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.     

Susceptibility to Heterobasidion parviporum in Picea abies clones grown in different environments

Thirty-five Norway spruce, Picea abies, clones from Sweden were tested for resistance to Heterobasidion parviporum. Rooted cuttings of the clones were planted in Italy and Greece and cultivated for two growing seasons before inoculation with H. parviporum. Extent of infection was determined 6 weeks later. The results were compared to those of earlier inoculations in Sweden. Plant growth traits were under strong genetic control in all locations with broad sense heritability estimates between 0.14 and 0.54. Lesion and fungal extension heritabilities were moderate, H² ranged from 0.09 to 0.20, and exhibited rather large genetic variation. There was significant genotypic correlation between Italy and Greece with respect to both lesions and fungal extension. No such correlations were found between Sweden and the two other countries. The lack of repeatability in testing susceptibility is unsatisfactory. It could be explained by C-effects associated with propagation of the host plants. Height growth correlated significantly and positively among all countries.     

Infection studies with Heterobasidion annosum on young trees of Picea abies

Infection studies with Heterobasidion annosum were carried out on 15-year-old, cloned spruces between 1971 and 1978. The inoculum was introduced into the sapwood of the test plants at the base of the stem. All inoculations, conducted at different times of the year, were uniformly successful. The pathogen spread through the xylem tissue rapidly during the vegetation period, but from early autumn onwards gradually disappeared over the following two years. After this period, the fungus could no longer be detected.     

Heterobasidion annosum infection of Picea abies following manual or mechanized stump treatment

Heterobasidion annosum (Fr.) Bref. s. l. colonization following thinning was studied in 1246 stumps of Picea abies (L.) Karst. trees from 14 previously unthinned stands in Sweden. Treatments included mechanized and manual application of (1) 35% urea solution, (2) Phlebiopsis gigantea (Fr.) Jül. spores, and (3) 5% solution of disodium octaborate tetrahydrate (DOT), and untreated stumps, cut in the summer and winter. Compared with untreated stumps cut in the summer, all stump treatments and winter cuttings significantly reduced the colonized stump area 6–7 weeks after thinning by 88–99%. Mechanized stump treatment provided as good protection as manual treatment against H. annosum infections. The probability of spore infection (p _ij ) was reduced by 53–83% in mechanized treatment and 79–98% in manual treatment compared with untreated summer thinning. In terms of p _ij , urea had significantly higher control efficacy than P. gigantea and manual treatment performed better than mechanized treatment.     

Variation in growth of Heterobasidion parviporum in a full-sib family of Picea abies

Abstract

Heterobasidion parviporum (Fr.) Niemelä & Korhonen and Heterobasidion annosum (Fr.) Bref. sensu lato are some of the major forest pathogens in the northern hemisphere causing root and butt rot to conifers. The relative susceptibility to H. parviporum was investigated in a full-sib family of Norway spruce [Picea abies (L.) Karst.] by inoculating a set of 252 cloned progenies from a controlled cross. Four ramets of each progeny were used and the 2-year-old rooted cuttings were incubated for 6 weeks under greenhouse conditions. The condition of the cuttings was assessed visually and all the plants were in excellent vigour with no mortality recorded during the experiment. To score the relative susceptibility, lesion length in the inner bark and fungal growth in the sapwood were measured. Among the progenies, significant differences were found for fungal growth in the sapwood (p<0.0005). There was no significant difference for lesion length; however, there was a significant positive correlation between fungal growth and lesion length. The broad-sense heritability was 0.11 for fungal growth. This shows that the genetic component for susceptibility to H. parviporum can be detected even within a full-sib family of Norway spruce and that there is a potential for mapping quantitative trait loci for this trait in Norway spruce.     

Infection of roots of Norway spruce (Picea abies) by Heterobasidion annosum

Wounding of excised roots of Norway spruce [Picea abies (L.) Karst.] caused a rapid accumulation of phenolic compounds, decrease of starch content and of certain enzyme activities in the ray cells. Infection of the wounds by Heterobasidion annosum (Fr.) Bref. intensified these processes, caused oxidation of the phenols, and induced activity of acid phosphatase and β-glucosidase in the ray cells of the infected area. The reactions were oxygen-dependent. Intra- and extracellular enzymes were detected in the wood-infecting hyphae. Other wood-growing fungi caused similar reactions in the wood as H. annosum.     

