Nina Elisabeth Nagy

Research Professor

(+47) 994 91 503
nina.elisabeth.nagy@nibio.no

Place
Ås H8

Visiting address
Høgskoleveien 8, 1433 Ås

Abstract

Dieback of European ash, caused by the ascomycete Hymenoscyphus fraxineus originating from Asia, has rapidly spread across Europe, and is threatening this keystone tree at a continental scale. High propagule pressure is characteristic to invasive species. Consistently, the enormous production of windborne ascospores by H. fraxineus in an ash forest with epidemic level of disease obviously facilitates its invasiveness and long distance spread. To understand the rate of build-up of propagule pressure by this pathogen following its local introduction, during 2011–2017 we monitored its sporulation at a newly infested ash stand in south-western Norway characterized with mild winters and cool summers. We also monitored the propagule pressure by Hymenoscyphus albidus, a non-pathogenic native species that competes for the same sporulation niche with H. fraxineus. During the monitoring period, crown condition of ash trees had impaired, and 20% of the dominant trees were severely damaged in 2017. H. fraxineus showed an exponential increase in spore production between 2012 and 2015, followed by drastic decline in 2016 and 2017. During 2011–2013, the two Hymenoscyphus species showed similar sporulation level, but thereafter spores of H. albidus were no longer detected. The data suggest that following local introduction, the population of H. fraxineus reaches rapidly an exponential growth stage if the local weather conditions are favorable for ascomata maturation across years. In the North Atlantic climate, summer temperatures critically influence the pathogen infection pressure, warm summers allowing the population to grow according to its biotic potential, whereas cold summers can cause a drastic decline in propagule pressure.

Abstract

In Norway the common ash (Fraxinus excelsior L.) has its northernmost distribution in Europe. It grows along the coastal range as small fragmented populations. The first occurrence of ash dieback caused by Hymenoscyphus fraxineus in Norway was reported in 2008. At that time, the disease had already spread through large areas of southern and south-eastern parts of Norway. Since then the disease continued spreading with a speed of about 50- 60 km per year along the western coastal range. To monitor the disease development over time, we established eight permanent monitoring plots in south-eastern and western Norway in 2009 and 2012, respectively. In all plots tree mortality was high, especially among the youngest trees in south-eastern Norway. The extent of crown damage has continually increased in all diameter classes for both regions. In 2009, 76.8 % of all trees on the five monitoring plots in south-eastern Norway were considered to be healthy or slightly damaged, and only 8.9 % to be severely damaged. In 2015, 51.7 % were dead, 13.5 % severely damaged and only 25.7 % remained healthy or slightly damaged. To assess the infection pressure and spore dispersal patterns of the pathogen, we used a Burkard volumetric spore sampler placed in an infested ash stand in southern Norway. We examined the airborne ascospores of H. fraxineus and H. albidus captured on the sampling tape microscopically and with real-time PCR assays specific to these fungi. We detected very few ascospores of H. albidus, whereas ascospores of H. fraxineus dominated throughout entire sampling periods of 2009, 2010 and 2011. Spore discharge occurred mainly between the hours of 5 and 8 a.m., though the distinctive sporulation had yearly variation between 5-7 a.m. We observed the same diurnal pattern throughout the entire sampling period, with a seasonal peak in spore liberation between mid-July and midAugust, after which the number of ascospores decreased substantially. Similar diurnal patterns were observed throughout the sampling period except that after mid-August the number of trapped ascospores substantially decreased. To compare the genetic pattern of common ash in the northern and central ranges of Europe we analyzed the Norwegian samples together with available samples from central Europe by using chloroplast and nuclear microsatellite markers. We found that the northern range of common ash was colonized via a single migration route that originated in eastern or south-eastern Europe with little influence originating from other southern or western European refugia. In the northern range margins, genetic diversity decreased and population differentiation increased, coherent with a post-glacial colonization history characterized by founder events and population fluctuations. Based on our findings we discuss the future management and conservational implications.

