Spatial Patterns in Hyphal Growth and Substrate Exploitation within Norway Spruce Stems Colonized by the Pathogenic White-Rot Fungus Heterobasidion parviporum

Abstract

In Norway spruce, a fungistatic reaction zone with a high pH and enrichment of phenolics is formed in the sapwood facing heartwood colonized by the white-rot fungus Heterobasidion parviporum. Fungal penetration of the reaction zone eventually results in expansion of this xylem defense. To obtain information about mechanisms operating upon heartwood and reaction zone colonization by the pathogen, hyphal growth and wood degradation were investigated using real-time PCR, microscopy, and comparative wood density analysis of naturally colonized trees with extensive stem decay. The hyphae associated with delignified wood at stump level were devoid of any extracellular matrix, whereas incipient decay at the top of decay columns was characterized by a carbohydrate-rich hyphal sheath attaching hyphae to tracheid walls. The amount of pathogen DNA peaked in aniline wood, a narrow darkened tissue at the colony border apparently representing a compromised region of the reaction zone. Vigorous production of pathogen conidiophores occurred in this region. Colonization of aniline wood was characterized by hyphal growth within polyphenolic lumen deposits in tracheids and rays, and the hyphae were fully encased in a carbohydrate-rich extracellular matrix. Together, these data indicate that the interaction of the fungus with the reaction zone involves a local concentration of fungal biomass that forms an efficient translocation channel for nutrients. Finally, the enhanced production of the hyphal sheath may be instrumental in lateral expansion of the decay column beyond the reaction zone boundary.

Genes associated with lignin degradation in the polyphagous white-rot pathogen Heterobasidion irregulare show substrate-specific regulation

“…complex is manifested by an ability to challenge active bark defenses and the unique secondary xylem defense tissue [reaction zone wood (RZ)] characterized by polyphenols that have been actively deposited in tracheid and ray cell lumens by the living sapwood cells (e.g. Hietala et al, 2009). Furthermore, the tracheid cell wall lignin is a feeding obstacle that H. annosum s.l.…”

“…For the two Eurasian species H. annosum sensu stricto and Heterobasidion parviporum (Niemelä and Korhonen, 1998), both selective and non-selective wood lignin decay modes have been reported (Daniel et al, 1998). Besides the ability to kill vascular cambium and the living cells of inner bark upon fungal penetration through roots, in conifer trees such as Norway spruce (Picea abies), Heterobasidion species can tolerate and presumably detoxify the polyphenols that accumulate as a tree defense response [reaction zone wood (RZ)] opposing the expanding fungal decay columns in the root and stem xylem (Hietala et al, 2009). …”

Carbon Dioxide and Methane Formation in Norway Spruce Stems Infected by White-Rot Fungi

“…The flux based estimates are from the five Heterobasidion infected trees monitored at Hokksund and the one monitored at Ås. Wood density estimates are based on stem section data of one Norway spruce tree that showed an extensive stem decay column caused by Heterobasidion parviporum in our previous study [26] (tree #9).…”

“…To test how the estimated fluxes conformed to biomass loss from rotten wood, we used the wood density profiles measured from a Norway spruce tree with an advanced stem decay column caused by Heterobasidion parviporum [26]. The estimated biomass loss was converted to annual CO2 flux in kg per square meter by converting the distance between the sampling points to colonization time with the assumption of a constant vertical spread of decay.…”

Heterobasidion annosum s.l. and wood degradation of Norway spruce (Picea abies): the effects of sectioning, crown type and wood properties

“…is regarded as one of the most serious and important forest pathogen that causes butt and root rot, especially in boreal forests (Hietala et al 2009). This basidiomycete (Russulales, Bondarzewiaceae) represents the first "sequenced plant pathogenic homosidiomycete" bearing a complete genome sequence (Olson et al 2012;Garbelotto and Gonthier 2013 (Dalman et al 2010), and three in Europe (Niemelä and Korhonen 1998 Niemelä & Korhonen (F type).…”