Transfer of the P-type of Heterobasidion annosum from old-growth stumps of Picea abies to Picea abies and Larix×eurolepis

The infection of Picea abies and Larix x eurolepis by Heterobasidion annosum was studied in felled trees in Sweden. Thinnings were carried out in two stands of L. x eurolepis, 15 and 20 years old, and in a 25-year-old stand of P. abies, established on a site heavily infected by H. annosum. The 15- and 20-year-old L. x eurolepis stands exhibited the greatest incidence of butt rot with infections amounting to 38 and 57%, respectively, of removed trees. The incidence of butt rot in the P. abies stand was only 5%. Heterobasidion annosum was the main butt rot causing fungus. All isolates of H. annosum were of the P-intersterility group. Transfer of H. annosum from old-growth P. abies stumps to trees felled in the thinning of the next generation was demonstrated by somatic incompatibility tests. However, the majority of infections could not be connected with decay already established in the previous generation. In L. c eurolepis, rot columns were frequent, including also several genotypes in the same stem, and typically positioned in the inner sapwood. The few infections of P. abies were situated in the heartwood.     

Resistance of Picea abies seedlings to infection by Heterobasidion annosum in relation to drought stress

Norway spruce (Picea abies) seedlings, 2–4 years old, were subjected to different degrees of stress. Drought stress affected the predisposition to infection by Heterobasidion annosum in the same way in root wood, stem wood and stem bark. At high water potentials (?3 to ?5 bar) resistance was high, at intermediate levels (- 5 to - 15 bar) it was low but increased again at water potentials below - 8 to - 15 bar. Neither light nor oxygen deficiencies appeared to have adverse effects on resistance. Total length of unsuberized roots was a sensitive indication of strain on the seedlings.     

Spore deposition of Heterobasidion annosum coll. in Picea abies stands of North Karelia,eastern Finland

Spore deposition of Heterobasidion annosum coll.was measured with the wood disc method in 20 Norway spruce stands in June, July and September 1999 in North Karelia, eastern Finland. The study area crossed the presently known northern boundary of the distribution area of H. annosum (62°45′N). The spore deposition rate decreased northwards and in the northernmost parts of the study area, deposition was detected only in September. On average 71% of the spore deposition consisted of intersterility group P and 29% of intersterility group S. The proportion of S‐type in the deposition increased northwards. Most of the isolated colonies were homokaryons, but the proportion of heterokaryons increased with increasing deposition rate.     

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 Butt-rotted Picea abies Stand Infected by Heterobasidion annosum from the Previous Rotation

There are no instructions on the management of stands of Norway spruce [ Picea abies (L.) Karst.] in which butt rot caused by Heterobasidion annosum coll. (Fr.) Bref. was not discovered until the time of first thinning. A stochastic simulation model describing the spread of butt rot in a stand of Norway spruce was used with a new submodel describing the butt rot of young trees. Non-linear stochastic optimization was used to determine the most profitable management schedule of a young Norway spruce stand with butt rot. If the initial level of butt rot was 5% or 10%, or the stand was thinned in summer with stump treatment, one thinning with a rotation of 55 yrs was optimal. Two winter thinnings with a rotation of 61 yrs was optimal in an initially healthy stand. Optimizations indicated that silvicultural measures that decrease the transfer of H. annosum to next generation at clear-cuttings could be economically fulfilled.     

Stilbenes and resin acids in relation to the penetration of Heterobasidion annosum through the bark of Picea abies

Concentrations of the stilbene glucosides astringin and isorhapontin, which ranged from 5 to 50 mg/g fresh weight in Picea abies bark, decreased in response to in vivo infection with the root-rot fungus Heterobasidion annosum. The initial concentration of the stilbene astringin was negatively correlated with the depth of hyphal penetration. Resin acid contents increased following infec-tion, but were not correlated with the depth of hyphal penetration. The spatial distribution of stilbene glucosides in spruce stem, root collar and root bark, and the seasonal variations in con-centration, were estimated.     

S and P intersterility groups in Heterobasidion annosum; Infection frequencies through bark of Picea abies and Pinus sylvestris seedlings and in vitro growth rates at different oxygen levels

Seedlings of Norway Spruce and Scots Pine were inoculated with S and P strains of the root rot fungus Heterobasidion annosum. Infection frequencies through the living bark layers were not related to subgroup affiliation in neither spruces nor pines. Growth rates in vitro were not related to growth rates in vivo. Oxygen concentration had a stronger effect on the growth rates of P than on S strains.     

