Forest Pathology最新文献

Pueraria montana (syn. P. lobata) is native to East Asia but has become an invasive species in North America and Europe, where it causes considerable ecological and economic disruption. Leaf blight symptoms have been observed on P. montana during the humid summer and early fall across multiple regions in Korea. Fungal isolates from symptomatic leaves were identified as belonging to the genus Marasmius through both morphological examination and molecular analysis. Artificial inoculation tests confirmed the pathogenicity of the isolates. This study is the first record of a Marasmius sp. causing leaf blight on P. montana in Korea. Also, we provided detailed documentation of disease symptoms and the morphological and molecular characteristics of the pathogen.

Some mycoviruses cause hypovirulence in fungi, but the effects often vary among different host strains. Heterobasidion partitiviruses 13-an1 and 15-pa1 (HetPV13-an1 and HetPV15-pa1) have been associated with strain-specific and variable hypovirulence of Heterobasidion annosum, but variation in phenotypic effects of HetPV15-pa1 or the coinfection of these viruses on different host strains has not been studied previously. In this investigation, the effects of single and double partitivirus infections were first studied using six Finnish H. annosum strains on malt agar plates (MEA). Secondly, the effects of single and double partitivirus infections on the growth rate of four H. annosum strains were tested outdoors using Scots pine billets as a natural substrate. Against our expectations, on MEA plates, the single or double partitivirus infections of HetPV13-an1 and HetPV15-pa1 did not have significant effects on three of the fungal strains studied and they slightly accelerated the growth rate of three host strains. In the billet experiment, the double partitivirus-infected strains were more often assorted to the fastest growing group than virus-free controls. Based on these results, HetPV13-an1 and HetPV15-pa1 do not debilitate the tested H. annosum strains on agar plates or dead wood but may even slightly increase the growth rate of the mycelium on artificial medium and in non-competitive growth conditions in dead pine wood.

Serpula himantioides is a widely distributed wood rot fungus that causes heart rot in various tree species. In Japan, heart rot due to S. himantioides occurs in Chamaecyparis pisifera; however, changes in the wood fungal community composition accompanying the progression of heart rot in living trees remain unclear. In this study, we clarified the changes in the fungal community composition of heartwood as heart rot progresses by performing an amplicon sequence analysis using DNA samples collected from living C. pisifera trees with heart rot caused by S. himantioides. Additionally, the mode of decay progression was characterised according to non-hierarchical clustering. The composition of S. himantioides sometimes reached extreme levels as heartwood decayed. This result is consistent with the findings of a previous study on heartwood decay in broad-leaved tree logs. However, there was no clear relationship between fungal diversity and the decrease in wood density, which was inconsistent with the results of a previous study on logs. Thus, this inconsistency may be influenced by the highly selective environment within heartwood. A clustering analysis grouped samples into four clusters, and the trophic modes and wood saprotroph decay types of indicator operational taxonomic units (OTUs), which characterised each cluster, changed during the decay process. The indicator OTUs and environmental variables for each cluster revealed that the four clusters corresponded to the pre-decay and incipient, intermediate and advanced decay stages. The study findings may be useful for further elucidating the decay of living trees infected by wood rot fungi.

Tree nurseries play a key role in the Canadian economy and reforestation efforts, producing over 600 million seedlings annually. Despite rigorous management practices, nurseries are not exempt from pathogen outbreaks, which can be devastating on many levels. In October 2022, the public forest nursery of St-Modeste (Canada) noted an unusually high mortality rate among their 2-year-old balsam fir (Abies balsamea ) seedlings. Phytophthora abietivora, recently identified as responsible for the Phytophthora root rot (PRR) in Christmas tree plantations, was suspected to be the causative agent of the outbreak. The objectives of this study were to identify the pathogen(s) responsible for the outbreak in the nursery and determine its pathogenicity and transmissibility to other seedlings. After the isolation of the pathogen and molecular detection, it was confirmed that the epidemic was caused by P. abietivora. The pathogen was not only found on healthy-looking balsam seedlings, but also on many other tree species grown in the nursery showing no above-ground PRR symptoms, such as spruce seedlings. The strain isolated in the nursery proved to be highly infectious to Fraser fir seedlings, and results were exacerbated by artificial flooding of seedlings. More worryingly, the disease could be transmitted to susceptible recipient seedlings from asymptomatic donor seedlings. The pathogen could be detected in soil and roots from both donor and recipient seedlings. Together, these findings indicate the first report of an outbreak of P. abietivora on balsam fir seedlings under nursery conditions. Efforts must be increased to minimise economic losses and to manage future outbreaks better in order to protect Christmas trees and forests.

Aesculus is a genus of woody plant species that contains multiple ecologically and ornamentally important species. Powdery mildew is common on this host genus and is particularly virulent on the economically significant horse chestnut, Aesculus hippocastanum. Previously, all Erysiphe species found on Aesculus spp. were identified as Erysiphe flexuosa. Recent genomic research has indicated that powdery mildew species frequently show a high degree of host specificity which was not captured by traditional morphological approaches. As such, we proceeded to collect and sequence multiple regions of the powdery mildew genome to determine the causal agents of disease on different Aesculus spp. The results of our multilocus phylogenetic analyses revealed the existence of a genetically distinct species, which has been found only on Aesculus spp. native to North America. Erysiphe aesculi-sylvaticae sp. nov. is proposed for this cryptic species. In the past 25 years, there have been multiple reports of an E. flexuosa epidemic on Aesculus hippocastanum in Europe, while E. aesculi-sylvaticae has yet to be identified outside of the United States. The discovery of this new cryptic powdery mildew species as well as analysis of additional sequences from collections of E. flexuosa from North America, including from the type specimen collected in 1872, are discussed in detail with an emphasis on the implications for the co-evolution, worldwide spread, and invasion dynamics of these powdery mildews. Future research should continue to collect and sequence powdery mildews on different Aesculus spp. to better understand the diversity and spread of these economically important pathogens.