Forest Pathology最新文献

A novel fungal pathogen, Rhytisma arcticum, is described, causing tar spot disease on Salix arctica in Ellesmere Island, Canada. Stromata, asci and ascospores—distinctly smaller than other Rhytisma species found on Salix—are its distinctive morphological features. rDNA internal transcribed spacer (ITS) and large-subunit (LSU) sequence analyses revealed a close relation of this species to R. polare previously reported on Spitsbergen Island. This study describes a novel plant pathogen species in one of the northernmost locations of the world.

In declining broadleaf forests in western Ukraine, several Phytophthora species including P. plurivora, P. bilorbang, P. polonica, P. gonapodyides and P. cactorum were recovered using soil baiting assays and identified using morphological and molecular methods. Pathogenicity tests of selected isolates were performed on black alder (Alnus glutinosa (L.) Gaerth.) and silver birch (Betula pendula Roth.) to assess susceptibility of these two tree species to the newly detected Phytophthora species. Phytophthora plurivora, P. bilorbang and P. polonica showed higher pathogenicity in both alder and birch compared to the other tested Phytophthora species.

In October 2022, Erysiphe powdery mildew from the section Typhulochaeta was found on Quercus aliena for the first time in Korea. Based on morphological characteristics and molecular-phylogenetic analysis of the internal transcribed spacer region (ITS) and large subunit (LSU) gene sequences of the rDNA, the fungus was identified as Erysiphe japonica var. japonica. This is the first report of E. japonica var. japonica in Korea and the third report of this mildew on Q. aliena, with this current fungus-host association spreading to China and Japan. Based on Korean samples, this study provides detailed morphology and molecular phylogeny of E. japonica var. japonica.

The invasive fungal pathogen Cronartium ribicola causes white pine blister rust which is considered one of the most destructive diseases of five-needle (white) pines in North America. The disease has a life cycle that requires two hosts: white pines and Ribes spp., although other non-Ribes species, including Castilleja and Pedicularis, have been demonstrated as alternate hosts as well. Detection of this disease can be difficult because of the ephemeral nature of sporulation on pine hosts with ambiguity in other symptoms, and the alternate hosts for C. ribicola can also be an alternate host for other pine rust species. We used the previously published C. ribicola genome and species-specific real-time PCR assay to develop a field-ready loop-mediated isothermal amplification (LAMP) specific colorimetric assay for this pathogen. Specificity results across regionally identified pine rust pathogens showed the assay is highly specific to C. ribicola and can detect as little as 40 pg of pathogen DNA. We also developed a simple DNA extraction method that works with several tissue types (bark/phloem, aeciospores, and urediniospores/telia) to prepare the DNA samples for the LAMP assay. The DNA extraction and LAMP assay take ~70 min to complete and require a relatively small investment in equipment. This tool enables quick and efficient detection of white pine blister rust.

The Agaricomycete Heterobasidion annosum sensu lato (s.l.), a species complex of fungal pathogens, causes root and butt rot on conifers throughout the northern hemisphere, thereby shaping structure, composition, and evolution of vast and diverse forest ecosystems. We analyze forest change 48–49 years following Heterobasidion root disease emergence in 63 permanent plots first established in 1970–1972 and measured at least once every decade through 2020. We use this dataset to infer the long-term consequences of Heterobasidion root disease in a set of common forest types that reflect some of the most important hosts for this set of diseases in western North America. We contrasted three host–pathogen systems located within the Sierra Nevada, southern Cascades Mountain Range and the Modoc Plateau: (1) H. irregulare in host communities dominated by several Pinus (pine) species and Calocedrus decurrens (incense cedar) in Yosemite Valley, on the Sierra Nevada Range western slope; (2) H. irregulare in a largely single species (Pinus jeffreyi) host disease system on the eastern slopes of the Sierra Nevada and southern Cascades as well as the Modoc Plateau; and (3) H. occidentale—also on the western slope of the Sierra Nevada—in stands with a mixture of susceptible Abies (true fir) and a diversity of non-hosts for this Heterobasidion species. Approximately 50 years after disease emergence, relative basal area and stem density were significantly reduced within disease centres in all three pathosystems, but changes to forest composition and relative species dominance were determined by pre-disease host and non-host diversity. In the western-slope H. occidentale system, the disease increased the dominance of non-susceptible species, Pinus species and C. decurrens. In the multi-genus Yosemite pathosystem, H. irregulare did not significantly shift species dominance, and as expected, species shifts did not occur in the largely single-genus eastern-slope forests. In these widespread California forest ecosystems, two factors appeared to determine forest conditions almost 50 years after Heterobasidion root disease monitoring: the size of the disease centre and the initial diversity of non-hosts. Along with pathogen species, these factors appear to affect the local severity of disease as well as the degree of species shifts relative to initial plot compositions, reaffirming host susceptibility classifications associated with these forest types.

Styphnolobium japonicum (L.) Schott is a deciduous tree belonging to family Fabaceae and has been widely planted as garden greenery in China. In May 2021, a serious branch canker disease was observed in Alaer City. In order to identify the pathogen, five fungi were isolated from the diseased branches and the pathogenicity was evaluated by inoculating the branches outdoors. The pathogen was re-isolated from all the inoculated branches, therefore fulfilling Koch's postulates. Based on the morphological characteristic and polygenetic analysis using the internal transcribed spacer region, β-tubulin and the translation elongation factor 1-alpha, the pathogen was identified as Fusarium solani. This is the first report of F. solani as the causal agent of a branch canker of S. japonicum in Xinjiang of China.

