The effect of nitrogen fertilization on fungistatic phenolic compounds in roots of beech (Fagus sylvatica) and Norway spruce (Picea abies)

The effect of nitrogen fertilization on fungistatic phenolic compounds in fine roots of beech and Norway spruce growing in afforestation plots was analysed. The plots were situated at two sites in Switzerland on acidic soil with low base saturation. For 9 years, the trees have been treated with dry ammonium nitrate to give 0, 10, 20, 40, 80, 160 kg N ha^?1 year^?1, respectively. The phenolic compounds responded differently to fertilization. Fine roots of beech showed a significant decrease of (?)‐epicatechin and piceatannol with increasing nitrogen fertilization. The concentration of protocatechuic acid was increased with fertilization. Roots of fertilized Norway spruce showed significantly decreased concentrations of 4‐hydroxyacetophenone and piceatannol. The mycelial growth of three isolates each of Heterobasidion annosum s.l. and Cylindrocarpon destructans was tested on agar media containing various phenolic compounds in concentrations found in fine roots of Norway spruce (Picea abies) and beech (Fagus sylvatica). All three H. annosum isolates were inhibited by p‐coumaric acid and (?)‐epicatechin. Two isolates were inhibited by another four phenolic compounds (p‐hydroxybenzoic acid, 4‐hydroxyacetophenone, piceatannol and protocatechuic acid), one by (+)‐catechin. Two of three C. destructans isolates were inhibited by all phenolic compounds except for (+)‐catechin which affected only one isolate, one isolate did not respond at all.     

Controlling and predicting the spread of heterobasidion annosum from infected stumps and trees of picea abies

Two Norway spruce stands with heavy infections of Heterobasidion annosum were clear‐cut in 1957 and 1959 in Sweden. The stumps were extracted, the soil sifted to remove most of the roots, and young Norway spruce were planted. After 25 and 28 years, H. annosum had infected 1 % and 2% of trees on plots where stumps had been removed and 17 % and 12% of the trees on control plots, respectively. Several of the H. annosum clones fruiting on old‐growth stumps were also detected in decayed, standing trees. The same fungal clone was found to be infecting adjacent trees from several old‐growth stumps. In addition to old stumps, stumps from recent thinnings and diseased living trees were traced as infection sources. Their relative importance in spreading disease was estimated. Disease risk predictions based on the distance of a tree from various infection sources correlated well with observed frequencies of rot.     

Intersterilitätsgruppen und Klone von Heterobasidion annosum-Isolaten aus Koniferen- Wurzel- und -Stammfäulen

Intersterility groups and clones of Heterobasidion annosum isolates from root and butt rots of conifers 69 H. annousum heterokaryons from scots pine, Douglas fir, Norway spruce and larch belonged to the P group, three heterokaryons from Norway spruce to the S group. The results of a study with clones of H. annosum isolates from roots of Scotch pine trees in close neighbourhood suggest colonisation by H. annosum (partly) via root contacts.     

Intraspecific variation in Heterobasidion annosum for growth in sapwood of Picea abies and Pinus sylvestris

Two greenhouse experiments were conducted to study intraspecific variation in growth of the root rot fungus Heterobasidion annosum in living host sapwood. In experiment 1, Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) seedlings were inoculated with H. annosum isolates, 14 each of the S-and P-intersterility groups, collected from various parts of Sweden. In pine, the P-group isolates were more virulent than the S-group isolates both in terms of infection frequency, induced mortality rate (p < 0.05), and fungal growth in sapwood (p < 0.05). In spruce, the P-group isolates were also more virulent on average, but the difference was not statistically significant. Both S and P isolates had a higher infection frequency and a significantly longer sapwood growth on spruce than on pine. The P-group caused higher mortality on pine than on spruce. The length of the lesion in the inner bark was strongly correlated with fungal growth in spruce, but not in pine where the lesions were short or absent. In experiment 2, ten Norway spruce clones were inoculated with 18 S-isolates, originating from nine live-decayed trees and from nine spore-infected stumps in a single Norway spruce stand. The objective was to test whether any selection for growth rate in sapwood was detectable among individuals of H. annosum originating either from stumps or trees. The results gave no support for such selection since no difference in sapwood growth between the two groups of isolates was found.     

