Forest Pathology最新文献

Heterobasidion parviporum is a fungal pathogen that is drastically damaging Norway spruce (Picea abies) in Europe. The infections will result in root and stem rot, causing significant economic losses for forest owners. Previous studies have shown that the PaLAR3 gene, which encodes the leucoanthocyanidin reductase enzyme, can increase resistance to H. parviporum in Norway spruce. The presence of the B allele at the PaLAR3 locus has been associated with higher (+)-catechin concentrations and increased enzyme production in inoculation experiments, resulting in inhibited pathogen growth. The control of H. parviporum involves a multifaceted approach, including silvicultural and sustainable forestry practices, genetic resistance and chemical/biological control. In this study, we determined the PaLAR3 genotypes in a representative sample of Norway spruce breeding materials from southern Finland and examined their effect on necrosis caused by H. parviporum in spruce stems. The results showed that the homozygous PaLAR3BB genotype was present in only 9% of the trees. However, the necrotic area interacted with homozygous PaLAR3BB under low-water treatment. These findings support the idea that the PaLAR3 locus may be a valuable marker for identifying P. abies resistance to different strains of Heterobasidion parviporum.

Recent studies have shown numerous Fusarium spp. are associated with symptomatic conifer seedlings in both bareroot and container nursery systems. Some of these species have been found pathogenic to conifer seedlings (e.g., F. avenaceum, F. commune, F. oxysporum, F. solani, and F. verticillioides), but the mechanisms and shared evolutionary history of these conifer pathogenic species have not been well studied in these pathosystems. We compared whole genomes of 17 Fusarium spp. associated with conifer seedlings to elucidate putative shared pathogenicity/virulence gene profiles presumably expressed for roles in causing damping-off and/or root disease of conifer seedlings. In addition, this work provides draft genomes of conifer-associated Fusarium spp. and genomes not previously referenced in public databases (e.g., F. lactis, F. fredkrugeri, F. ipomoeae, and F. flocciferum). We identified pathogenicity/virulence genes associated with Fusarium spp. pathogens of conifers including effectors, the secreted in xylem (SIX) genes 2, 4, 9 and 14 and secondary metabolites, and the mycotoxins fumonisin and deoxynivalenol. We conclude that gene profiles are shared within Fusarium species complexes and among closely related Fusarium species complexes; however, these shared profiles are widely distributed across all Fusarium pathogens. These findings highlight potential targets for detecting and/or identifying Fusarium pathogens of conifers, but multiple methods and/or targets will be required depending on the species complexes and clades. More research is needed to determine the roles of expressed pathogenicity/virulence genes and the downstream metabolic products that result in pathogenesis to conifers.

A real-time PCR TaqMan assay was developed for the detection of Calonectria canadiana, a fungal pathogen responsible for damping off, root rot and seedling blight in conifer forest nurseries in central and eastern North America. While highly significant in Quebec Forest nurseries, coniferous seedling mortality decreased significantly when nurseries transitioned from bare root to container seedling production. However, over the past few years, this pathogen has re-emerged as a threat and millions of container white spruce seedlings were culled in two nurseries in eastern Quebec. A sensitive detection and quantification assay for C. canadiana was essential to investigate the biological and environmental factors driving this new epidemic. We designed primers and a TaqMan probe targeting the internal transcribed spacer (ITS) of C. canadiana. The resulting Ccan TaqMan assay successfully differentiated C. canadiana from other soil-borne pathogens of the Nectriaceae encountered in Quebec Forest nurseries. The limit of detection of the assay was established at eight copies of C. canadiana ITS. The Ccan TaqMan assay quickly identified the presence of the pathogen in both symptomatic and asymptomatic white spruce (Picea glauca) seedlings. Furthermore, we demonstrated that the pathogen was more easily detected when DNA was extracted from necrotic needles at the base of the stem rather than from necrotic roots. This molecular tool will greatly aid in understanding the biology and epidemiology of C. canadiana.

