Forest Pathology最新文献

Needle diseases caused by pathogens within Rhytismataceae are increasing in frequency globally where pines are either a predominate species or are grown commercially, and yet remain poorly understood. Here, we provide background information on the current knowledge and management strategies of needle pathogens in the Rhytismataceae and discuss research opportunities using molecular tools to fill knowledge gaps. Many of the aggressive needle pathogens within this group lack morphological features to delimit species and are difficult to grow in axenic cultures, which complicates scientific investigations. Molecular research has greatly advanced knowledge of this unique group of pathogens. Nucleotide sequences from multiple gene loci identified greater diversity within this group of pathogens than previously thought, as new and cryptic species are being discovered in broader geographic regions. High throughput sequencing and analyses revealed that an endophytic lifestyle is a common trait among fastidious if not obligate needle pathogens within Rhytismataceae. Further, molecular analyses showed the impact these pathogens have on the diversity of endophytic microbiota is underestimated. Early detection in healthy-looking needles using PCR-based markers greatly improves capabilities for disease diagnosis and monitoring. Despite growing number of molecular studies on Rhytismataceae needle pathogens, fundamental questions on the taxonomy, phylogeny, ecology and pathology of many Rhytismataceae needle pathogens remain unanswered. Nonetheless, with the projected changes in the occurrence and severity of Rhytismataceae pathogens, increased accessibility to molecular tools vastly expands the potential to gain more insights into understudied needle pathosystems to help define and address its impact under changing environments and consequently inform forest disease management more effectively.

Sydowia polyspora is a common fungal species living on conifers, often occurring as an epiphyte or endophyte on asymptomatic plants and in seeds. The fungus may become pathogenic under abiotic or biotic stress conditions. It is often associated with current season needle necrosis and shoot dieback on conifer species, especially Abies spp. and Pinus spp. throughout Europe and North America. The conifer Pinus brutia is common and widely distributed in Türkiye and is frequently used in reforestation. The work described here aimed to investigate the S. polyspora associated with needle necrosis and shoot dieback in five different Pinus brutia stands located in Denizli-Türkiye, to determine the severity of the disease and to reveal the pathogenicity of this agent in P. brutia seedlings. For this purpose, fungal isolations from symptomatic P. brutia needles were carried out in five different stands. In total, 68 S. polyspora isolates were obtained, each from a different tree from which macroscopic-microscopic morphological characterization was made and molecular characterization was done using the internal transcribed spacer (ITS) region. BLAST analysis of the ITS sequences confirmed the identification of the isolates, with 99–100% similarity to previously reported sequences of S. polyspora. Disease incidence and severity were assessed in five P. brutia stands. The disease incidence ranged between 38% and 62% (mean = 47%) while disease severity varied among sites. Pathogenicity studies were carried out on 2-year-old P. brutia seedlings using obtained isolates. Infection frequency in inoculated shoots was 90%. The pathogenicity tests, followed by re-isolation of the fungus from symptomatic shoots clearly demonstrated that S. polyspora played a role in the development of needle necrosis and shoot dieback in P. brutia stands. To the best of our knowledge, this is the first report of current season needle necrosis and shoot dieback on P. brutia caused by S. polyspora in Türkiye.

Caucasian alder (Alnus subcordata) is among the major constituents of the Hyrcanian forests extending all along the southern coast of the Caspian Sea in northern Iran. An angular leaf spot with a yellowish chlorotic halo has attained a widespread occurrence throughout the forest and suburban areas of the northern provinces including Guilan, Mazandaran and Golestan. Strains of a Xanthomonas sp. were consistently isolated from the symptomatic leaves of A. subcordata. Colonies of the isolates were yellow circular, convex and mucoid on nutrient agar containing glucose or sucrose. In multilocus sequence analysis using the genes gyrB, rpoD, dnaK, gltA, fyuA and gapA, the representative isolates occupied a clade shared by the known pathovars of Xanthomonas arboricola. The isolates were relatively heterogeneous phenotypically, but more so in their rep-PCR fingerprints. Pathogenicity of several isolates was confirmed on seedlings of A. subcordata and Alnus rhombifolia, whereas Alnus cordata, Alnus glutinosa and Alnus crispa appeared not to be susceptible. Based on these characteristics, the isolates causing angular leaf spots of Caucasian alder appear to represent a novel pathovar of X. arboricola.

Ceratocystis wilt is one of the most harmful diseases affecting eucalyptus crops and is associated with species of the complex Ceratocystis fimbriata sensu lato. This pathology leads to the obstruction of the vascular system in infected trees, resulting in symptoms such as branch wilting and death. The wood affected by the pathogen exhibits discolouration and changes in its chemical composition, which can impact the pulping process. Therefore, the objective of this work is to investigate the impact of ceratocystis wilt on growth and the pulping process when sampling whole diseased trees. For this, healthy and diseased eucalyptus trees at the harvest age of 7 years were cut down, and their dendrometric variables (diameter at breast height, height and volume) and disease severity (basal discolouration area and volume of discoloured tissue) were measured. All tree trunks, classified into different severity classes, were sampled individually, peeled, chipped and subjected to Kraft cooking (Kappa number 18 ± 0.5). Diseased trees, under the evaluated condition, exhibited an average volume of 2.5% with discolouration and a reduction in the volumetric growth of 18.1%. The wood from diseased trees showed no significant differences in the Kraft cooking variables when compared to healthy trees. This result suggests that ceratocystis wilt reduces the volumetric growth of affected trees; however, due to the low proportion of symptomatic wood observed, the utilization of wood from diseased trees does not influence pulping and can be used in the pulp production process.

