duration of xylem formation in maritime pine (Pinus pinaster Ait.) from an even-aged plantation in Portugal growing under Mediterranean climate. Cambial phenology and stem diameter were monitored weekly, from March to December 2010, on two classes of trees divided according to the tree ring widths of the last 15 years, but similar age and size: fast- and slow-growing trees. We tested the hypothesis that differences in tree ring widths result from cell production which in turn affects timings of xylogenesis and that the bimodal growth pattern, typical of the Mediterranean, originates from a double reactivation of the cambium: in spring and autumn. Cambial activity started earlier and ended later in fast-growing trees, confirming that cell production is a key factor determining the duration of xylogenesis. Intra-annual variations in stem diameter recorded by band dendrometers revealed two peaks of increment occurring in spring and late summer. However, the number of cambial cells did not increase in late summer, which suggested that the second peak of increment was caused by stem rehydration, rather than by a reactivation of cell division. These results demonstrated that the variability in the timings of xylem phenology observed among trees of the same age and size and growing under similar environmental conditions was closely related to cell production and not to age or size per se.     

Regular cambial activity and xylem and phloem formation in locally heated and cooled stem portions of Norway spruce

The effect of heating (23–25°C) and cooling (9–11°C) on regular cambial activity and xylem and phloem formation in the stem portion of Norway spruce was investigated. Adult trees were sampled at 21-day intervals during the 2005 vegetation period. Continuously elevated temperatures increased the rate of cell division in the first part of the growing season, but did not significantly prolong cambial activity at the end of the vegetation period in the heated tree. Low-temperature treatments shortened regular cambial activity and slowed down cell production. The xylem growth ring was wider in the heated sample and narrower in the cooled sample compared to the control. The temperature in the cambial region was only negligibly transferred along the stem from the site of its application. In general, the temperature in the cambium was affected by a long-term rise or drop in air temperatures. Both experiments affected the structure and width of phloem growth increments. The tangential band of the axial parenchyma was not continuous in the cooled sample. The number of late phloem cells was reduced in the cool-treated sample and increased in the heat-treated sample. Our experiments confirmed the effect of constantly increased or decreased temperatures on regular cambial activity in Norway spruce.     

Disease biology and histopathology of bronze leaf disease: a threat to cultivated aspens,white poplars and their hybrids

Bronze leaf disease (BLD) of species and hybrids of aspens, grey and white poplars (Genus Populus, section Populus) is a systemic disease incited by the fungus Apioplagiostoma populi (E.K. Cash & A.M. Waterman) M.E. Barr that results in a characteristic bronze to dark brown pigmentation of infected leaves in late summer and early fall. Branches on affected trees die over a period of several years, disfiguring trees and eventually leading to mortality of susceptible trees planted in landscapes. In this study, we describe the histopathology of the disease and fungus development relative to external symptoms on affected trees. A. populi hyphae were observed in leaf vessels, lateral veins and xylem vessels of stems and roots of affected trees. Hyphae were also observed in veins and vessels of asymptomatic leaves. Xylem vessels of growth rings on dead branches were completely occluded with A. populi near the vascular cambium and together with the ray parenchyma were stained a bronze colour. Evidence of putative toxin damage to mesophyll cells, not colonized by hyphae, was observed and may contribute to the characteristic tissue staining observed. The development of the fungus was consistent with previous reports, but in this study, we report additional details including perithecial development and ascospore release from predominantly abaxial leaf surfaces. We also report for the first time the isolation and growth of the pathogen in pure culture and systemic infection of roots.     

Hormonal physiology of wood growth in willow (Salix viminalis L.): effects of spermine and abscisic acid

Summary Willow cuttings from two-year-old twigs were grown in nutrient solution alone, nutrient solution with 0.1 mM abscisic acid or with the spermine. Roots and leaves emerged within three weeks and the cambium was activated in the shoot. In most cases earlywood was generated, even when the seedlings were made in late summer. In contrast to plantlets grown in regular nutrient solution, those treated with hormones either inhibited (ABA) or advanced (spermine) the formation of roots, leaves and wood. In addition, SEM observations of wood were combined with autoradiographic studies and metabolite analysis.¹⁴C-labeled photoassimilates from the leaves were unloaded from the phloem of the shoots and transported via the rays into the cambial zone and the xylem. In spermine treated plants labeled assimilates were highly concentrated in all cells of the newly built xylem. However, cells from plants treated with abscisic acid appeared only weakly labeled. Quantitative analysis of the assimilates after two-dimensional thin-layer chromatography showed that wood from spermine-treated plants accumulated 19% more assimilates than the control, while xylem from ABA-treated plants imported 81% less labeled compounds from the phloem. Thus, the results strongly support the view that hormones play a key role in wood formation.     