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Abstract

Dieback of European ash (Fraxinus excelsior L.), a disease caused by the ascomycete Hymenoscyphus fraxineus (previously referred to as H. pseudoalbidus or Chalara fraxinea), was first observed in Poland in the early 1990ies, and is currently present almost throughout the entire distribution area of European ash. The characteristic symptoms of the disease include dead shoots with necrotic lesions in the bark and discoloration of xylem and pith but the seasonal dynamics of pathogen spread in shoot tissues remain poorly understood. To investigate whether the internal spread of the fungus involves season-specific patterns, saplings with necrotic bark lesions in 1-2 -year-old stem regions were collected during 2014-2015 at time intervals in spring, summer, autumn and winter at several localities in western Ukraine and at two localities in south-eastern Norway. Tissuespecific presence of H. fraxineus was determined by a highly sensitive quantitative real-time PCR assay that is specific to DNA of H. fraxineus. The relatively high proportion of bark samples positive for H. fraxineus in the saplings collected during spring provides support to a model that H. fraxineus can be a primary causative agent of bark lesions and that other fungi may eventually replace it in old infection areas.

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Abstract

High biodiversity is regarded as a barrier against biological invasions. We hypothesized that the invasion success of the pathogenic ascomycete Hymenoscyphus fraxineus threatening common ash in Europe relates to differences in dispersal and colonization success between the invader and the diverse native competitors. Ash leaf mycobiome was monitored by high-throughput sequencing of the fungal internal transcribed spacer region (ITS) and quantitative PCR profiling of H. fraxineus DNA. Initiation of ascospore production by H. fraxineus after overwintering was followed by pathogen accumulation in asymptomatic leaves. The induction of necrotic leaf lesions coincided with escalation of H. fraxineus DNA levels and changes in proportion of biotrophs, followed by an increase of ubiquitous endophytes with pathogenic potential. H. fraxineus uses high propagule pressure to establish in leaves as quiescent thalli that switch to pathogenic mode once these thalli reach a certain threshold – the massive feedback from the saprophytic phase enables this fungus to challenge host defenses and the resident competitors in mid-season when their density in host tissues is still low. Despite the general correspondence between the ITS-1 and ITS-2 datasets, marker biases were observed, which suggests that multiple barcodes provide better overall representation of mycobiomes.

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Abstract

Global warming will most likely lead to increased drought stress in forest trees. We wanted to describe the adaptive responses of fine roots and fungal hyphae, at different soil depths, in a Norway spruce stand to long-term drought stress induced by precipitation exclusion over two growing seasons. We used soil cores, minirhizotrons and nylon meshes to estimate growth, biomass and distribution of fine roots and fungal hyphae at different soil depths. In control plots fine roots proliferated in upper soil layers, whereas in drought plots there was no fine root growth in upper soil layers and roots mostly occupied deeper soil layers. Fungal hyphae followed the same pattern as fine roots, with the highest biomass in deeper soil layers in drought plots. We conclude that both fine roots and fungal hyphae respond to long-term drought stress by growing into deeper soil layers.

Abstract

Ash dieback, caused by the ascomycete Hymenoscyphus fraxineus, has been spreading throughout Europe since the early 1990s, threatening European ash at a continental scale. Little is known about the development of the disease in individual forest trees and in different age classes. In this study we monitored ash dieback on trees of different diameter classes in five permanent plots in ash stands in south-eastern Norway from 2009 to 2016, and from 2012 to 2016 in three plots in western Norway with a shorter disease history. Our results showed that more than 80% of the youngest and more than 40% of the intermediate future crop trees in the plots in south-eastern Norway were dead by 2016, while the disease development in large, dominant trees was slower. Although less damage has been observed in the plots in western Norway, the trend for the juvenile trees is the same as in south-eastern Norway with rapidly increasing damage and mortality. Most dead trees in south-eastern Norway were found at sites with high soil moisture and showed symptoms of root-rot caused by Armillaria species. Infected trees, both young and old ones, are weakened by the disease and appear to be more susceptible to other, secondary pathogens, especially under unfavourable site conditions.