The spreading of the S type of Heterobasidion annosum from Norway spruce stumps to the subsequent tree stand

The occurrence of Heterobasidion annosum in stumps and growing trees was investigated on 15 forest sites in southern Finland where the previous tree stand had been Norway spruce (Picea abies) infected by H. annosum, and the present stand was either Scots pine (Pinus sylvestris), lodgepole pine (Pinus contorta), Siberian larch (Larix siberica), silver birch (Betula pendula) or Norway spruce 8–53 years old. Out of 712 spruce stumps investigated of the previous tree stand, 26.3% were infected by the S group and 0.3% by the P group of H. annosum. The fungus was alive and the fruit bodies were active even in stumps cut 46 years ago. In the subsequent stand, the proportion of trees with root rot increased in spruce stands and decreased in stands of other tree species. On average, one S type genet spreading from an old spruce stump had infected 3.0 trees in the following spruce stand, 0.5 trees in lodgepole pine, 0.3 trees in Siberian larch, 0.05 trees in Scots pine and 0.03 trees in silver birch stand. Although silver birch generally was highly resistant to the S type of H. annosum, infected trees were found on one site that was planted with birch of a very northern provenance.     

Intersterilitätsgruppen und Klone von Heterobasidion annosum in einem 31jährigen Fichtenbestand1

Intersterility groups and clones of Heterobasidion annosum in a 31 years old Norway spruce stand . H. annosum isolates from roots of 13 spruce trees growing in close neighbourhood be longed to the P group (from five roots) and to the S group (from 44 roots). The clone identifications revealed colonisation via root contacts.     

Response of Compensatory-Fertilized Pinus sylvestris to Infection by Heterobasidion annosum

The effects of compensatory fertilization on the infection and growth rate of Heterobasidion annosum were studied in a 40-yr-old, naturally regenerated Scots pine (Pinus sylvestris L.) stand in south-eastern Finland. The treatments were: (1) unfertilized control, (2) a compound fertilizer containing P, K, Ca, Mg, S, Cu, Zn and B, (3) as treatment 2 but with nitrogen, (4) as treatment 3 but with limestone, (5) a mixture of nitrogen and limestone composed on the basis of needle analysis, and (6) wood ash. Pine roots were inoculated on two occasions four and five growing seasons after fertilization using four different strains of the P type of H. annosum. Two years after inoculation, the fungus was alive in 28.9% of the 135 inoculated roots. Fungus survival was highest in the control trees (50%) and poorest in the treatments 2 and 3 (10.5% and 16.7%, respectively). These two treatments differed significantly from the control. Total mycelial extension during the 2-yr study period was 16.4, 2.1, 4.5, 18.1, 15.2 and 5.3 cm in treatments 1, 2, 3, 4, 5 and 6, respectively. Only treatment 2 differed significantly from the control (p<0.05, df=23). The result suggests that the application of slow-release compound fertilizers without supplementary limestone may increase the resistance of Scots pine to infection by H. annosum. The nitrogen-free compound fertilizer may also retard the spread of annosum root rot in infected pine stands.     

Susceptibility of Sitka spruce and grand fir trees to decay by Heterobasidion annosum