Botryosphaeriaceae fungi cause infections that generate disease symptoms in plants in extreme environments. The present study identified the causal agent of dieback disease on lebbeck trees in Saudi Arabia. Albizia lebbeck trees showed widespread dieback, decline and cracking symptoms of samples taken during a Qassim University, Saudi Arabia survey. The survey showed that over 80% of lebbeck trees showed wilted roots, stem cankers and death of wilted trees. Fungal colonies were obtained from symptomatic tissues cultured on water agar for 3 weeks at 25°C. Elongation factor alpha (EF1-728 F, AL33R), ITS (ITS4) and LSU (128) regions of the rDNA operon and the partial beta-tubulin gene (tub2; Bt2aF, Bt2bR) were sequenced for molecular identification. Based on morphological and molecular characterization, the pathogen was identified as Neoscytalidium dimidiatum. During the pathogenicity investigation, the fungus re-isolated from the infected seedlings expressed the same morphological characteristics on the culture media as the N. dimidiatum isolate. A host range study involving six tree species inoculation with N. dimidiatum caused wilting and death in three plants. To our knowledge, this study is the first to report on N. dimidiatum in Saudi Arabia.

In Europe, Pinus sylvestris and Picea abies are the most common coniferous tree species used in commercial forestry, which rely on high-quality reproductive material for successful reforestation. Clear-cut harvested forest sites are often replanted using tree seedlings, which are produced in forest nurseries using seeds from seed orchards. However, incidences of fungal diseases in seedling production show that a better knowledge of seedborne fungi, including fungal pathogens, is needed to manage diseases in forest nurseries. This study aimed to assess seedborne fungal communities associated with commercial seeds of P. abies, P. sylvestris and Larix sp. seeds originated from geographically separated regions in Sweden, Belarus, Finland and Poland. Fungal communities were obtained first from the seed surface and then from the seed tissue. These were analysed using high-throughput sequencing of the ITS2 rDNA region. The results showed that fungal diversity and community composition differed between the seed surface and the seed tissue. Picea abies accommodated a higher fungal diversity than P. sylvestris. In addition, a strong host affinity of the fungal community composition on the seed surface and a weaker association in the seed tissue was found. Fungal communities on P. abies and P. sylvestris seed surface differed significantly between geographical regions, whereas no regional differences were found in the seed tissue. The seedborne fungal communities included a high proportion of plant pathogens, among which the most abundant were Sydowia polyspora (13.3%), Phoma herbarum (11.2%) and Sirococcus conigenus (3.8%). In conclusion, the results showed (a) characteristic fungal diversity and community composition between the seed surface and the seed tissue; (b) a host-specific fungal community composition on the seed surface and in the seed tissue; (c) regional difference in fungal communities on P. abies and P. sylvestris seed surface, thus the movement of seeds between different regions can contribute to the spread of fungal diseases; and (d) the presence of a high incidence of seedborne fungal pathogens which suggest a potential need of preventative or control measures to reduce the occurrence of these fungi on the seed surface.

Areca ipot, a Philippine endemic species, is categorized as endangered primarily due to habitat loss. A severe outbreak of a new leaf spot disease was observed on A. ipot seedlings in a nursery. Morphological and molecular features of isolates from diseased samples were identified as Neopestalotiopsis sp. and Calonectria sp. The pathogenicity of the isolates was confirmed by fulfilling Koch's postulates. This is the first report of Neopestalotiopsis sp. and Calonectria sp. causing leaf spot on A. ipot in the Philippines.

When monitoring the health status of various woody host plants in urban areas in Serbia, symptoms indicative of Cryphonectria-like infection were recorded on European hornbeam (Carpinus betulus) trees in the natural monument ‘Arboretum of the Faculty of Forestry in Belgrade’. One tree was affected by crown dieback while another one showed dieback of branches. Bark lesions were found on stems which contained numerous stromata with fruiting bodies and orange tendrils. Conidiomata were recorded solely in the infected tissue, producing hyaline, aseptate and bacilloid-shaped conidia with dimensions of 3.4 ± 0.46 × 1.2 ± 0.12 μm. In the isolation tests, all plated bark pieces were positive, and 25 isolates were obtained. Colonies on different agar media were white in the beginning, turning into orange-red colour during ageing. Optimum temperature for growth was 25°C and no growth was recorded at 30°C. A GenBank blast search and a phylogenetic analysis of ITS rDNA sequences of five representative isolates revealed their identity as Cryphonectria carpinicola. To our knowledge, this is the first report of C. carpinicola on hornbeam trees in Serbia, and implications of this finding are discussed.