Phytopathology最新文献

Wheat is a critical global food source, yet its production is threatened by stripe rust caused by Puccinia striiformis f. sp. tritici (Pst), which reduces yields by ~5 Mt annually. The resistance gene Yr15, derived from wild emmer wheat, encodes the tandem kinase protein WTK1 and confers wide-spectrum resistance to more than 2,000 Pst isolates. Here, we examined how WTK1-mediated resistance is shaped by pathogen load, isolate identity, and host genetic background, with emphasis on the histopathological dynamics of infection. Susceptible genotypes Kronos S (tetraploid) and Avocet S (hexaploid) showed stable levels of susceptibility across inoculum gradients, whereas their near-isogenic lines carrying WTK1 (Kronos R and Avocet R) exhibited dose-dependent hypersensitive responses, with Avocet R showing slightly stronger reactions. An inoculum of 10 mg/ml consistently distinguished susceptible from resistant responses, providing a reliable threshold for phenotyping. Importantly, WTK1-carrying lines resisted all tested isolates, including the highly virulent Pst#5006. A 336-hour post-inoculation (hpi) time-course revealed that fungal growth diverged between resistant and susceptible plants beginning at 144 hpi. In Kronos R, fungal colonies were detectable up to 96 hpi but were subsequently curtailed by localized programmed cell death. Biomass quantification confirmed no significant increase in fungal load in WTK1 lines from 12-336 hpi. Microscopic analysis further showed that defense activation occurred after haustorium formation, indicating a post-haustorial mechanism of resistance. Together, these findings provide the first detailed temporal map of tandem kinase protein mediated defense in wheat and underscore the robustness of WTK1 across pathogen pressures.

Potato early dying (PED) is a significant concern for potato growers globally. PED is believed to be caused by a combination of soil-borne fungi Verticillium dahliae, V. albo-atrum, Colletotrichum coccodes, Fusarium spp., and the root-lesion nematode Pratylenchus penetrans. However, the causal agents of PED in Alberta have not been thoroughly characterized. We investigated the incidence and abundance of V. dahliae and V. albo-atrum and assessed their relationship with PED severity and yield loss in southern Alberta. Soil samples were collected from 62 potato fields during the falls of 2020 and 2021 and analyzed using quantitative polymerase chain reaction (qPCR) to detect and quantify V. dahliae and V. albo-atrum. For both years, V. dahliae was found in 71% and 45% of the fields, respectively. In contrast, traces of V. albo-atrum were detected in only one field in 2020. Selected fields were surveyed to assess PED severity and yield loss in the summers of 2021 and 2022. The potato fields with high levels of V. dahliae in the soil typically showed more PED symptoms and, in some cases, lower yields. However, some fields with low levels of V. dahliae in soil also showed PED symptoms, indicating that factors in addition to V. dahliae levels in soils are involved in determining PED severity. Colletotrichum coccodes was present in 59% of plant samples collected in 2021 and 41% in 2022. Notably, in 2022, PCR- detectable levels of C. coccodes were apparent earlier than V. dahliae in the growing season.

Four Fusarium oxysporum formae speciales can cause yellows disease of the economically important species in Brassicaceae family. Among these, F. oxysporum f. sp. rapae induces yellows in leaf mustard and Chinese cabbage. SGE1 (SIX gene expression 1) is a transcription factor characterized by the presence of the WOPR box domain. Homologs of SGE1 in other Fusarium species play a crucial role in virulence and regulate the expression of SIX (secreted-in-xylem) effector genes. However, the role of the SGE1 homolog in F. oxysporum f. sp. rapae (FoRP-SGE1) in pathogenesis and fungal development remains unexplored. To investigate its function in regulating pathogenicity and fungal development, gene knockout mutants of FoRP-SGE1 (ΔFoRP-SGE1) were generated and validated. ΔFoRP-SGE1 showed a reduction in conidiation, but normal colony growth and conidial germination. Notably, ΔFoRP-SGE1 completely lost pathogenicity, but it retained the ability to colonize leaf mustard plants, indicating that FoRP-SGE1 is a key pathogenicity factor. Expression of SIX9 and SIX14 was significantly diminished in ΔFoRP-SGE1. Furthermore, most chlamydospores of ΔFoRP-SGE1 lacked the outermost fibrillose coat. Germination of ΔFoRP-SGE1 chlamydospores was also impaired under various stress conditions, including osmotic stress, drought, UV exposure, and fluazinam toxicity. This study presents, for the first time, the role of a Fusarium SGE1 homolog in the morphology and persistence of chlamydospores. Collectively, our findings suggest that FoRP-SGE1 is a critical pathogenicity factor in the leaf mustard-F. oxysporum f. sp. rapae pathosystem and is involved in the development of the fibrillose coat of chlamydospores and their resistance to environmental stresses.

