Sarah L. Boggess

Vascular streak dieback (VSD) has emerged as a major threat to woody ornamental production in the United States (U.S.), currently affecting at least 50 tree and shrub species across 25 botanical genera in at least twelve U.S. states. The putative causal agent, here termed the VSD‐associated Ceratobasidiaceae lineage ( Csp ), presents diagnostic challenges due to its fastidious growth requirements and vascular colonization pattern. Here, we integrate genomics‐guided marker discovery with multi‐platform genome‐anchored tools (SSR, TaqMan qPCR, and LAMP that target unique genomic regions identified through comparative genomics) to deliver a field‐deployable, genome‐anchored toolkit for detection and genotyping of Csp across nurseries and landscapes. We evaluated the performance of these tools using 103 samples representing DNA isolated from 64 VSD‐symptomatic plants or their fungal isolates and 39 non‐target Ceratobasidiaceae outgroups. Genome assembly of Illumina reads yielded ten informative microsatellite markers with an overall amplification success rate of 95.8% (91.7%–100.0% across Csp samples). These markers demonstrated strong performance in distinguishing the Csp samples from the outgroups. Among the three TaqMan probes developed, VSD048 exhibited superior performance with 100% detection across Csp samples, characterized by cycle threshold (C _T ) values of 26.8 ± 4.2, and no cross‐reactivity with C. theobromae or other Ceratobasidiaceae species. A multi‐laboratory ring trial confirmed the reproducibility of the VSD048 TaqMan assay across various testing platforms. The loop‐mediated isothermal amplification (LAMP) assay targeting the Csp ‐unique region achieved a sensitivity of 0.82 [95% CI 0.68–0.968] and specificity of 1.00 [95% CI 1.00–1.00], with a practical detection threshold of approximately 25 copies of the target region. Our molecular survey of the disease revealed a surprisingly broad host range beyond Cercis canadensis (Eastern redbud), encompassing eight additional genera, and confirmed its geographical distribution across the eastern and midwestern U.S. These validated molecular tools provide rapid, sensitive, and specific detection methods for Csp surveillance and management. The field‐applicable LAMP assay and laboratory‐based TaqMan/SSR protocols offer complementary approaches for different diagnostic scenarios, thereby enabling early detection and supporting efforts to limit the spread of this emerging pathogen in nursery and landscape settings.

Background: The North American-native ornamental tree, flowering dogwood ( Cornus florida L.), has a showy bract display that can range in color from white to pink to deep red. Although many trees have white bracts, there is consumer demand for novel pigmentation in the bracts combined with other traits of interest. Because the genetic basis of all traits in flowering dogwood is unknown, combining them using traditional breeding efforts is time, labor, and space-intensive. Results: We developed foundational genomic resources to establish marker-assisted selection within flowering dogwood breeding. We generated diploid, chromosome-scale, annotated genome assemblies for one pink-bracted and red-leafed tree and one white-bracted and green-leafed tree. Additionally, a phenotyping protocol for bract color and presence/absence diagnostic SNPs for bract and leaf color were established. We leveraged these resources to evaluate linkage associations and differential gene expression related to anthocyanin biosynthesis to identify candidate genes regulating bract and leaf pigmentation. Within a 14 Mb locus we identified 14 anthocyanin-related genes. Two genes, with MYB ( g19533 ) and RING finger ( g19556) binding domains, had both differential gene expression and variants with the expected segregation pattern. Conclusions: These candidate genes, diagnostic SNPs, and genomic resources will be valuable in combining pink-red bracts with other traits to advance flowering dogwood breeding.

