Forest Pathology最新文献

Bacterial wilt (caused by Ralstonia spp.) is one of the most damaging diseases of Eucalyptus species, and is responsible for substantial losses to producers. For efficient, scientifically-based management of this disease, it is necessary to understand the various factors involved in its development, including greater knowledge of the epidemiology of the pathogen on Eucalyptus spp. This study aimed to determine the spatialtemporal dynamics of bacterial wilt in Eucalyptus under natural infection conditions. An experiment was conducted in a commercial plantation in the municipality of Itinga, state of Maranhão, Brazil, using the clone FGCA0385 (Eucalyptus urophylla var. platyphylla). The study comprised of four plots composed of 450 plants each, subdivided into nine rows with 50 plants per row with a spacing of 3 × 3 m. Disease incidence was quantified over 1 year. The spatial dynamics of the disease was determined using the dispersion index, a modified Taylor law, and the analysis of the dynamics and structure of foci. For temporal dynamics, the curve of the disease incidence progress was plotted, and the data were analysed by simple linear regression analysis fitted to three empirical models: logistic, monomolecular, and Gompertz. The distribution pattern of Eucalyptus bacterial wilt was random, as confirmed by the Index of dispersion. Analysis of the dynamics and structure of the foci, showed that 69 disease foci occurred, 44 of which were unitary, with an average number of plants per focus of 1.63. Foci had greater length in the direction of the planting line. The epidemics were best described by the monomolecular model, with an estimated incidence of Eucalyptus bacterial wilt of 27.77% in the fourth year of the study. According to the spatiotemporal dynamics of this work, management strategies such as eliminating symptomatic plants and crop renovation can be used based on economic viability.

In December 2020, Euphorbia leucocephala plants exhibiting symptoms of powdery mildew were observed in the Botanical Garden of Tuljaram Chaturchand College, Baramati, Maharashtra, India. Based on morphological identification, DNA sequence analysis, and pathogenicity, the fungal pathogen of the disease was identified as Leveillula clavata. This is the first report of L. clavata on Euphorbia leucocephala from India and in general.

Thuja occidentalis is a popular and widely planted tree in Russia. However, it is susceptible to arborvitae foliar blight, which can compromise the long-term health of trees in the landscape and in nursery production. Leaves with arborvitae needle blight were collected in 2019 in the foothill zone of the Republic of Adygea, and two isolates of Phyllosticta sp. were obtained. Multilocus analyses were performed with sequences of the internal transcribed spacer and 28 S rDNA of the ribosomal DNA, partial actin gene, partial RNA-polymerase II gene, and partial translation elongation factor 1-alpha. Based on phylogenetic analyses combined with morphological features the isolates were identified as Phyllosticta spinarum. Following inoculation of the original host species both isolates produced symptoms similar to those observed in naturally infected leaves. Koch's postulates were then fulfilled by re-isolating P. spinarum from the inoculated leaves. These findings represent the first confirmed detection of P. spinarum causing arborvitae needle blight in Russia.

Beetles (Scolytinae) form intimate associations with a taxonomically and functionally diverse suite of nematodes that are phytopathogens, fungal feeders, and entomoparasites. Despite their ubiquity, the ecological significance of nematodes in the lifecycles of economically important bark and ambrosia beetle species (Curculionidae: Scolytinae) and associated plant diseases remains largely unexplored. Thousand cankers disease (TCD) is caused by the walnut twig beetle (WTB, Pityophthorus juglandis Blackman) and the fungus Geosmithia morbida (Kolařík, Freeland, Utley & Tisserat; Ascoymycota: Hypocreales) and causes foliar senescence, progressive crown dieback, and mortality in black walnut (Juglans nigra L.) throughout western North America. In this study, nematodes recovered from P. juglandis and J. nigra in Idaho (ID) and Washington (WA) were identified morphologically and by constructing multilocus phylogenies to infer taxonomic relationships to taxa for which molecular data were available. We conducted assays to determine the extent to which nematodes feed and reproduce on G. morbida and other fungi commonly found in galleries of P. juglandis. Inoculation experiments were conducted to determine the effect of nematodes on the area of subdermal necrotic lesions (cankers) caused by G. morbida in branches of mature J. nigra and stems of seedlings. The phoretic nematode Bursaphlenhus juglandis (Ryss, Parker, Alvarez-Ortega, Nadeler & Subbotin) was frequently found under elytra of WTB in all locations, and a free-living nematode (Panagrolaimus sp.) was also widespread and found in the bark of mature trees. Both B. juglandis and Panagrolaimus sp. reduced the size of cankers caused by G. morbida in seedlings and branches of mature trees, respectively. However, these species may play opposite roles as disease synergists and antagonists based on the observation that exudates and/or microbiota associated with Panagrolaimus sp., but not B. juglandis destroyed G. morbida colonies in culture. Furthermore, B. juglandis contributed to foliar symptoms in seedlings inoculated with G. morbida. An entomoparasitic nematode (Aphelenchoididae), most closely resembling an Ektaphelenchus sp., was also found in the haemocoel of WTB. Infection rates were positively related to beetle population sizes as inferred from emergence rates. Ditylenchus sp. was also found in incubated walnut wood in WA and Rhabtidolaimus sp. was phoretic on P. juglandis and found in incubated walnut wood in WA and ID. The community of nematodes in J. nigra in WA and ID differed substantially from what has been observed associated with J. nigra in its native range.