Abstract

Modified wood can provide protection against a range of wood deteriorating organisms. Several hypotheses have been put forward regarding the protection mechanisms against wood decaying fungi including fungal enzyme inefficiency due to non-recognition, lower micropore size, and insufficient wood moisture content. The aim of this study was to obtain new insight into the protection manner of furfuryl alcohol (FA) modified Scots pine sapwood (WFA), and to examine biochemical mechanisms and adaptive changes in gene expression utilised by Postia placenta during early colonisation of WFA. Samples were harvested after 2, 4, and 8 weeks of incubation. After 8 weeks, the mass loss (0.1%) and wood moisture content (21.0%) was lower inWFA, than in non-modified Scots pine sapwood samples (W), 26.1% and 46.1%, respectively. Microscopy revealed needle-shaped calcium oxalate crystals, at all harvesting points, most prominently present after 4 and 8 weeks, and only in the WFA samples. Among the findings based on gene profiles were indications of a possible shift toward increased expression, or at least no down regulation, of genes related to oxidative metabolism and concomitant reduction of several genes related to the breakdown of polysaccharides in WFA compared to W.

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Abstract

Ten saplings of European ash (Fraxinus excelsior L.) naturally infected by the invasive ash dieback pathogen Hymenoscyphus fraxineus were collected in Ukraine and Norway and examined for bark necrosis and extension of discoloration in sapwood and pith in a stem region. Tissue-specific colonization profiles were determined by spatial analyses of symptomatic and visually healthy stem tissues using a H. fraxineus-specific qPCR assay and light microscopy. Our data suggest that hyphal growth in the starch-rich perimedullary pith is of particular importance for both axial and radial spread of H. fraxineus, but that most of its biomass accumulates in sapwood parenchyma. The study confirms the results from earlier work and presents new information that refines the current stem invasion model.

Abstract

Pythium species are fungal-like organisms distributed all over the world. Most Pythium spp. live as saprophytes, but some of them are pathogenic. Here we report on disease incidence in Norway spruce (Picea abies) seedlings caused by Pythium undulatum, and pathogenicity in vitro of Norwegian isolates of P. undulatum and P. anandrum.

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Abstract

Trees must respond to many environmental factors during their development, and light is one of the main stimuli regulating tree growth. Thinning of forest stands by selective tree removal is a common tool in forest management that increases light intensity. However, morphological and anatomical adaptations of individual shoots to the new environmental conditions created by thinning are still poorly understood. In this study, we evaluated shoot morphology (shoot length, needle number, projected leaf area) and anatomy (tracheid lumen area, tracheid number, tracheid dimensions, xylem area, potential hydraulic conductivity) in three Norway spruce (Picea abies/L./Karst.) families exposed to different thinning regimes. We compared shoot characteristics of upper-canopy (i.e. sun-exposed) and lower-canopy (i.e. shaded) current-year shoots in a control plot and a plot thinned to 50 % stand density the previous year. One tree per family was chosen in each treatment, and five shoots were taken per canopy position. We found that upper-canopy shoots in both plots had higher values than lower-canopy shoots for all studied parameters, except lumen roundness and tracheid frequency (i.e. tracheid number per xylem area). Thinning had little effect on shoot morphology and anatomy 1 year after thinning, except for small but significant changes in tracheid dimensions. Needles were more sensitive to altered light conditions, as projected leaf area of shoot, needle number and leaf hydraulic conductivity changed after thinning. Differences between upper- and lower-canopy shoots did not seem to be influenced by thinning and were almost the same in both plots. Our results suggest that lower-canopy shoots require several years to modify their morphology and anatomy to new light conditions following thinning. The slow light adaptation of the lower canopy may be of practical importance in forest management: thinned stands may be predisposed to drought stress because newly exposed shoots experience increased illumination and transpiration after thinning.

Abstract

Local climate conditions have a major influence on the biological decomposition of wood. To examine the influence of different temperature regimes on wood decay caused by the brown rot fungus Postia placenta in wood with differing natural durability, sapwood (sW) and heartwood (hW) of Scots pine, inoculated mini-blocks were incubated for up to 10 weeks at temperatures conducive or above optimal to wood decay. We profiled mass loss (ML) and wood composition, and accompanying changes in wood colonization and transcript level regulation of fungal candidate genes. The suppressive effect of suboptimal temperature on wood decay caused by P. placenta appeared more pronounced in Scots pine hW with increased durability than in sW with low decay resistance. The differences between sW and hW were particularly pronounced for cultures incubated at 30°C: unlike sW, hW showed no ML, poor substrate colonization and marker gene transcript level profiles indicating a starvation situation. As brown rot fungi show considerable species-specific variation in temperature optima and ability to mineralize components that contribute to wood durability, interactions between these factors will continue to shape the fungal communities associated to wood in service.

