Robert N. Trigiano

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.

Flowering dogwood ( Cornus florida L.) and Asian dogwood ( Cornus kousa F. Buerger ex Hance) are popular deciduous ornamental trees native to a wide range of the eastern and southeastern United States and East Asia, respectively. Anthocyanin pigments enhance desirable pink or dark red colored bracts in dogwoods. Although anthocyanin biosynthesis is one of the best‐studied biological processes in nature, genomic and genetic resources to understand the molecular regulation of its synthesis in dogwoods are still lacking. Two classes of genes control anthocyanin production; both structural genes and MYB transcription factors may function as positive or negative regulators of anthocyanin biosynthesis. To reveal the molecular mechanisms that govern color production in ornamental dogwoods, mature bracts of three cultivars of C. florida (white bracts: “Cloud Nine”; red bracts: “Cherokee Brave,” and “Cherokee Chief”) and two cultivars of C. kousa (light green bracts: “Greensleeves” and midtone pink bracts “Rosy Teacups”) were sampled when color was maximally visible. Differential gene expression analysis of the RNAseq data identified 1156 differentially expressed genes in C. florida and 1396 in C. kousa . Phylogenetic analysis with functional orthologues in other plants grouped the candidate R2R3‐MYB identified in this study into two distinct subgroups. CfMYB2 , CfMYB3 , and CkMYB 2 belong to Subgroup 4, whereas CfMYB1 80 and CkMYB1 clustered in Subgroup 5. Genes in the former group repress anthocyanin and proanthocyanidin synthesis in flowering and Asian dogwoods, whereas genes in the latter increase it. Our study contributes to understanding processes behind anthocyanin production and lays the foundation for the future development of molecular markers for faster development of desirable red‐bracted dogwoods.

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.

Flowering dogwood ( Cornus florida L.) and Asian dogwood ( C. kousa F. Buerger ex Hance) are popular deciduous ornamental trees native to a wide range of the eastern and southeastern United States and East Asia, respectively. Anthocyanin pigments enhance desirable pink or dark red colored bracts in dogwoods. Although anthocyanin biosynthesis is one of the best-studied biological processes in nature, genomic and genetic resources to understand the molecular regulation of its synthesis in dogwoods are still lacking. Two classes of genes control anthocyanin production; both structural genes and MYB transcription factors may function as positive or negative regulators of anthocyanin biosynthesis. To reveal the molecular mechanisms that govern color production in ornamental dogwoods, mature bracts of three cultivars of C. florida (white bracts: ‘Cloud Nine’; red bracts: ‘Cherokee Brave’ and ‘Cherokee Chief’) and two cultivars of C. kousa (light green bracts: ‘Greensleeves’ and mid-tone pink bracts ‘Rosy Teacups’) were sampled when color was maximally visible. Differential gene expression analysis of the RNAseq data identified 1,156 differentially expressed genes in C. florida and 1,396 in C. kousa . Phylogenetic analysis with functional orthologues in other plants grouped the candidate R2R3-MYB identified in this study into two distinct subgroups. CfMYB2 , CfMYB3 , and CkMYB 2 belonged to subgroup 4, whereas CfMYB1 80 and CkMYB1 clustered in subgroup 5. The former repress anthocyanin and proanthocyanidin synthesis in flowering and Asian dogwoods, whereas the latter increase it. Our study contributes to understanding processes behind anthocyanin production and lays foundation to future development of molecular markers for faster development of desirable red-bracted dogwoods.

Eastern redbud (Cercis canadensis L.) is a popular and high-value woody ornamental plant native to the Eastern and South Central United States. In recent years, redbud production in the Southeastern United States has been greatly affected by a novel threat: vascular streak dieback (VSD). Infected plants exhibit a common set of symptoms, including leaf scorch, tip dieback, and vascular streaking that creates a marbled pattern in stem cross-section. Based on both conventional diagnosis and molecular identification, it has been found that the fungus Ceratobasidium sp. D.P. Rogers (Csp) is consistently associated with VSD-symptomatic eastern redbuds. However, the causal agent(s) of VSD has not yet been conclusively confirmed. Although eastern redbud has been the most frequently identified host tree, more than 25 other native plant genera have been confirmed to have VSD associated with Csp. The near-obligate nature of this fungus has made it challenging to culture, extract DNA, and conduct further studies to confirm its pathogenicity. This article highlights the emerging challenges of VSD, focusing on the following: (i) the recent history of VSD; (ii) the increasing importance of VSD to woody ornamental nursery production in the United States; (iii) the currently available protocols for isolating, culturing, storing, and maintaining the putative causal agent; (iv) the rapid molecular detection of Csp; (v) phylogenetic findings on the origin and relatedness of Csp to previously recorded diseases, especially VSD in cacao (Theobroma cacao L.); and (vi) preliminary results and observations from fungicide trials and cultivar screening in Tennessee. The article also outlines research needed to comprehensively understand VSD and accelerate the development of effective management strategies.

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.

"‘Bonnie’s Purple Majesty’: A Cultivar of the Endangered Sunflower Helianthus verticillatus" published on Mar 2025 by American Society for Horticultural Science.