Novel Pathogen-Plant Host Interaction: Colletotrichum jiangxiense and Fraxinus americana L. (White Ash) in a Sentinel Garden in China.

Fraxinus americana L. (white ash), a native North American tree commonly cultivated for its ornamental qualities, displayed symptoms of leaf spot disease in a sentinel garden located in Nanjing, Jiangsu, China, in 2022. This disease led to premature leaf shedding, adversely affecting the plant's growth and substantially diminishing its ornamental value. Potential fungal pathogens were isolated from the diseased leaves and the subsequent application of Koch's postulates confirmed the pathogenicity of the fungal isolates (BL-1, BL-2). Through a combination of multi-locus phylogenetic analysis, including ITS, ACT, ApMat, CAL, CHS-1, GAPDH, and TUB2, alongside morphological assessments, the fungus was conclusively identified as Colletotrichum jiangxiense. This represents the first record of C. jiangxiense affecting white ash, highlighting the important role of sentinel gardens in uncovering novel pathogen-plant host interactions.

Comparison of Diplodia Tip Blight Pathogens in Spanish and North American Pine Ecosystems.

Diplodia tip blight is the most ubiquitous and abundant disease in Spanish Pinus radiata plantations. The economic losses in forest stands can be very severe because of its abundance in cones and seeds together with the low genetic diversity of the host. Pinus resinosa is not genetically diverse in North America either, and Diplodia shoot blight is a common disease. Disease control may require management designs to be adapted for each region. The genetic diversity of the pathogen could be an indicator of its virulence and spreading capacity. Our objective was to understand the diversity of Diplodia spp. in Spanish plantations and to compare it with the structure of American populations to collaborate in future management guidelines. Genotypic diversity was investigated using microsatellite markers. Eight loci (SS9-SS16) were polymorphic for the 322 isolates genotyped. The results indicate that Diplodia sapinea is the most frequent Diplodia species present in plantations of the north of Spain and has high genetic diversity. The higher genetic diversity recorded in Spain in comparison to previous studies could be influenced by the intensity of the sampling and the evidence about the remarkable influence of the sample type.

Molecular characterization and phylogenetic analyses of Lophodermella needle pathogens (Rhytismataceae) on Pinus species in the USA and Europe.

Increasing prevalence of conifer needle pathogens globally have prompted further studies on pathogen identification and a better understanding of phylogenetic relationships among needle pathogens. Several Lophodermella species can be aggressive pathogens causing needle cast in natural pine forests in the USA and Europe. However, their relationships with other Rhytismataceae species have historically been based on similarities of only limited phenotypic characters. Currently, no molecular studies have been completed to elucidate their relationships with other Lophodermella needle pathogens. This study collected and sequenced three gene loci, namely: internal transcribed spacer, large ribosomal subunit, and translation elongation factor 1-alpha, from five Lophodermella needle pathogens from North America (L. arcuata, L. concolor, L. montivaga) and Europe (L. conjuncta and L. sulcigena) to distinguish phylogeny within Rhytismatacaeae, including Lophophacidium dooksii. Phylogenetic analyses of the three loci revealed that all but L. conjuncta that were sampled in this study consistently clustered in a well-supported clade within Rhytismataceae. The multi-gene phylogeny also confirmed consistent nesting of L. dooksii, a needle pathogen of Pinus strobus, within the clade. Potential synapomorphic characters such as ascomata position and ascospore shape for the distinct clade were also explored. Further, a rhytismataceous species on P. flexilis that was morphologically identified as L. arcuata was found to be unique based on the sequences at the three loci. This study suggests a potential wider range of host species within the genus and the need for genetic characterization of other Lophodermella and Lophophacidium species to provide a higher phylogenetic resolution.

Sap Beetles (Coleoptera: Nitidulidae) in Oak Forests of Two Northeastern States: A Comparison of Trapping Methods and Monitoring for Phoretic Fungi.

Oak wilt is slowly expanding in the northeastern United States. Several nitidulid beetle species are known vectors of the fungus [Bretziella fagacearum (Bretz) Z. W. De Beer, Marinc., T. A. Duong, and M. J. Wingf (Microascales: Ceratocystidaceae)] that causes this disease, acquiring spores from fungal mats on infected trees and transmitting them to uninfected trees. Survey and fungal isolation from captured nitidulid beetles could be an important tool for detecting the presence of this disease in a geographic area not previously known to have oak wilt. In preparation for monitoring activities in such areas, two trapping studies were conducted in the northeastern United States: 1) trap test comparing the efficacy of wind-oriented pipe, multiple-funnel, and modified pitfall traps for nitidulids and 2) wet and dry collection cup comparison. Lures were a combination of nitidulid pheromones and fermenting liquid. Results support the use of multiple-funnel traps over the other two trap types, for both targeted species-specific surveys and community sampling. More total nitidulids, Colopterus truncatus (Randall), and Glischrochilus fasciatus (Olivier) were captured in wet collection cups compared with dry cups. Twenty-seven fungal species were isolated, none of which were B. fagacearum. Many fungi isolated from beetles were plant pathogens, indicating that in addition to the oak wilt fungus, sap beetles may contribute to the spread of other plant diseases.

