Forest Pathology最新文献

Due to the intense ash dieback in Europe, which begins with the appearance of leaf infection, this study presents the results of the research on the impact of a selected isolate Pseudomonas koreensis R4.45P on the development of Hymenoscyphus fraxineus in the rachises of Fraxinus excelsior. Preliminary in vitro testing of P. koreensis R4.45P showed a statistically significantly lower growth of H. fraxineus compared to control cultures that were not exposed to this bacterium. The results of the in planta test on F. excelsior seedlings showed a statistically significant decrease in dieback occurrence and the length of necrotic lesions caused by H. fraxineus in rachises treated with P. koreensis R4.45P compared to untreated rachises. Additionally, leaf mortality in F. excelsior seedlings treated with P. koreensis R4.45P was statistically significantly lower. This study is the first to show the possibility of application of antagonistic bacteria P. koreensis R4.45P to effectively slow the initial stage of H. fraxineus development.

Pine pitch canker (PPC) emerged as a significant problem in 1945 in Southeastern USA. The causal agent, Fusarium circinatum, has spread widely and now occurs in pine forests and plantations worldwide. Fusarium circinatum causes damping off, shoot and tip die-back, and the death of seedlings in nurseries. Infection of mature trees leads to excessive resin bleeding on branches and main stems, sunken cankers with bark remaining attached, and finally, tree death. Arguably, F. circinatum is the most important pathogen of pine seedlings in many areas of the world. At least 67 species of Pinus, 18 Pinus hybrids, and 6 other non-pine tree species are susceptible to PPC. The selection and development of tree germplasm resistant to pathogens is considered the most robust approach to reduce losses to diseases. Genetic variation in resistance to F. circinatum certainly exists, even in generally very susceptible hosts, such as P. radiata. Exploiting genetic resistance as a tool to manage PPC requires screening large numbers of tree genotypes and fine-tuning efficient phenotyping protocols. The greater the number of genetic lines and replications, the higher the selection differentials and accuracy of the genetic parameter estimates. Recent advances in physiological and molecular techniques exploring the plant-pathogen interaction have expanded our understanding of genetic resistance mechanisms in pines to PPC and represent an added-value tool to support phenotypic selection. This review provides an overview of current knowledge on the molecular, physiological, and genetic basis of resistance to F. circinatum in pines and considers possibilities to improve the resistance of pines against the pathogen through breeding and selection.

Beech leaf disease (BLD) is an emerging threat to American beech (Fagus grandifolia Ehrh.) throughout North American forests attributable to the plant-parasitic nematode Litylenchus crenatae ssp. mccannii (Lcm). This study describes the impacts of BLD on bud retention and subsequent leaf production, associated symptoms, and the abundance of Lcm throughout the course of a single growing season within two natural forest stands exposed to different levels of disease pressure. We found that trees with 2+ years of BLD infection exhibited reductions in bud retention that represented 52.3% fewer buds per branch (m⁻¹) relative to a control stand that did not exhibit BLD symptoms in the previous year. Diseased trees also produced less foliage following spring bud break, corresponding to 67.8% fewer leaves per branch (m⁻¹). Bud death among diseased trees resulted in a decoupling from the expected foliage production derived from winter bud inventories. Through the characterization of BLD symptom expression among emerging leaves, including the presence of second flush leaves, we measured casting of severely symptomatic leaves coordinated with a marked increase in second flush leaves in the late summer. Nematodes counted within infected trees ranged from 83 to 9800 individuals per bud, while the proportion of live motile stages, eggs, and dead Lcm varied significantly between the spring and late-summer sampling periods. Together, our data provide important insights regarding the impact of a multi-year BLD infection on bud and foliage production, which has the potential to adversely affect tree carbon assimilation and long-term survival.

With an occurring shift in the tree species distribution, European beech (Fagus sylvatica L.) is becoming a perspective for forestry in the Baltics and Latvia in particular, despite presumed occurrence outside the natural distribution range. In 2023, a survey of European beech plantations established in 2020 in the central region of Latvia revealed that 13% of saplings had decline symptoms—branch dieback and top dieback in beech saplings, often accompanied by browning of leaves. An endophytic and anthracnose-causing ascomycete, Apiognomonia errabunda, was isolated from shoots of symptomatic beech saplings and potentially associated with the observed symptoms. Accordingly, this is the first molecularly approved report of this fungus in Latvia.

American beech (Fagus grandifolia) trees exhibiting symptoms of beech leaf disease (BLD) induced by the foliar nematode, Litylenchus crenatae, were found growing in Delmar, New York, USA, in 2019. Foliar symptoms included leaf drop, galling, and darkening associated with leaf curl. Bacterial isolates were cultured from infected leaf tissue and identified to genus by 16S rRNA gene sequencing and MALDI-TOF-MS profiling. In addition to many taxa with putatively environmental roles, strains of the genera Agrobacterium, Curtobacterium, Pantoea, Xanthomonas, as well as Erwinia and Pseudomonas were detected. Strains of the latter two genera have been previously associated with BLD, but isolates have not yet been identified at the species level. Phylogenetic trees generated from sequences of 16S rRNA and housekeeping genes (gyrB, rpoB, and rpoD) combined with MALDI-TOF-MS, showed that the isolates from nematode-infected leaves of American beech belonged to the known plant pathogenic species C. flaccumfaciens, E. billingiae, E. rhapontici, Pa. agglomerans, and X. arboricola. The species affiliation of strains showing close relatedness to A. skierniewicense, A. vaccinii, Pa. alfalfae, Pa. ananatis, Ps. amygdali, Ps. cerasi, and Ps. syringae requires further support. The identities of other bacteria isolated from the same samples are also provided.