The susceptibility of Sitka spruce (Picea sitchensis) and grand fir (Abies grandis) to decay by Heterobasidion annosum was compared on a site with a previous history of serious disease. The incidence of decay 15–16 years after planting was 1.5% in grand fir, compared with 34.8% in Sitka spruce. These results are broadly similar to those reported from other trials. More information is required for older trees in Britain but the evidence so far available suggests that grand fir is more resistant to H. annosum than Sitka spruce. Planting grand fir on severely infested sites may therefore significantly reduce the serious losses that could be expected with Sitka spruce. In 14 out of 271 decayed Sitka spruce H. annosum was absent from the middle or base of the decay column but present at the top. Approximately 3% of infected spruce showed features suggesting some degree of resistance. Resin bleeding was observed at the base of 23.2% of the infected spruce, and the mean height of the decay column in these trees was significantly greater (0.96 m) than in those without this feature (0.66 m). The inoculum for infection was provided by stumps of the previous crop, and the genets of H. annosum that were present in some infected trees were also identified in stumps. The majority of infected trees contained only a single genet but three trees contained two genets. In this young crop individual genets were smaller than those found elsewhere; the largest extended to include six trees.     

Resinicium bicolor; a potential biological control agent for Heterobasidion annosum

After introductory competition tests in the laboratory, Resinicium bicolor was used as a potential control agent for the conifer root rot fungus Heterobasidion annosum. Greenhouse pathogenicity tests with R. bicolor on 4-year-old seedlings of Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) showed moderate incidence of infection. In three places in Sweden, four test areas were chosen for field experiments in first-rotation plantations and also in old forest sites of Norway spruce. Wood blocks, pre-inoculated with one strain of R. bicolor, were buried in the soil beside stumps at 0, 1, 2, 3 and 4 months after thinning using various spatial designs. In two of the test areas, half of the stumps were treated with a suspension of H. annosum conidia from one strain by surface spraying. After 2–3 years, stump roots were investigated and the length of growth of both species were noted. The identity of mycelia reisolated from and wood debris in the test areas were confirmed by somatic compatibility tests with the original strains. The strain of R. bicolor released was recovered from all over the test area; the released H. annosum strain was only reisolated from the conidia sprayed stump roots. R. bicolor had little effect on the growth and occurrence of H. annosum. Potential control of disease spread may arise, however, from occlusion of the pathogen from outer parts of roots.     

Urea treatment reduced Heterobasidion annosum s.l. root rot in Picea abies after 15 years

Stump protection using chemical or biological agents is the main control measure against root and butt rot caused by Heterobasidion annosum s.l. in northern and temperate conifer forests. Long-term effects of urea treatment of stumps are poorly known and here we describe a 15-year study of urea treatment on the rot incidence on Norway spruce (Picea abies). We also tested the effect of urea protection on tree growth and on the resistance of stands against strong winds. Four treatments were made in two replications in two first-rotation P. abies stands in southern Sweden; after first-thinning stumps were (i) treated with urea 35% (w/v), (ii) artificially infected with H. annosum conidia, (iii) half urea treated and half artificially conidia infected, (iv) untreated, therefore naturally infected. After 15 years, the trees were sampled at 20 cm above ground using an increment borer and observed for presence of rot and, following incubation, presence of H. annosum conidia. Tree growth was calculated by measuring the diameter before and after the treatment. Urea treated plots showed the lowest incidence of rot (3%) as well as of H. annosum incidence (0%). Conidia treatment showed the highest incidence of rot (68%), its incidence was higher than that observed in natural infection treatment (43%), but did not differ from that of the 50% conidia treatment (47%). On about 30% of the rotted trees we observed conspicuous H. annosum fruiting. We did not observe growth reduction associated with tree rot. H. annosum was the only fungus observed associated with rotted trees which suggest that it was responsible for most of the rot observed in the investigated plots. Urea treated plots showed the lowest incidence of windthrown trees, and 59% of the windthrown tree incidence among the plots was explained by the incidence of H. annosum. Urea can be regarded as a reliable long-term protection method against root and butt rot of Norway spruce.     