The detection of stem water content is necessary as it is an important indicator for measuring woody plant vitality. However, the relationship between stem water content, determined by non-destructive, real-time, and long-term monitoring, and woody plant vitality remains undefined. In this study, the response of woody plant vitality to stem water content under different stress (freeze–thaw, pest, or drought) was analysed by mining the dynamic characteristics of the stem water content in different woody plants at the temporal scales of year, month, and day. Compared with unstressed trees, stressed trees had contrasting diurnal patterns. The stem water content in Populus koreana Rehd. during the freeze period was much lower than that during the thaw period, and opposite diurnal variation trends were observed during the freeze and thaw periods. The stem water content in infected Lagerstroemia indica was lower than that in uninfected L. indica, and the amplitude of the diurnal variation curve was lower in infected than in uninfected L. indica. Under drought stress, the more severe the water shortage, the lower the stem water content in Malus micromalus. When it was below a certain threshold, the diurnal variation trend was opposite to that without water shortage. In conclusion, stem water content dynamics can be used to evaluate the cold, pest, and drought response of trees, which could monitor tree health and guide forest assessment.

Vegetative compatibility (vc) and mating types and genetic diversity of Cryphonectria parasitica isolates were determined using 183 isolates obtained from 215 infected chestnut trees growing in 13 provinces of Turkey. Based on the cultural aspects, 143 of these isolates were evaluated as virulent whereas the remaining 40 isolates were hypovirulent. When vc types of 183 isolates were classically differentiated, 135 of them matched to EU-1 (82.3%), 29 of them to EU-12 (17.6%) vc type, whereas 19 of them did not match to the two. When molecular vic markers were used, all the isolates were assigned to two EU vc types; 149 to EU-1 (81.4%) and 34 (18.5%) to EU-12. Of the majority of the isolates, 134 (73.2%) had mating-type MAT-1, while 44 (24%) isolates had MAT-2 and 5 (2.8%) isolates had both mating types. The population analysis based on two DNA marker systems, Inter-Primer Binding Site and Start Codon Targeted Polymorphism, showed no intraspecific genetic variation among the C. parasitica isolates. The prevalence of two dominant vc types revealed by this study shows that biological control with hypovirulent EU-1 and EU-12 isolates will be significant for the country. The results might be helpful to chestnut breeders carrying out resistance breeding studies to manage this disease based on hypovirulence attributed to Cryphonectria hypovirus 1.

The ecologically and culturally vital tree species, ʻōhiʻa lehua (Metrosideros polymorpha), is threatened by the fungal pathogens Ceratocystis lukuohia and Ceratocystis huliohia, the causal agents of the disease complex called Rapid ʻŌhiʻa Death (ROD). Four invasive ambrosia beetle (Coleoptera: Curculionidae: Scolytinae) species in the Xyleborini tribe colonize ROD Ceratocystis-infested ‘ōhiʻa and produce inoculum through their frass; however, the potential for direct transmission of the ROD fungi by these beetles was unknown. We fulfilled Leach's rules to support insect transmission of ROD by documenting the visitation of these ambrosia beetles to healthy ‘ōhiʻa trees, culturing C. lukuohia and C. huliohia from the ROD-associated beetles using three different collection methods at multiple study sites, and challenging healthy ʻōhiʻa seedlings with beetles that were exposed to both C. lukuohia and C. huliohia cultures. We documented all four invasive ROD-associated ambrosia beetle species including Xyleborinus saxesenii, Xyleborus affinis, Xyleborus ferrugineus, and Xyleborus perforans to regularly visit healthy ʻōhiʻa trees on sticky traps. Viable Ceratocystis propagules were isolated from all species, and C. lukuohia was most commonly isolated of the two ROD-causing fungi. Consistently across all collection techniques, ROD Ceratocystis spp. were detected on just under 3% of all assayed beetles, with the highest detection rate from X. affinis. All four beetle species were capable of directly transmitting both pathogens to healthy ʻōhiʻa seedlings with a high rate of transfer. Ceratocystis spp. are highly virulent pathogens in trees, and a single inoculation can result in tree death, therefore any direct transmission is a cause for concern. After meeting the criteria of Leach's rules, we propose that Xi. saxesenii, X. affinis, X. ferrugineus, and X. perforans are vectors of C. lukuohia and C. huliohia, particularly in areas of high ROD pressure and tree stress.

Our knowledge of the endophytic fungal community associated with needles of Sitka spruce (Picea sitchensis) is rather limited, which contrasts with the importance of this tree species for forestry in the UK. In our study, we focused on the detailed characterization of multiple isolates tentatively placed into the genera Nothophaeocryptopus and Rhizosphaera that were obtained from needles of Sitka spruce and co-occurring Norway spruce (Picea abies) and Douglas fir (Pseudotsuga menziesii) at four sites in Scotland and Wales. After a thorough analysis of their phenotype and analysis of two nuclear regions (ITS rDNA and gene for β-tubulin), we propose two species new to science and one new combination. Nothophaeocryptopus piceae was isolated from healthy green or brown needles from spruces and is currently known only as a sterile culture, but the taxonomic novelty is well supported by host affinity and results of molecular data analysis. Rhizosphaera minteri may also be distinguished based on the combination of host and molecular data, but morphologically, it is similar to R. pini. Finally, Hormonema merioides and R. pseudotsugae are found to be conspecific and a new combination R. merioides is proposed following the phylogenetic placement of this species. Our study highlights the importance of multiple approaches used in the identification of microfungi associated with coniferous needles. It is evident that morphologically identical fungi may represent distinct species differing in their host range and severity on the host. This study also provides a basis for future monitoring of these fungi associated with important coniferous forestry trees in the UK.