Xylem dysfunction in Yezo spruce (Picea jezoensis) after inoculation with the blue‐stain fungus Ceratocystis polonica

The blue‐stain fungus Ceratocystis polonica is pathogenic to Norway spruce (Picea abies) in Europe, as well as to Yezo spruce (Picea jezoensis) and Sachalin spruce (Picea glehnii) in Japan. The wilting mechanism in P. jezoensis saplings after inoculation with C. polonica was examined based on anatomical studies of the phloem and xylem of periodically harvested trees. In addition, the course of sap ascent in the trunks was traced by injection of acid fuchsin solution at harvest. As an initial external symptom, needle discolouration was observed. In dye conduction tests, xylem dysfunction in the xylem of inoculated trees became obvious. The dehydrated xylem area (dry zone) had extended more than 20 cm above the inoculation wounds, within 1 month after inoculation. When the sap flow to the branches had nearly stopped, the leaves began to discolour. Hyphae of C. polonica colonized the ray tissue around the inoculation wounds, but were absent at the front of the dry zones. Defence reactions occurred in ray parenchyma cells adjacent to the penetrating hyphae. It is suggested that secondary metabolites, which are formed by the ray cells and epithelial cells of resin canals, are involved in the obstruction of sap flow. Limited necrotic lesions of the phloem and cambium were not associated with foliar symptoms. It is proposed that the dry zone formation caused by C. polonica is the main mechanism leading to tree death.     

Locating the initial in the vascular cambium of Pinus strobus L. by electron microscopy

Summary The results of this investigation by electron microscopy on the vascular cambium in Pinus strobus L. confirm the results of earlier investigations by light microscopy. First, they showed that differences in the thickness of tangential walls of cambial cells exist and that these differences permit grouping of cells according to the sequence of the previous divisions of the initial. This, in turn, permits the site of the initial cell in the cambial zone to be deducted. The thicker distal tangential wall of the initial in the successive series of tissue production allows for precluding the direction in which the initial function proceeds, toward the xylem or toward the phloem. Second, it was demonstrated that immature xylem cells exist in groups of four, that immature phloem cells exist in pairs, and that at all times more cells are produced toward the xylem than toward the phloem. Third, it was shown that the extra-thick tangential wall in immature xylem serves as a landmark to signal the changeover in the initial function from phloem to xylem production.     

Methyl jasmonate and oxalic acid treatment of Norway spruce: anatomically based defense responses and increased resistance against fungal infection

To study the effect of chemical pretreatment on conifer resistance, 13-year-old Norway spruce (Picea abies (L.) Karst.) trees were treated with methyl jasmonate (MJ) or oxalic acid (OxA) on the outer bark and inoculated with the pathogenic blue-stain fungus Ceratocystis polonica (Siem.) C. Moreau 4 weeks later. Both chemicals significantly reduced symptoms of fungal infection, but MJ was more effective than OxA (51 versus 18% reduction in length of necrotic lesions in the phloem relative to untreated control trees). Anatomical examination of treated stem tissues showed that MJ induced extensive formation of traumatic resin ducts in the xylem and extra polyphenolic parenchyma (PP) cells in the secondary phloem between the cambium and the regular annual PP cell layer. No traumatic resin ducts were formed after treatment with OxA, and the coverage of extra PP cells in OxA-treated tissues was not significantly higher than in the controls. The anatomically based defense reactions induced by MJ were similar to the reactions observed after pathogen infection, mechanical wounding and bark beetle attack. Neither MJ nor OxA had apparent phytotoxic effects on Norway spruce at the concentrations used, with needle and stem tissues of all trees appearing normal without visible symptoms of toxicity. However, trees treated with MJ had 30% less radial sapwood growth than control trees. In conclusion, MJ treatment of Norway spruce appears to have practical potential as a tool for increasing plant resistance to fungal infection, but with a modest reduction in sapwood growth.