Induced resistance of Norway spruce,variation of phenolic compounds and their effects on fungal pathogens

Three clones of Norway spruce (Picea abies) were studied for their response to mass‐inoculation with the blue‐stain fungus Ceratocystis polonica. The effect of different pretreatments (fungal inoculation and wounding) before mass‐inoculation was investigated for their possible role in an acquired resistance reaction. Pretreated trees showed enhanced resistance to the subsequent mass‐inoculation relative to control trees that received no pretreatment. Furthermore, the fungal colonization of inoculated trees was less than that of wounded trees. The phenolic content of the bark, analysed by RP‐HPLC, was compared in trees receiving different treatments. Trees inoculated with C. polonica had higher average concentration of (+)‐catechin, taxifolin and trans‐resveratrol than wounded trees. Both inoculated and wounded trees had higher average concentrations of these compounds than control trees. The effect of the phenolic extract of Norway spruce bark on the growth of the root rot fungus Heterobasidion annosum and the blue‐stain fungi C. polonica and Ophiostoma penicillatum were investigated in vitro. Heterobasidion annosum was not negatively affected, and the extracts had fungistatic effects on the blue‐stain fungi. The growth of O. penicillatum was more inhibited than the growth of the more aggressive C. polonica.     

Modelling the incidence of Heterobasidion annosum butt rots and related economic losses in alpine mixed naturally regenerated forests of northern Italy

A total of 2257 recently felled stumps were sampled from 22 mixed naturally regenerated forest stands in the Aosta Valley, western Italian Alps, and examined for Heterobasidion annosum butt rots. Disease incidence ranged from 6% to 71% depending on sites, and H. annosum accounted for 92% of the total number of diseased stumps. H. annosum incidence was significantly higher (Chi‐squared multiple comparison tests, p < 0.05) on Norway spruce (44%) than on the other tree species (silver fir = 18%, larch = 12% and Scots pine = 6%). Based on the information on the airborne inoculum composition of the fungus, all the three European species of H. annosum were present, with a variable frequency, depending on site. A partial least squares regression analysis showed that the relative abundance of Norway spruce and four variables describing the size of trees were the best predictors for the incidence of H. annosum butt rots. A model having these variables as predictors was developed (r² = 0.75; p < 0.001) and successfully validated on five additional forest stands. An estimate of the losses in yield and value of timber associated with the disease, i.e. direct losses, was also carried out in the forests included in the survey. The percentage of direct financial losses was either comparable or lower than the average level of disease incidence.     

In vitro interactions between bacteria isolated from Sitka spruce stumps and Heterobasidion annosum

Culture medium composition affected antagonism by bacterial isolates from Sitka spruce (Picea sitchensis) stumps against Heterobasidion annosum. Fifty percent of bacterial isolates inhibited H. annosum growth on sporulation agar or yeast–dextrose–peptone agar; only 10% of isolates caused inhibition on both media. Proportions of isolates inhibiting H. annosum varied with stump age; fewer isolates from 4‐ or 6‐year‐old stumps exhibited antagonism than isolates from older or younger stumps. Fifteen isolates showing antagonism on sporulation agar were tested against H. annosum in spruce wood cubes. None of the bacterial isolates alone caused a significant weight reduction in inoculated cubes. Relative inoculation times of bacterial isolates and H. annosum had an effect on weight loss in interactions; simultaneous inoculation with isolates and H. annosum inhibited weight loss caused by H. annosum compared with bacteria‐free controls. Inoculation with bacterial isolates 10 days before H. annosum had no effect on the decay rate. In contrast, inoculation with H. annosum 10 days before bacteria increased weight loss of cubes by 200% relative to cultures lacking bacteria. The effect of a mixed bacterial inoculum on weight change in 0.2‐mm spruce wood slips co‐inoculated with H. annosum, Resinicium bicolor, Hypholoma fasciculare, Stereum sanguinolentum or Melanotus proteus differed between different fungi.     

Early infection by Heterobasidion annosum in Larix x eurolepis seedlings planted on infested sites

The incidence of Heterobasidion annosum was examined in three young hybrid larch (Larix × eurolepis) plantations in southern Sweden that were established after felling Norway spruce (Picea abies) stands heavily infected by the fungus. The incidence of H. annosum was 7 %, 33 %, and 70 %, respectively, in the 2-, 3-, and 5-year-old plantations. In all plantations, H. annosum was the most frequent rot-causing fungus (81 %) and all isolates tested belonged to the P-intersterility group. No visible external differences between infected and healthy seedlings were found on any site. Both tap and lateral roots were infected by H. annosum. The results suggest that when hybrid larch is planted on sandy soils after clear felling of Norway spruce heavily infected by H. annosum, it is very susceptible to infection by H. annosum. Furthermore, transfer of H. annosum from infected stumps to hybrid larch occurs during the first few years after planting on scarified sites. In this study, scarification may have exacerbated the root disease situation and actually led to more early infections by distributing pieces inoculum across the sites.     

