Forest Pathology最新文献

Frangipani (Plumeria spp.: Apocynaceae) is a small ornamental tree native to Mexico, susceptible to significant diseases such as anthracnose and foliar blight in hot, dry environments. Understanding the diversity of pathogens responsible for these diseases is crucial for developing effective disease management strategies. This study aimed to identify the pathogens responsible for these diseases. In February 2020 and 2021, symptoms of anthracnose and foliar blight were observed on frangipani plants in recreational areas of Morelos and Sinaloa, Mexico. Isolations from diseased leaf tissue resulted in the recovery of 12 Colletotrichum isolates from P. rubra and 18 Alternaria isolates from P. obtusa. After morphotype grouping, a representative isolate from each group was identified by morphology and phylogenetic reconstruction (ITS, act, gapdh, rpb2 and tef1) as Colletotrichum karstii, Colletotrichum siamense, Alternaria destruens and Alternaria burnsii. For pathogenicity testing, a conidial suspension was sprayed onto the leaves of 90-day-old plants, while control plants were sprayed with sterile distilled water. All inoculated fungi were pathogenic, reproducing the characteristic symptoms of the disease, while control plants remained symptomless. The fungi recovered from symptomatic plants were morphologically identical to the inoculated fungi, fulfilling Koch's postulates. This is the first report of A. burnsii and A. destruens causing foliar blight in P. obtusa, and C. siamense and C. karstii causing anthracnose in P. rubra. These findings contribute valuable insights for developing effective disease management strategies.

Lecanosticta acicola, the causal agent of brown spot needle blight, is a known pine needle pathogen. During the past decades, it has spread in Northern Europe, including the Baltics, where it has mainly infected exotic pines. This study presents novel data on the occurrence of the pathogen on introduced, as well as on further spread of the pest to the native pine species in Latvia. In the autumn of 2022, infection of L. acicola was discovered on several young native Scots pine (Pinus sylvestris) stands throughout Latvia, and in a commercial nursery, thus signifying the transition to a native host with high potential for wider expansion. The transmission of the pathogen to the local pine populations could accelerate the spread of the pathogen and decrease the vitality of pines in the Baltics in the future. The fungus was identified by molecular PCR-based methods; conidia were found only on a few pines in surveyed stands, as symptom severity was still low (mostly latent infection). Nevertheless, the observed behaviour of the pathogen implies the establishment and presumed invasion in the native forest areas, and thus the emergence of additional forestry risks.

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.