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Abstract

Purpose: Drought-induced tree susceptibility is a major risk associated with climate change. Here we report how an 11-week drought affected tracheid structure, gene expression, and above- and belowground growth in 5-year-old Norway spruce trees (Picea abies) under controlled conditions. Results: The canopy of trees subjected to severe drought had significantly less current-year needle biomass, and fewer tracheids and tracheid rows in current-year shoots compared to fully watered control trees. Belowground tissues were more strongly affected by drought than aboveground tissues. In fine roots (<2 mm diameter) severe drought significantly reduced root biomass, root diameter, root length density and root surface area per soil volume compared to the control. Tracheid diameter and hydraulic conductivity in fine roots were significantly lower and tracheid flatness higher in trees subjected to severe drought than in control trees, both for long and short roots. Transcripts of the drought-related dehydrins PaDhn1 and PaDhn6 were strongly upregulated in stem bark and current-year needles in response to drought, whereas PaDhn4.5 was down-regulated. Conclusions: This study demonstrates that drought reduces biomass and hydraulic conductivity in fine roots and needles. We suggest that the ratio between PaDhn6 and PaDhn4.5 may be a sensitive marker of drought stress in Norway spruce.

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Abstract

Purpose: To identify the key parameters involved in cereal starch digestion and associated glycaemic response by the utilisation of a dynamic gastro-duodenal digestion model. Methods: Potential plasma glucose loading curves for each meal were calculated and fitted to an exponential function. The area under the curve (AUC) from 0 to 120 min and total digestible starch was used to calculate an in vitro glycaemic index (GI) value normalised against white bread. Microscopy was additionally used to examine cereal samples collected in vitro at different stages of gastric and duodenal digestion. Results: Where in vivo GI data were available (4 out of 6 cereal meals) no significant difference was observed between these values and the corresponding calculated in vitro GI value. Conclusion: It is possible to simulate an in vivo glycaemic response for cereals when the gastric emptying rate (duodenal loading) and kinetics of digestible starch hydrolysis in the duodenum are known.

Abstract

The outcome of a compatible mycorrhizal interaction is different from that in a compatible plant–pathogen interaction; however, it is not clear what mechanisms are used to evade or suppress the host defence. The aim of this work is to reveal differences between the interaction of Norway spruce roots to the pathogen Ceratocystis polonica and the ectomycorrhizal Laccaria bicolor, examine if L. bicolor is able to evade inducing host defence responses typically induced by pathogens, and test if prior inoculation with the ectomycorrhizal fungus affects the outcome of a later challenge with the pathogen. The pathogen was able to invade the roots and caused extensive necrosis, leading to seedling death, with or without prior inoculation with L. bicolor. The ectomycorrhizal L. bicolor colonised primary roots of the Norway spruce seedlings by partly covering, displacing and convoluting the cells of the outer root cortex, leaving the seedlings healthy. We detected increased total peroxidase activity, and staining indicating increased lignification in roots as a response to C. polonica. In L. bicolor inoculated roots there was no increase in total peroxidase activity, but an additional highly acidic peroxidase isoform appeared that was not present in healthy roots, or in roots invaded by the pathogen. Increased protease activity was detected in roots colonised by C. polonica, but little protease activity was detected in L. bicolor inoculated roots. These results suggest that the pathogen efficiently invades the roots despite the induced host defence responses, while L. bicolor suppresses or evades inducing such host responses in this experimental system.