In July 2023, chestnut tree mortalities were reported in the parc châtaigneraie, situated in the Akfadou mountain range, in Tizi Ouzou, Algeria. Dead sweet chestnut (Castanea sativa) trees exhibited symptoms including crown dieback, withered and dried leaves clinging to the branches, trunk and branch cracks and cankers, with a proliferation of epicormic shoots under the cankered areas (Fig 1). Examination of the cankers with a hand magnifying lens, exposed orange masses, erupting from under the bark. Cankers were found on the lower part of the trunk, with few occurrences on the branches. Flat mycelial fans were observed throughout the bark. Samples of infected wood were collected and subjected to further analysis in the laboratory. Close observation of fragments of infected wood under the stereomicroscope showed orange to dark orange fruiting structures (pycnidia), originating in the cambium, which showed a discoloration in cross section. After incubation (24 hours) in a humid chamber, twisted yellowish tendrils oozing from the pycnidia were observed (Fig 2). Pycnidia were isolated from the bark and transferred onto full strength potato dextrose agar (PDA). Fast growing whitish then turning to yellow-orange colonies developed within 5 days, with a growth rate of 7 mm/day at 30°C. Conidiospores were hyaline, aseptate, oblong to cylindrical, 2-4 x 1.5-2 µm in size. Total genomic DNA was extracted and the Elongation factor 1a (EF-1a) (Carbone & Kohn, 1999) and Beta-tubulin (βT1) (Glass & Donaldson, 1995) gene regions were amplified using the Phire Direct PCR kit (ThermoFisher) and PCR amplicons were subsequently sequenced. The EF-1a (PQ416673) and βT1 (PQ416670) sequence identity was determined using the Genbank database with 99.69% and 100% identity to Cryphonectria parasitica (OM112254.1 and MK578073.1) respectively. Based on disease symptoms, cultural and morphological characters, and DNA sequence similarity, the fungal pathogen was identified as Cryphonectria parasitica. Koch's postulates were performed to confirm the pathogenicity of C. parasitica by using chestnut tree detached twigs as described in Hunter et al. (2013). Twelve Chestnut twigs (20 cm long and 2 cm in diameter) were surface sterilized then put to dry in a laminar hood under a constant air flow for 10 minutes. Seven day old mycelial plugs from cultures of C. parasitica were used to inoculate two branches with three replicates. The six controls were inoculated with PDA plugs. After 5 weeks incubation at 20°;C (9/15 hours light/dark regime, respectively), canker zones developed around the inoculation point, from which the pathogen was reisolated. The recovered C. parasitica isolate was confirmed using methods described above. The resulting consensus sequences of the recovered pathogen matched C. parasitica with EF-1a 99.71-100% identity (PQ416674, PQ416675) and βT1 100% identity (PQ416671, PQ416672). This represents the first report of C. parasitica in Algeria, and the second report in Africa (EPPO, 1994). According to forestry archives, the chestnut groves of Tizi-Ouzou infected with C. parasitica, come from the Cévennes, in France (Rabhi & Messaoudene, 2018). Further field surveys need to be conducted to detect the presence of this disease in other chestnut orchards across Algeria, and phytosanitary regulation measures must be undertaken in order to counter the spread of this disease in Algeria and the North African region.

The North American-native ornamental tree, flowering dogwood (Cornus florida L.), has a showy bract display that can range in color from white to pink to deep red. Although many trees have white bracts, there is consumer demand for novel pigmentation in the bracts combined with other traits of interest. Because the genetic basis of all traits in flowering dogwood is unknown, combining them using traditional breeding efforts is time, labor, and space-intensive. We developed foundational genomic resources to establish marker-assisted selection within flowering dogwood breeding. We generated diploid, chromosome-scale, annotated genome assemblies for one pink-bracted and red-leafed tree and one white-bracted and green-leafed tree. Additionally, a phenotyping protocol for bract color and presence/absence diagnostic SNPs for bract and leaf color were established. We leveraged these resources to evaluate linkage associations and differential gene expression related to anthocyanin biosynthesis to identify candidate genes regulating bract and leaf pigmentation. Within a 14Mb locus we identified 14 anthocyanin-related candidate genes. Two genes, with MYB (g19533) and RING finger (g19556) binding domains, had both differential gene expression and variants with the expected segregation pattern. These resources will be valuable in combining pink-red bracts with other traits to advance flowering dogwood breeding.