Rigidoporus microporus is an economically important plant pathogenic fungus causing particularly severe losses to the rubber industry worldwide. The pathogen is responsible for white root rot (WRR) disease, infecting the host roots via white fibrous mycelia, causing vascular disfunction, and visible symptoms including leaf discolouration and dieback in severely infected trees. The final stage of the disease is characterized by the appearance of basidiocarps at the tree collar. The development of WRR in rubber plantations is dependent on fungal diversity in the soil, pH, temperature, and cation levels. Several ‘-omics’ approaches have been undertaken to understand how R. microporus functions with the objective, ultimately, to control WRR. Unfortunately, no resistant rubber clone has been identified to date. The disease is managed through physical and chemical methods that are laborious and negatively impact the environment, respectively. Recent developments in research on R. microporus shed light on potential sustainable routes to WRR disease control using beneficial microorganisms and natural compounds. This review discusses the characteristics of R. microporus isolates from different geographical origins, the pathogenicity and virulence mechanisms of the necrotrophic fungal pathogen, factors that influence the development of WRR, recent findings from the multi-omics studies, and control methods that are available to combat this economically important pathogen.

The introduction of Cronartium ribicola, the causative agent of white pine blister rust, has been devastating for white pines in North America, including western white pine. Among the observed partial resistance responses to white pine blister rust is a mechanism referred to as difficult-to-infect (DI), which is characterized by lower frequency of infection spots on needles and a lower incidence of branch and stem cankers than susceptible host plants. Parents with the DI trait were selected and bred to produce nine full-sib families. Progeny were propagated and cloned using in vitro techniques in controlled environmental conditions. Explants were inoculated with a single strain of C. ribicola and characterized by using a disease assessment index (DAI), which was used to compare DI full-sib families to several other full-sib families (from Idaho) selected for other partial resistance traits. Most DI families had significantly lower DAI scores and higher epicuticular wax content. When the wax was removed from the surface of needles, the DAI of all full-sib families increased. Scanning electron microscopy revealed that stomata in DI full-sib families are mostly occluded by epicuticular wax. The results of this study suggest that the DI resistance mechanism of western white pine is related to needle surface epicuticular wax, which likely hinders the penetration of stomata by fungal hyphae. The occurrence and magnitude of this trait in the breeding population remains unknown, and special assessment technique for large-scale screening will have to be developed.

Christ's thorn (Paliurus spina-christi Mill.) tree is an important and valuable forestry species and has significant potential in afforestation and reforestation systems. In recent years, dieback symptoms were observed on Paliurus spina-christi trees in Gilan-e Gharb region of Kermanshah province, west Iran. During 2020 to 2021, Christ's thorn trees that exhibit branch dieback symptoms were sampled for fungal isolations. The pathogenicity tests, biochemical assay of growth, acid production on creatine sucrose agar (CREA) medium and morphological and molecular investigations (ITS and β-tubulin regions) identified Paecilomyces formosus as a dieback causal agent. This is the first report of P. formosus pathogenicity on Paliurus spina-christi trees. Furthermore, disease severity was assayed on 11 tree species under three different temperatures 15, 25 and 35°C. Disease severity caused by all isolates on detached branches was greater at 35°C than at 15 and 25°C. This study presents the host range of this pathogen and showed that these potential hosts are prone to this pathogen under high temperatures, which forest trees experienced in recent decades.

The study was carried out to identify wood-decay fungi, and quantify the diversity and host preferences of the fungi in major sawmill depots in north-eastern Bangladesh. A total of 23 fungal species belonging to 15 genera in seven families were recorded and identified. The Polyporaceae was the most dominant family, while Schizophyllum commune was the most abundant species among all species recorded. Other commonly observed fungal species were Daldinia concentrica, Trametes versicolor, Trametes coccinea and Flavodon flavus. The Simpson diversity index (0.93) and Shannon–Wiener index (2.90) showed a wide distribution of the wood-decay fungi in the study areas. The species diversity index (0.036), species evenness index (0.92) and species richness index (3.40) indicated a diverse distribution of the fungal species. Two-thirds of the identified fungal species showed significant preferences for their hosts. The host vulnerability was found to be significantly affected by storage facility, duration of storage, depot yard condition, treated or non-treated wood and shade facility. The findings of this work may help sawmill owners to utilize a scientific approach to management of logs and timber stored in depots, to minimize fungal decay before incurring any economic loss.

Ash dieback caused by Hymenoscyphus fraxineus was first recorded in Northern Ireland (NI) in November 2012. The disease was observed only on recently (<6 years) planted trees. An in-depth case study in 2015 of an ash plantation with severe symptoms indicated that many of the trees were infected at the time of planting. Apothecia were observed developing from pseudosclerotia beneath the epidermis of dead branches still attached to the tree, suggesting a possible mechanism whereby H. fraxineus could be disseminated without leaf or rachises infection. Apothecia also formed on roots, indicating that infections may also occur in the soil. Often young trees were killed by the formation of large basal lesions which did not arise from stem infections higher up. On first detecting the disease on the island of Ireland the Governments of NI and the Republic of Ireland published an “All-Ireland Chalara Control Strategy.” Part of that strategy was a ban on the importation of ash plants from regions where the disease was known to be present, to prevent the introduction of further inoculum, and the implementation of an ‘eradication and containment’ policy with the aim of preventing the establishment and spread of the disease. While these measures may have slowed disease establishment, they were ultimately unsuccessful and by 2018 ash dieback was widespread and established throughout the whole of NI in plantations and in the wider environment.

From June through October 2020, symptoms of a branch blight disease were observed on Physocarpus amurensis plants in Harbin City, Heilongjiang Province, China. Leaves on infected branches were chlorotic, with many raised, grey spots forming on the epidermis of diseased branches. Diseased twigs formed semi-buried, small, spherical pycnidia, which were initially light brown and later turned dark. The pathogen was isolated and its pathogenicity was verified with Koch's postulates. Based on morphological characteristics and DNA sequence data the pathogen was identified as Aplosporella longipes. This is the first report of A. longipes in China and the first report of it causing branch blight disease of P. amurensis.