Abstract

This chapter provides an overview of anatomical and ecological aspects of resin-based defences in pines and contrasts the defence strategy of pines with that of other conifers. The main constituents of conifer resin are mono- and diterpenes in about equal amounts, with smaller amounts of sesquiterpenes. Resin production and storage represent a great cost for the trees, and because resin is both chemically toxic and physically deterring to insects and pathogens it has long been considered an important defence mechanism in conifers. Preformed or constitutive resin structures are present in pines and all other members of the pine family, but are generally absent in non-Pinaceae species. Resin stored under pressure in constitutive ducts flows out when a tree is injured and helps trapping or repelling invading organisms and sealing the wound. Pines have constitutive resin ducts in needles, phloem and xylem. In the phloem and xylem constitutive resin ducts are oriented both radially (within the radial rays) and axially in the form of cortical resin ducts in the outer phloem and constitutive resin ducts in the xylem. Numerous connections between the radial resin ducts and the axial resin ducts in the xylem create a large inter-connected resin reservoir. In addition, so-called traumatic resin ducts can be induced axially in the xylem in response to wounding, insect attack or other biotic and abiotic stresses. Traumatic resin ducts may contribute to so-called acquired or systemic induced resistance that increases tree resistance to future attacks.

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Abstract

Conifer needles are extraordinarily variable and much of this diversity is linked to the water transport capacity of the xylem and to xylem conduit properties. However, we still know little about how anatomical characteristics influence the hydraulic efficiency of needle xylem in different parts of the crown. In this study we evaluated needle function and anatomy in Norway spruce families exposed to different light conditions. We measured tracheid and needle characteristics of sun-exposed and shaded current-year needles in two experimental plots: a control plot and a thinned plot with 50% reduction in stand density. Sun-exposed needles had a larger tracheid lumen area than shaded needles, and this was caused by a larger maximum tracheid lumen diameter, while the minimum lumen diameter was less plastic. Sun-exposed needles had also higher theoretical hydraulic conductivity than shaded needles. Thinning leads to increased radiation to the lower branches, and presumably exposes the upper branches to stronger water stress than before thinning. Thinning affected several needle parameters both in sun-exposed and shaded needles; tracheid lumens were more circular and minimum tracheid lumen diameter was larger in the thinned plot, whereas maximum tracheid lumen diameter was less plastic on both plots. This study demonstrates that needle xylem structure in Norway spruce is clearly influenced by the light gradient within the tree crown.

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Abstract

Norway spruce (Picea abies) bark contains specialized phloem parenchyma cells that swell and change their contents upon attack by the bark beetle Ips typographus and its microbial associate, the blue stain fungus Ceratocystis polonica. These cells exhibit bright autofluorescence after treatment with standard aldehyde fixatives, and so have been postulated to contain phenolic compounds. Laser microdissection of spruce bark sections combined with cryogenic NMR spectroscopy demonstrated significantly higher concentrations of the stilbene glucoside astringin in phloem parenchyma cells than in adjacent sieve cells. After infection by C. polonica, the flavonoid (+)-catechin also appeared in phloem parenchyma cells and there was a decrease in astringin content compared to cells from uninfected trees. Analysis of whole-bark extracts confirmed the results obtained from the cell extracts and revealed a significant increase in dimeric stilbene glucosides, both astringin and isorhapontin derivatives (piceasides A to H), in fungus-infected versus uninfected bark that might explain the reduction in stilbene monomers. Phloem parenchyma cells thus appear to be a principal site of phenolic accumulation in spruce bark.

Abstract

Pathogen challenge of tree sapwood induces the formation of reaction zones with antimicrobial properties such as elevated pH and cation content. Many fungi lower substrate pH by secreting oxalic acid, its conjugate base oxalate being a reductant as well as a chelating agent for cations. To examine the role of oxalic acid in pathogenicity of white-rot fungi, we conducted spatial quantification of oxalate, transcript levels of related fungal genes, and element concentrations in heartwood of Norway spruce challenged naturally by Heterobasidion parviporum. In the pathogen-compromised reaction zone, upregulation of an oxaloacetase gene generating oxalic acid coincided with oxalate and cation accumulation and presence of calcium oxalate crystals. The colonized inner heartwood showed trace amounts of oxalate. Moreover, fungal exposure to the reaction zone under laboratory conditions induced oxaloacetase and oxalate accumulation, whereas heartwood induced a decarboxylase gene involved in degradation of oxalate. The excess level of cations in defense xylem inactivates pathogen-secreted oxalate through precipitation and, presumably, only after cation neutralization can oxalic acid participate in lignocellulose degradation. This necessitates enhanced production of oxalic acid by H. parviporum. This study is the first to determine the true influence of white-rot fungi on oxalate crystal formation in tree xylem.