We report observations of Onnia subtriquetra on bishop pine (Pinus muricata) and shore pine (Pinus contorta var. contorta) from north coastal California. Our identification of this fungus is supported by molecular information, morphological characteristics, and and a description of the observed range of the fungus on the West Coast. These observations represent an expansion of the geographic and host ranges of Onnia subtriquetra, which on the observed sites is generally associated with declining tree condition and the presence of other native forest pathogens and insects.

Sweet chestnut (Castanea sativa) is an ecologically and economically valuable tree species worldwide. Various pathogens, both endemic or introduced, cause severe damage or death to chestnut trees. Chestnut blight, caused by the fungus Cryphonectria parasitica, is one of the most devastating plant diseases known which influences chestnut trees in all major cultivation regions. The work presented here aimed to investigate how the incidence of chestnut blight varied between trees growing at two altitudes (200–400 m vs. 400–600 m) and to determine the impact of chestnut blight on tree-ring width, morphology and anatomy of C. sativa trees. The incidence of C. parasitica infections was greater at 200–400 m than at 400–600 m. Greater stem diameters were found at 200–400 m than at 400–600 m. There were no differences in stem diameters and heights, however, between healthy and C. parasitica infected chestnut trees. The anatomical characteristics of wood were also compared between healthy and C. parasitica-infected chestnut trees. Fibre cell traits (length/width, lumen width, lumen area) were higher in healthy trees than in C. parasitica-diseased trees. Vessel diameters were greater in infected compared with healthy trees. Tree ring widths and wood anatomical characteristics therefore were significantly influenced by C. parasitica infections.

Hornbeam (Carpinus betulus) is an economically significant tree species, serving as a valuable resource for timber and ornamental wood products. It plays a crucial ecological role within forest communities and exhibits wide distribution across Central Europe. During October 2022 and March 2023, we encountered instances of declining hornbeam trees in Hungary and Slovakia. In both cases, characteristic symptoms associated with Cryphonectria canker were observed. Subsequent morphological and molecular-genetic analyses of fungal samples and isolates confirmed their identification as the recently described species Cryphonectria carpinicola. This study represents the first documented report of this pathogen in Hungary and Slovakia, contributing to our understanding of its presence and impact in Central Europe.

Beech leaf disease (BLD) is a foliar disease of American Beech (Fagus grandifolia L.) causally linked to the nematode Litylenchus crenatae mccannii and has rapidly spread throughout central and northeastern North America. This study aimed to characterize the anatomical and physiological differences between asymptomatic and symptomatic leaves to provide evidence for a mechanistic link between abnormal leaf development associated with BLD and the long-term decline of affected trees. We found that leaf mass per area (LMA) and leaf thickness were 45% and 249% higher in symptomatic regions, respectively. The difference in leaf thickness was largely attributable to the spongy mesophyll being 410% thicker in symptomatic as compared with asymptomatic regions of the leaves, but palisade mesophyll and abaxial epidermal tissues were also thicker in symptomatic regions. While major vein density was not significantly different, minor vein density was significantly lower in symptomatic regions, suggesting that the effects on leaf development occur after the formation and initial development of first- and second-order veins. Stomatal density was also lower in symptomatic leaves. Maximum photosynthetic rates were approximately 61% lower in symptomatic leaves and respiration rate increased as the percentage of affected leaf tissue increased. Collectively, our data show reduced photosynthetic capacity, increased respiration rates, and higher leaf construction costs, which will likely have a negative, long-term impact on the carbon balance of trees affected by BLD.

Torreya grandis cv. Merrillii is an important economic tree widely cultivated in hilly subtropical areas in China and some parts of Japan and Korea. Crown and root rot was found on T. grandis in Zhejiang Province of China. Three isolates with similar morphology were isolated from diseased samples, and used for identification and pathogenicity tests. The pathogenicity of the isolates was confirmed by fulfilling Koch's postulates. The pathogen was identified as Fusarium commune based on morphological characteristics and phylogenetic tree constructed by combining ITS and TEF-1α gene sequences. This is the first report of F. commune causing crown and root rot on T. grandis in China.

Acacia crassicarpa is a tropical tree species native to Australia, West Papua and Papua New Guinea, which has been widely used to establish plantations in the lowland humid tropics of Sumatra and Kalimantan. These trees, able to grow on sites having relatively poor nutrition, have been relatively free of serious disease problems. A rust disease infecting the phyllodes of A. crassicarpa has recently been encountered in plantations in various areas of Indonesia and Malaysia where they are not native. In this study, the rust was collected and identified as Endoraecium violae-faustiae using DNA sequence analysis based on the internal transcribed spacer (ITS) region of the rDNA. This is the first record of the rust outside its native range. Damage at present appears to be relatively mild but the pathogen could become important in the future.