Untersuchungen zur biologischen Bekämpfung von Heterobasidion annosum an Fichte (Picea abies) mit antagonistischen Pilzen

Investigations on biological control of Heterobasidion annosum in Norway spruce (Picea abies H. Karst.) with antagonistic fungi. I. Production of inoculum and interaction experiments in vitro. Thirty isolates of 22 fungal species were examined in vitro for sporulation, for germination of the spores, and for antagonism of mycelia against three strains of H. annosum. Viable spores were produced by 17 isolates, antagonism was shown by 28 isolates.     

Mycelial growth and exclusion of Heterobasidion parviporum inoculated in branches of 15‐year‐old Picea abies clones

Twigs of 22 clones of 15‐year‐old Picea abies grafts were inoculated with Heterobasidion parviporum in July and in September 2003. Fungal growth varied between clones and exclusion of the pathogen varied significantly among clones inoculated in July. The results indicate that twigs exhibit the same infection pattern as cuttings when inoculated with H. parviporum and that exclusion of the pathogen in twigs is a clone‐dependent character that occurs during the vegetation period.     

Antifungal properties of terpenoids in Picea abies against Heterobasidion parviporum

The antifungal properties of 14 major oleoresin‐constitutive terpenoids of Norway spruce (Picea abies) against Heterobasidion parviporum were evaluated in vitro at three gradient concentrations, 0.1, 0.2 and 0.4 μmol/cm², on potato dextrose agar medium. Eight monoterpene hydrocarbons (+)‐ and (?)‐α‐pinene, (?)‐β‐pinene, (+)‐3‐carene, myrcene, (+)‐ and (?)‐limonene, terpinolene; four oxygenated monoterpenes α‐terpineol, terpinen‐4‐ol, 1,8‐cineole, bornyl acetate; and two resin acids abietic acid and dehydroabietic acid were selected. Abietic and dehydroabietic acids showed the highest antifungal activities at all concentrations. Among oxygenated monoterpenes, bornyl acetate and α‐terpineol showed antifungal activity at the highest concentration. Among monoterpene hydrocarbons, (+)‐α‐pinene showed similar activity to terpinen‐4‐ol and 1,8‐cineole at the highest concentration; however, it was lower than α‐terpineol and bornyl acetate. Other monoterpene hydrocarbons inhibited mycelial growth by <10%. Re‐extraction of medium surfaces after the test period revealed that most α‐terpineol and terpinen‐4‐ol remained unchanged on the surface but monoterpene hydrocarbons completely disappeared. However, notable fungal transformed products were observed on surfaces applied with 1,8‐cineole and bornyl acetate. Thus, mycelial growth inhibition of monoterpenoids might be caused by complex functions such as biodegradation and/or detoxification by interaction between mycelium and compound. These results provide a basis for future studies considering the role of chemodiversity in the comprehensive chemical defence of P. abies.     

Effects of scarification and mulch on establishment and growth of six different clones of Picea abies

Abstract

The effects of mulch and scarification on the establishment and growth of six clones of Norway spruce [Picea abies (L.) Karst.] were examined in a study in southern Sweden. Mulch and scarification reduced the amount of competing vegetation and tended to improve soil moisture and soil temperature. Budbreak occurred earlier for cuttings planted in the scarification treatment in comparison with the control and mulching treatment. Scarification increased survival and the combination of scarification and mulch resulted in the best growth. Gas exchange and the number of new roots were higher in planting spots covered with mulch. Clonal differences regarding gas exchange and growth were significant. Clones with a poor height growth also had a low gas exchange and a small number of new roots. In contrast, the clone with the best height growth had high gas exchange and a large number of new roots. Clonal effects on growth were greater than site preparation effects.     

Variation in Heterobasidion annosum detected by Random Amplified Polymorphic DNAs

The production of Random Amplified Polymorphic DNAs (RAPDs) by Polymerase Chain Reaction (PCR) was used to detect variation in the isolates of Heterobasidion annosum with various geographical origins. Specific RAPD products were detected for each of the intersterility groups: the European S, F, P and the North American S group. There was considerably more polymorphism found among European S than P isolates. The analysis of RAPDs was shown to be a simple and a fast way to generate DNA markers specific to the previously established intersterility groups and thus useful for diagnostic purposes.