Abstract

Heterobasidion parviporum, a common pathogenic white-rot fungus in managed Norway spruce forests in northern and central Europe, causes extensive decay columns within stem heartwood of the host tree. Infected trees combat the lateral spread of decay by bordering the heartwood with a fungistatic reaction zone characterized by elevated pH and phenol content. To examine the mode of fungal feeding in the reaction zone of mature Norway spruce trees naturally infected by H. parviporum, we conducted spatial proWling of pectin and hemicellulose composition, and established transcript levels of candidate fungal genes encoding enzymes involved in degradation of the diVerent cell wall components of wood. Colonized inner heartwood showed pectin and hemicellulose concentrations similar to those of healthy heartwood, whereas the carbohydrate proWles of compromised reaction zone, irrespective of the age of fungal activity in the tissue, indicated selective fungal utilization of galacturonic acid, arabinose, xylose and mannose. These data show that the rate of wood decay in the reaction zone is slow. While the up-regulation of genes encoding pectinases and hemicellulases preceded that of the endoglucanase gene during an early phase of fungal interaction with xylem defense, the manganese peroxidase gene showed similar transcript levels during diVerent phases of wood colonization. It seems plausible that the reaction zone components of Norway spruce interfere with both lignin degradation and the associated co-hydrolysis of hemicelluloses and pectin, resulting in a prolonged phase of selective decay.

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Abstract

Conifers and other trees are constantly adapting to changes in light conditions, water/nutrient supply and temperatures by physiological and morphological modifications of their foliage. However, the relationship between physiological processes and anatomical characteristics of foliage has been little explored in trees. In this study we evaluated needle structure and function in Norway spruce families exposed to different light conditions and transpiration regimes. We compared needle characteristics of sun-exposed and shaded current-year needles in a control plot and a thinned plot with 50% reduction in stand density. Whole-tree transpiration rates remained similar across plots, but increased transpiration of lower branches after thinning implies that sun-exposed needles in the thinned plot were subjected to higher water stress than sun-exposed needles in the control plot. In general, morphological and anatomical needle parameters increased with increasing tree height and light intensity. Needle width, needle cross-section area, needle stele area and needle flatness (the ratio of needle thickness to needle width) differed most between the upper and lower canopy. The parameters that were most sensitive to the altered needle water status of the upper canopy after thinning were needle thickness, needle flatness and percentage of stele area in needle area. These results show that studies comparing needle structure or function between tree species should consider not only tree height and light gradients, but also needle water status. Unaccounted for differences in needle water status may have contributed to the variable relationship between needle structure and irradiance that has been observed among conifers.

Abstract

In field experiments, clones of Norway spruce [Picea abies (L.) Karst.] showed different degrees of resistance against pathogenic fungi inoculated into the bark that correlate with differences in polyphenolic parenchyma (PP) cells of the bark. Cells of spruce callus cultures, particularly towards the callus surface, resemble PP cells and this study looks at changes in callus cells during infection and the relative resistance of cultures from clones of low (weak) or high (strong) resistance to fungal infection. Callus cultures, initiated from trees with different resistance, were co-inoculated with Ceratocystis polonica (Siem.) C. Moreau and Heterobasidion annosum (Fr.) Bref. Callus cells from strong clones resemble PP cells of bark tissue from strong clones, having more polyphenolic bodies, while callus cells from weak clones are more similar to PP cells from those clones, which have less extensive phenolic bodies. Callus cultures from trees with weak resistance were more quickly overgrown by both species of pathogenic fungi than cultures from trees with strong resistance. Callus cells of infected cultures showed changes similar to activated PP cells of bark, including enhanced accumulation of polyphenolics. Phenolic bodies were more numerous and more extensive (larger and denser) in callus cells of strong versus weak clones under all conditions. Thus, callus cells may perform similar functions in defense as PP cells in the bark. Callus from trees of varying resistance seem to reflect the relative resistance of the trees from which they are derived, and this study indicates that some mechanisms of resistance can be studied using callus from trees of different resistance.

