Secondary spread of Heterobasidion annosum in white fir root-disease centers

Abstract

Tree mortality caused by Heterobasidion annosum Fr. (Bref.) in white fir (Abies concolor (Gord. & Glend.) Lindl.) often appears in clusters; symptoms in the infected trees include sapwood and heartwood decay in tree boles and roots. Although the pathogen can spread from tree to tree through root contacts, it is often confined to the initially infected trees or stumps. We devised a field inoculation study to determine comparative virulence of fungal isolates, rates and modes of fungal colonization, preferential direction of fungal colonization, and effect of root size on fungal growth in white fir roots. Fifty trees were inoculated with eight H. annosum isolates, and sampled at 4 and 12 months. Heterobasidion annosum caused purple-brown staining and incipient wood decay within 4 months. Isolates from stumps were as virulent as isolates from trees. Fungal colonization was less in smaller than larger roots. Fungal colonization was greater in the proximal (towards the bole) than in the distal direction. Most fungal colonization in the distal direction occurred during the 4 months postinoculation, while colonization in the proximal direction occurred throughout the year.Résumé : La mortalité causée par Heterobasidion annosum Fr. (Bref.) chez le sapin argenté (Abies concolor (Gord. & Glend.) Lindl.) se entraîne souvent la formation de trouées. Chez les arbres infectés, les symptômes incluent la carie du bois d'aubier et du bois de coeur dans le tronc et les racines. Même si le champignon pathogène peut se propager d'un arbre à l'autre par les greffes de racines, il est souvent confiné aux arbres ou aux souches initialement infectés. Nous avons conçu une expérience d'inoculation au champ afin de déterminer la virulence relative d'isolats du champignon, le taux et le mode de colonisation du champignon, la direction préférentielle de la colonisation et l'effet de la dimension des racines sur la croissance du champignon sur le sapin argenté. Cinquante arbres furent inoculés avec huit isolats de H. annosum et échantillonnés après 4 et 12 mois. Heterobasidion annosum a causé une coloration brun-pourpre et un début de carie en dedans de 4 mois. Les isolats qui provenaient de souches étaient aussi virulents que ceux qui avaient été récoltés sur des arbres. La colonisation était plus faible dans les petites racines que dans les grosses. Elle était plus forte en direction du tronc que vers l'extérieur. La plus grande partie de la colonisation vers l'extérieur est survenue pendant les 4 mois qui ont suivi l'inoculation, tandis que la colonisation vers le tronc se poursuivait pendant toute l'année. [Traduit par la Rédaction]

Enlargement of canopy gaps associated with a fungal pathogen in Yosemite Valley, California

“…Roots extend in various directions from the original gap maker and each root constitutes a separate set of probabilities for growth of the pathogen; the fungus may or may not grow along individual roots far enough to infect adjacent trees, there may be no adjacent trees, or adjacent trees (e.g., oaks or white fir) may not be susceptible to infection by H. annosum. Studies have shown that H. annosum rarely moves distally through smalldiameter roots (<9 cm diameter) in Abies concolor (Garbelotto et al 1997). While this has not been demonstrated in pines and cedars, this may account for the limited spread of the fungus at a distance from the original gap maker in our study.…”

“…Population variation in pathogen virulence and host susceptibility are two obvious influences on the spread of the pathogen. However, these attributes are difficult to test with H. annosum in mature trees and in the few studies that have been conducted, great differences in virulence or susceptibility have not been noted (Garbelotto et al 1997;Delatour et al 1998). It is not clear whether living trees associated with the root-disease gaps have survived because of resistance to the pathogen or simply by escape (e.g., lack of root contacts).…”

Integrating mechanistic disturbance models and stand dynamics of Norway spruce

“…The fungus can spread from the infected stumps to adjacent stumps and living trees through root contact or root grafts (Garbelotto et al, 1997;Garbelotto and Gonthier, 2013). Once established in a stand, the fungus is capable of surviving for several tree generations as it is able to spread to the subsequent tree generation; young Norway spruce understorey and planted seedlings (Piri, 2003a;Piri and Korhonen, 2007;Piri and Valkonen, 2013).…”

Small-scale disturbances and stand dynamics in Inonotus tomentosus infected and uninfected old-growth and partial cut wet, sub-boreal forests in British Columbia.

“…However, applying partial cut silviculture systems to sites where root disease is present may cause the disease to spread faster, due to a hypothesized increase in inoculum volume that may occur in the roots and stumps of harvested trees. This is known to occur with other root diseases such as Armillaria ostoyae and Heterobasidion annosum (Koening 1969;Cruickshank et al 1997;Garbelotto et al 1997), but the effect of harvesting on inoculum volume for I. tomentosus is unknown. This result was not supported by Whitney (1993) who reported that partial cut forests of Picea glauca had a lower proportion of individuals infected with I. tomentosus than unthinned forests.…”