The increasing prevalence of fungal diseases poses major threats to agricultural productivity and biodiversity, particularly in the context of plant-pathogen interactions. Understanding the mechanisms by which pathogens such as Discula destructiva cause disease and losses in dogwoods, important forest plants and nursery ornamental crops, is crucial for developing effective management strategies. This study focuses on the enzymatic activities of D. destructiva, the causal agent of dogwood anthracnose, and their role in facilitating pathogenicity in Cornus spp. We hypothesized that D. destructiva produces higher levels of extracellular hydrolytic and oxidative enzymes compared with other Discula species, which could enhance its ability to invade and degrade host plant tissues. Our findings revealed that isolates of D. destructiva exhibit elevated enzymatic activities, specifically with abundant polyphenol oxidase activity. Additionally, we assessed the influence of environmental factors, such as pH and medium composition, on pathogen growth, demonstrated that optimal growth occurs at pH 4.5, whereas alkaline conditions inhibited growth dynamics. These insights suggest that managing environmental conditions or fungicide formulations could be an effective strategy for controlling the spread of dogwood anthracnose pathogen, thereby emphasizing the importance of enzymatic profiles in fungal pathogenicity.

Understanding the diversity and ecological evolutionary history of plant species is crucial for addressing the current biodiversity crisis and comprehending the processes by which organisms fill ecological and geographic spaces. In this study, we present a comprehensive analysis of the diversity and evolutionary history of Diphasiastrum digitatum Holub from the lycophyte lineage of plants, using microsatellite genotyping data and biogeographic analyses. Based on the available transcriptome assembly, we generated numerous markers and utilized 13 robust microsatellite markers to genotype a collection of 402 specimens from the Eastern US (VT; VA; NC; TN). In accordance with the accepted phylogeny, cross‐amplification tests demonstrated a closer relationship between D. digitatum and Diphasiastrum spp. compared with Lycopodium spp. Furthermore, the population genetics analyses identified two genetic clusters within the D. digitatum collection and suggested ongoing divergence and expansion. Isolation‐by‐distance analysis indicated that geographic distance had a minimal effect on differentiation, whereas environmental variables related to water regime were strongly associated with the genetic variance. Ecological niche modeling showed a post‐Last Glacial Maximum expansion of D. digitatum from southern refugia, corroborating a similar evolutionary scenario based on our microsatellite data. Overall, this study provides valuable insights into the evolutionary history of clubmosses and highlights the migration events and the environmental factors that shaped their current distribution.

Helianthus verticillatus (Asteraceae), a whorled sunflower, is a perennial species restricted to a few locations in the southeastern United States and is now considered endangered. Therefore, restoring and protecting H. verticillatus as a species is a priority. This study introduces a highly efficient in vitro adventitious plant regeneration system from leaf explants, utilizing five diverse specimens of H. verticillatus, each representing distinct genotypes with phenotypic variations in leaf and stem morphology. Key factors influencing in vitro morphogenesis, including genetic constitution, explant source, and plant growth regulators (PGRs), were identified. The study revealed a remarkably strong genotype-dependent impact on the regeneration efficiency of the investigated H. verticillatus genotypes, ranging from a lack of regeneration to highly effective regeneration. The selection of two genotypes with varying regeneration abilities provides valuable models for genetic analyses, offering insights into factors influencing the regeneration potential of this endangered species. Optimum adventitious shoot regeneration results were achieved using Murashige and Skoog basal media (MS) supplemented with 8.8 µM N6-benzyladenine (BA) and 1.08 µM α-naphthalene acetic acid (NAA). This combination yielded the highest adventitious shoot production. Subsequent successful rooting on ½ MS medium without PGRs further solidified the efficiency of the developed protocol. Regenerated plantlets, demonstrating robust shoots and roots, were successfully acclimatized to greenhouse conditions with a 95% survival rate. The protocol developed in this study is the first such report for this endangered species and is expected to contribute to future genetic manipulation and modification studies.

"Two New Cultivars of Cornus kousa: Melissa’s Mountain Snowfall and Sarah’s Mountain Pixie" published on Jan 2024 by American Society for Horticultural Science.

Whorled sunflower, Helianthus verticillatus Small, is an endangered (U.S. Fish and Wildlife Service 2014) perennial sunflower species indigenous to the southern United States (Matthews et al. 2002;...

Whorled sunflower, Helianthus verticillatus Small (Asteraceae), is a federally endangered species (US Fish and Wildlife Service, 2014) growing in only a few locations in Tennessee, Georgia, Mississ...