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Abstract

Polyphenolic parenchyma cells (PP cells) in Norway spruce (Picea abies (L.) Karst.) stem phloem play important roles in constitutive and inducible defenses. To determine whether anatomical and molecular changes in PP cells are correlated with tree resistance, we infected two Norway spruce clones with the pathogenic fungus Ceratocystis polonica (Siem.) C. Moreau. The fungus induced significantly different lesion lengths in the two clones, indicating that one clone was more resistant to the fungus (short lesions) than the other (long lesions). After infection, the cross-sectional area of PP cells and their vacuolar polyphenol bodies increased in the three most recent annual rings of PP cells in both clones. The more resistant clone had larger PP cells with denser polyphenol bodies than the less resistant clone, whereas the less resistant clone accumulated relatively more polyphenols after infection. Compared with the less resistant clone, the more resistant clone contained higher starch concentrations before infection that were reduced more quickly after infection before returning to original values. Low transcript levels of chalcone synthase were detected in uninfected tissues of both clones, but the levels increased dramatically after infection. Transcript levels were higher and peaked 6 days earlier in the more resistant clone than in the less resistant clone. The activity of at least one highly basic peroxidase isoform was greatly enhanced after infection, and this increase occurred earlier in the more resistant clone.

Abstract

Introduction: Survival and competitive successes of boreal forest trees depend on a balance between exploiting the full growing season and minimising frost injury through proper timing of hardening in autumn and dehardening in spring. Our research indicates that the female parents of Norway spruce adjust these timing events in their progeny according to the prevailing temperature conditions during sexual reproduction. Reproduction in a cold environment advances bud-set and cold acclimation in the autumn and dehardening and flushing in spring, whereas a warm reproductive environment delays these progeny traits by an unknown non-Mendelian mechanism. We are now looking for molecular mechanisms that can explain this “epigenetic” phenomenon. Material and methods: We have performed identical crosses with the same Norway spruce (Picea abies) parent, as discussed by Skrøppa & Johnsen (1994) and Johnsen et al. (1995), in combination with timed temperature treatments during shorter and longer periods from female meiosis, pollen tube growth, syngamy and embryogenesis and tested the progenies for bud-set and frost hardiness. We have followed the transcription of the spruce phytochromes PHYO, PHYP and PHYN and the class IV chitinase PaChi4 using Quantitative Multiplex Real-Time PCR. Results and conclusions: The effect of temperature on Adaptive properties is most likely a response to accumulated heat during embryogenesis and seed maturation. Our first attempt to look for a molecular mechanism has revealed that transcription of PHYO, PHYP and PHYN and the class IV chitinase PaChi4 (relative to alphaTubulin) all show higher transcription levels in progenies born under cold conditions than their full-sibs born under warmer conditions. This result is consistent with preliminary findings that methylation of cytosine in total DNA is higher in progenies reproduce under warm conditions than their colder full-sib counterparts. If these observations are related to methylation or other epigenetic effects, we may explain why progenies with a memory of a past time cold embryogenesis are more sensitive to short days than their full-sibs with a warmer embryonic history.

Abstract

Research indicate that the female parents of Norway spruce adjust these timing events in their progeny according to the prevailing temperature conditions during seed development. Reproduction in a cold environment advances bud-set and cold acclimation in the autumn and dehardening and flushing in spring, whereas a warm reproductive environment delays these progeny traits by an unknown non-Mendelian mechanism. We have performed identical crosses in combination with timed temperature treatments during shorter and longer periods from female meiosis, pollen tube growth, syngamy and embryogenesis, tested the progenies for bud-set and frost hardiness, and concluded that the effect of temperature most likely is a response to accumulated heat during embryogenesis and seed maturation. Our first attempt to look for a molecular mechanism has revealed that transcription of PHYO, PHYP and PHYN and the class IV chitinase PaChi4 (using RealTime PCR) all show higher transcription levels in progenies born under cold conditions than their full-sibs born under warmer conditions. This result is consistent with preliminary findings that methylation of cytosine in total DNA is higher in progenies reproduce under warm conditions than their colder full-sib counterparts. If these observations are related to methylation, we may explain why progenies with a memory of a past time cold embryogenesis are more sensitive to short days than their full-sibs with a warmer embryonic history.