Emergence of white pine needle damage in the northeastern United States is associated with changes in pathogen pressure in response to climate change.

The defoliation of the eastern white pine (Pinus strobus) across the northeastern United States is an escalating concern threatening the ecological health of northern forests and economic vitality of the region's lumber industry. First documented in the spring of 2010 affecting 24 328 hectares in the state of Maine, white pine needle damage (WPND) has continued to spread and is now well established in all New England states. While causal agents of WPND are known, current research is lacking in both sampling distribution and the specific environmental factor(s) that affect the development and spread of this disease complex. This study aims to construct a more detailed distribution map of the four primary causal agents within the region, as well as utilize long-term WPND monitoring plots and data collected from land-based weather stations to develop a climatic model to predict the severity of defoliation events in the proceeding year. Sampling results showed a greater distribution of WPND than previously reported. WPND was generally found in forest stands that compromised >50% eastern white pine by basal area. No single species, nor a specific combination of species had a dominating presence in particular states or regions, thus supporting the disease complex theory that WPND is neither caused by an individual species nor by a specific combination of species. In addition, regional weather data confirmed the trend of increasing temperature and precipitation observed in this region with the previous year's May, June, and July rainfall being the best predictor of defoliation events in the following year. Climatic models were developed to aid land managers in predicting disease severity and accordingly adjust their management decisions. Our results clearly demonstrate the role changing climate patterns have on the health of eastern white pine in the northeastern United States.

Impact of White Pine Blister Rust on Resistant Cultivated Ribes and Neighboring Eastern White Pine in New Hampshire.

To determine the impact of white pine blister rust (WPBR) following the recent breakdown of the Cr resistance dominant gene in cultivated Ribes spp., 255 plants of 19 Ribes cultivars and 445 neighboring eastern white pine (Pinus strobus) from 42 sites across New Hampshire were evaluated. Of the 19 Ribes cultivars evaluated, 15 were WPBR resistant, and 4 of these were labeled as black currant (Ribes nigrum) with the Cr gene (Cr Ribes cultivars). Incidence of WPBR ranged from 0 to 88% for WPBR-resistant Ribes cultivars. Mean WPBR severity was 14 and <6% of leaf area for Cr Ribes and partially resistant cultivars, respectively. The presence of Cronartium ribicola was confirmed on 17 of the 19 Ribes cultivars screened with polymerase chain reaction analysis and DNA sequencing. Reference accessions of Cr Ribes cultivars from the Canadian Clonal Genebank were successfully infected with C. ribicola inoculum collected in New Hampshire from Cr Ribes cultivars and P. strobus, confirming that the vCr race of C. ribicola that has overcome the Cr resistance dominant gene in cultivated Ribes spp. is present in New Hampshire. The probability of finding pine trees with WPBR was greater for trees neighboring infected Cr Ribes cultivars (0.18) than trees neighboring WPBR-free Ribes cultivars (0.02). Results from this study suggest that the breakdown of Cr-based resistance in Ribes spp. poses a threat to the white pine resource and to cultivated Ribes production.

Quantification of Conidia of Diplodia spp. Extracted from Red and Jack Pine Cones.

Frequency of detection and inoculum production by the conifer shoot blight and canker pathogens Diplodia pinea and D. scrobiculata on cones of red pine (Pinus resinosa) and jack pine (P. banksiana) were studied. Cones were collected from the ground and from canopies of red and jack pine trees in mixed stands at three sites in each of two different locations during two consecutive summers in Wisconsin. Conidia were extracted in water, quantified, germination tested, and the Diplodia species present was determined using molecular methods. At least one pathogen was detected from each tree at each site in both years. Overall, more conidia were extracted from cones from canopies than cones from the ground and from red pine cones than jack pine cones. Both total numbers of conidia extracted and proportions of cones yielding D. pinea or D. scrobiculata varied by location and pine species. Cones from either the ground or canopies can be used for surveys to detect Diplodia spp. at a given site but cones from canopies may be more useful to determine the relative abundance of potentially available inoculum of these pathogens.