Signs and symptoms associated with Heterobasidion annosum and Armillaria ostoyae infection in dead and dying mountain pine (Pinus mugo ssp. uncinata)

Symptoms and signs associated with root rot caused by Heterobasidion annosum or Armillaria ostoyae in mountain pines (Pinus mugo ssp. uncinata) were investigated in the Swiss Alps. A sample of dying or recently dead mountain pine trees (≥12 cm d.b.h.) and saplings (<1.3 m height) was assessed for root pathogen infection by taking root samples followed by isolations in the laboratory. From a subsample, an additional core was taken from the butt of each tree and evaluated in the same fashion. A total of 157 dying or recently dead mountain pine trees and 184 saplings with roots infected by either of the two pathogens or which lacked infection were analyzed using logistic regression models. The main objectives were to determine the most prominent symptoms induced by the fungi (resinosis), signs of the fungi (mycelia, fruiting bodies and rhizomorphs), and tree characteristics (d.b.h./height and evidence of wounds) that would allow an easy and reliable determination of H. annosum and/or A. ostoyae infection of mountain pines in the field. Heterobasidion annosum caused both root and butt rot on mountain pine, whereas A. ostoyae was mostly restricted to the root systems of the trees sampled. The most discriminating sign for the presence of A. ostoyae infection was the presence of characteristic mycelial fans, and for H. annosum root rot the presence of H. annosum mycelia (sheets of paper‐thin mycelium and mycelial pustules). In addition, resinosis was a powerful predictor for A. ostoyae in trees. Symptoms and signs indicating A. ostoyae or H. annosum infections were more reliable for saplings than for mature trees. Armillaria rhizomorphs were not useful in detecting A. ostoyae infection and, if present, were often formed by saprophytic Armillaria species. Heterobasidion annosum fruiting bodies were rarely observed and poorly reflected the widespread occurrence of this pathogen in the mountain pine forests.     

Comparison of colonization capacity by asexual spores of Heterobasidion species in Norway spruce wood

Two species of the tree pathogenic fungus Heterobasidion spp. exist in Sweden, Heterobasidion annosum s.s. and Heterobasidion parviporum. Both species are known to infect Norway spruce (Picea abies). The aim of the study was to examine the interspecific competition between H. annosum s.s. and H. parviporum as well as their colonization rate in fresh Norway spruce wood. Equal amount of conidiospores from each species was sprayed together on 30 fresh, previously uninfected, Norway spruce billets. After incubation in a greenhouse, the proportion of Heterobasidion spp. colonies belonging to each species was recorded. Of the 196 colonies isolated from the upper part of billets, 195 were H. parviporum. All isolated colonies further down in the billets were H. parviporum. To study the colonization rate, H. annosum s.s. and H. parviporum were sprayed alone on 30 spruce billets each, incubated and growth recorded both vertically and horizontally. H. parviporum grew further down in the billets (p = 0.008) and covered a larger area (p < 0.001) than H. annosum s.s. While H. annosum s.s. and H. parviporum both infected fresh Norway spruce wood H. parviporum outgrew and outcompeted H. annosum s.s during the early colonization stage.     

