Penetration of Picea sitchensis root bark by Armillaria mellea, Armillaria ostoyae and Heterobasidion annosum

Abstract

Penetration of root bark tissues of Picea sitchensis by Armillaria ostoyae, Armillaria mellea and Heterobasidion annosum was examined in the absence of wounds, in super®cial wounds (rhytidome tissues removed to expose the secondary phloem) and in wounds to the depth of the vascular cambium (deep wounding). Both species of Armillaria penetrated bark without prior wounding, but neither species formed rhizomorphs in this treatment. Armillaria ostoyae penetrated to 39 cell layers in depth by 48 days after inoculation of unwounded bark, whereas A. mellea penetrated 25 cell layers in the same time. Armillaria mellea penetrated super®cial wounds signi®cantly more rapidly than did A. ostoyae. Both species produced rhizomorphs within wounded host tissues. Inoculation of deep wounds with Armillaria resulted in a greater depth of bark necrosis with A. mellea than with A. ostoyae. In the absence of wounding, H. annosum failed to penetrate root bark tissues, but in both super®cial and deep wounds hyphae penetrated beyond the ligno±suberized boundary zone (LSZ) by 12 days after inoculation. Where no inoculations were made, super®cial or deep wounding led within 25 days to the restoration of a structurally continuous LSZ, and by day 48 the wound periderm (WP) was fully differentiated. In inoculated wounds, however, formation of the LSZ and WP was delayed or inhibited in most trees, particularly following inoculation with A. ostoyae or A. mellea. Suberization in the LSZ and WP remained diffuse and discontinuous 48 days after inoculation. Moreover, the presence of WP did not prevent further penetration of the tissues by the pathogens. Variations between trees in the depth of pathogen penetration were noted, possibly indicating differing susceptibilities of individual host genotypes. The possible host factors involved in resistance to penetration of root bark tissues by Armillaria and Heterobasidion are discussed.

Temporal and Spatial Profiles of Chitinase Expression by Norway Spruce in Response to Bark Colonization by Heterobasidion annosum

“…Heterobasidion annosum is a major root and butt rot pathogen of conifers causing tremendous economic losses worldwide. Suberized bark tissues form a strong barrier to penetration by this pathogen (20,33). Bark wounds caused by wind, animals, insects, and timber extraction expose the trees to this pathogen, which is characterized by a high spore deposition rate and long spore viability in bark (27,32).…”

Development of Ash Dieback in South-Eastern Germany and the Increasing Occurrence of Secondary Pathogens

“…The fungus is often associated with forest decline events and is generally considered as a contributing factor ultimately responsible for tree death following some other predisposing stresses [20]. Symptoms of the disease can be found on collar rots and were firstly described in Lithuania and Denmark [18,21,36], where ash dieback was found earlier. Recently, also reports from south-western Germany describe the disease symptoms [19].…”

“…For the mature stand in Freising, DNA was isolated out of dead petioles. (8) Infected branches 10 3 +* Kitzingen (11) Infected branches 10 3 +* Landau (13) Infected branches 10 6 +* Ruhpolding (18) Infected branches 10 8 -Töging (23) Infected branches 10 4 +* Wertingen (24) Infected branches 10 6 +* Pole forests Coburg (2) Infected branches 3 1 + Forchheim (4) Infected branches 3 1 + Freising (7) Fruiting bodies 6 6 + Landau (12) Infected branches 3 1 + Nördlingen I (16) Infected branches 3 2 + Nördlingen II (17) Infected branches 3 1 + (10) Infected branches 3 0 -Landau (14) Infected branches 3 3 + Schweinfurt I (19) Infected branches 3 2 + Schweinfurt II (20) Infected branches 3 3 + Töging I (21) Infected branches 3 1 + Töging II (22) Infected branches The sampling in the mature forest in Kitzingen has to be repeated, because we could not detect the fungus out of the collected branches by PCR analysis. For all the other study sites, positive detections of the fungus were possible.…”

Defence response of Sitka spruce before and after inoculation with Heterobasidion annosum: 1H NMR fingerprinting of bark and sapwood metabolites

“…During the infection process, H. annosum grows from the inoculation point through the bark and cambium tissues, prior to more rapid extension in damaged sapwood [27,54]. During attack of the bark tissues, starch reserves are depleted, as shown by the reduction in starch granules present in host cells around the pathogen during growth [25]. The timing of these changes coincides with the alterations in host metabolism that lead to the development of the ligno-suberized boundary zone (LSZ) and the redifferentiation processes ultimately producing the wound periderm tissues [50].…”

“…Bark is considered the first line of defence affecting the secondarily thickened tissues of conifers: Several studies have documented changes in the anatomy and chemistry of bark [17][18][19][20][21][22][23][24][25][26], such as formation of traumatic resin ducts and of a greater number of parenchyma cells; increased production of lignin, suberin, resins, and phenolic compounds. Sapwood, in contrast, has received relatively little attention in this type of research, although it contains living cells which can take part in host defence after fungal challenge [19,27,28].…”