Effects of repeated fertilization in young Norway spruce forests

Several studies have shown the positive effect of nitrogen fertilization on conifer growth. In young Norway spruce (Picea abies) stands, an additional effect of including a mixture of other nutrients has often, but not always, been found. We studied effects of repeated fertilization in 28 stands with young Norway spruce in central Norway. The treatments consisted of plots without nutrient addition (Control), fertilization with 150?kg?N?ha^?1 (150?N), and fertilization with 150?kg?N plus addition of P, K, Mg, B, Mn and Cu (150?N?+?mix), repeated three times with approximately eight years interval. There was a clear positive effect on volume increment of the 150?N and 150?N?+?mix treatments compared to Control, and the effect was significantly higher for 150?N?+?mix than for 150?N. Fertilization had a stronger effect in the first fertilization period than in the second, while the third period was intermediate. The effect of 150?N?+?mix was strongest at plots?>?300?m a.s.l. However, this correlation may be due to geological conditions rather than elevation. Further studies are needed to find out under which edaphic conditions a nutrient mixture will increase growth substantially in young spruce stands.     

Heterobasidion annosum root rot in Picea abies: Modelling economic outcomes of stump treatment in Scandinavian coniferous forests

Abstract

The economic outcomes of stump treatment against spore infections of the root rot pathogen Heterobasiodion annosum s. l. were analysed based on simulations in four stands typical of Swedish forestry and forest management: (A) Norway spruce [Picea abies (L.) Karst.] stand on former agricultural soil (SI?=?32), (B) Norway spruce stand (SI?=?26) on forest land; (C) Mixed stand of Norway spruce and Scots pine (Pinus sylvestris L.) (SI?=?24) with only H. parviporum present, i.e. no infection of Scots pine and no possibility of interspecies spread of disease between hosts; and (D) same as C, but H. annosum s. str. (Fr.) Bref and H. parviporum Niemelä & Korhonen present, i.e. interspecies spread of disease possible. Models for disease development, growth and yield and cross-cutting were used in the simulations. The simulated decay frequency in Norway spruce trees ranged between 2 and 90%. Stump treatment at the previous final felling and in all thinning operations was profitable at interest rates 1 and 3% in stands A, B and D, but not in stand C. In stand C, no stump treatment at all or treatment in thinnings only gave the highest net future value. Implications for stump treatment in practical forestry are discussed.     

Optimizing the management of a Picea abies stand under risk of butt rot

A simulation model was developed to predict the growth of a Norway spruce stand under risk of butt rot caused by Heterobasidion annosum stump infection and logging injuries. The simulation model was distance‐dependent; tree growth was predicted with a distance‐dependent model, and the spread of butt rot through root contacts depended on tree location. Infection of stumps and injured trees, and the spread of butt rot in the stand were stochastic processes whereas tree growth and mortality were treated as deterministic processes. The simulation model was used with the nonlinear optimization algorithm of ooke and J eeves (J. Assoc. Comput. Mach, 8, 212–229, 1961) to find the most profitable management schedule for an even‐aged, young stand. Optimization used four different stump infection rates and two spreading capacities from infected stumps. The profitability was evaluated by the expected soil expectation value (SEV) at a 3% interest rate. Two thinnings, both in winter‐time, and hence without H. annosum infections, resulted in the highest SEV. If any stump infection by H. annosum occurred, only one thinning and a shortened rotation were suggested. The optimal thinning rate tended to decrease but also large trees were removed with the increasing infection rate. With one thinning during a rotation, stump treatment was profitable above a stump infection rate of 10%     

A trial of disodium octaborate tetrahydrate for the control of Heterobasidion annosum

The extent of heartwood infection of Sitka spruce Picea sitchensis stumps following inoculation with basidiospores of Heterobasidion annosum was significantly reduced by application of 2% and 4% solutions of disodium octaborate tetrahydrate (DOT) immediately after felling. Infection of sapwood was so rare in all treatments, including controls, that the effectiveness of DOT in this tissue could not be judged. The results of this trial suggest that DOT may be toxic to H. annosum at lower levels of borate loading than previously thought possible. Over the 10 months of the experiment the borate loading in the stumps appeared to reach an equilibrium that was independent of the initial concentration applied. Stump-surface fruiting of Melanotus proteus, a potential fungal competitor of H. annosum, was not inhibited by these treatments.