Beet curly top virus (BCTV) has emerged as a major threat to hemp production in the western United States. Despite this concern, little is known about BCTV biology in hemp. This study investigated the incidence and genetic variability of BCTV strains, its impact on cannabinoid profiles, potential for seed transmission, and vector survival on hemp. Field surveys across five states revealed four distinct BCTV strains, with BCTV-CO and BCTV-Wor being the most prevalent. In addition, BCTV-PeCT was detected for the first time in hemp samples from Oregon, Colorado, and New Mexico, while BCTV-PeYD was detected exclusively in New Mexico. Genetic analysis showed high nucleotide diversity and widespread recombination among hemp-associated BCTV strains, consistent with active genetic exchange in BCTV. Furthermore, BCTV was detected in surface-disinfected seeds (77% in Elite genotype, 18% in 791 genotype), and in a small number of seedlings in grow-out experiments (0.98% in Elite, 0.87% in 791). Additional seed dissection experiments in Elite, revealed BCTV presence in 41% of embryos, 72% of endosperm, and 5% of seed coats, demonstrating potential for seed transmission in hemp rather than surface contamination. BCTV infection reduced cannabinoid levels in one hemp genotype but not in another, indicating genotype-specific effects of BCTV on cannabinoid production. Finally, beet leafhoppers, the exclusive vector of BCTV, were unable to survive on hemp beyond seven days indicating that the insect cannot complete its lifecycle on hemp. These findings provide a foundational understanding of BCTV evolutionary dynamics and host interactions in hemp, with implications for disease management.

In this study, we used coniferous and non-coniferous hosts to assess pathogenicity of a Fusarium annulatum isolate derived from southwestern white pine (Pinus strobiformis), along with F. commune isolates derived from coniferous and herbaceous, non-conifer hosts. All isolates of both Fusarium spp. were found to be pathogenic to conifer hosts. For the tested non-coniferous hosts, F. commune isolates were found pathogenic to both rice and tomato, while F. annulatum was only found pathogenic to rice. To investigate the molecular basis of pathogenicity, we identified differentially expressed pathogenicity-/virulence-associated genes by inoculating loblolly pine (P. taeda) seedlings with isolates of conifer-derived F. commune (collected from ponderosa pine [P. ponderosa]) and F. annulatum (collected from southwestern white pine), which were all previously confirmed pathogenic to loblolly pine in our assays. Seedlings were harvested at 12-, 24-, and 48-hours post-inoculation for transcriptomic analyses to identify pathogen genes associated with early infection of the host. Among the upregulated in planta (UIP) genes, we identified putative pathogenicity-/virulence-associated genes including secreted effectors, secondary metabolite gene clusters involved in mycotoxin biosynthesis, and carbohydrate-active enzymes. To identify putative conifer pathogenicity profiles of these potential conifer pathogens, we compared these UIP genes with the predicted proteomes of 17 conifer-associated Fusarium spp. isolates. While these putative pathogenicity profiles did not definitively correspond with pathogenicity on coniferous versus herbaceous hosts, but rather aligned with Fusarium species complexes. A subset of these shared UIP genes may aid in the development of detection methods for conifer-specific pathogens based on Fusarium species complexes.

Infection by aphid-transmitted poleroviruses modulates gene expression associated with plant development and defense. This study assessed the gene expression patterns following cotton leafroll dwarf virus (CLRDV) infection in primary and alternate hosts. Two comparisons (CLRDV-infected vs. non-infested and mock-inoculated vs. non-infested) were evaluated to identify differentially expressed genes (DEGs), and to tease out differences in gene expression profiles between aphid feeding and aphid-mediated CLRDV infection in each host. CLRDV infection was characterized by 2079, 1238, 1484, and 1773 DEGs in the primary host cotton, and in alternate hosts hibiscus, okra, and prickly sida, respectively. The number of DEGs upon aphid feeding was less than CLRDV infection in all hosts except okra. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) terms identified DEGs associated with development, defense, and vector fitness influencing compounds (VFICs) in CLRDV-infected plants. Genes associated with phytohormones, photosynthesis, salicylic acid, jasmonic acid, pathogenesis related proteins, heat shock proteins, transcription factors, membrane transporters, terpenoids, carbohydrates, and amino acids were differentially expressed in CLRDV-infected plants and varied between hosts. Few overlapping and numerous unique genes in the above-stated categories were differentially expressed upon aphid feeding and varied between hosts. DEGs associated with signaling pathways, transcription factors, systemic resistance, pathogenesis related proteins, and carbohydrate and amino acid biosynthesis were common between aphid-mediated CLRDV infection and aphid feeding alone. The observed gene expression patterns reiterate that differences in host susceptibility to the virus and/or the vector could differentially influence host defense and development, and vector fitness.

Sweet cherry (Prunus avium L.) is a commercially vital fruit crop in China. The hop stunt viroid (HSVd) infection in sweet cherry causes dappled fruit. This study investigated the mechanism of dappled fruit formation in HSVd-infected sweet cherry using integrated metabolomics and transcriptomics. Dappled and non-dappled peel tissues were sampled at the color change and ripening stages. UPLC-MS/MS identified 181 flavonoid metabolites, with peonidin-3-O-rutinoside, cyanidin-3-O-glucoside, peonidin-3-O-glucoside, cyanidin-3-O-arabinoside, cyanidin 3-xyloside and cinchonain Ic being significantly enriched in dappled areas. RNA-seq revealed 3,287 differentially expressed genes, with PaCHS, PaCHI, PaDFR, and PaANS up-regulated in dappled areas at the early stage, correlating with anthocyanin accumulation. KEGG enrichment highlighted anthocyanin and flavonoid biosynthesis pathways as central to pigmentation. This study suggests that HSVd disrupts anthocyanin biosynthesis to induce dappled pigmentation, offering novel insights into viroid-host interactions affecting fruit color in sweet cherry.

The spread of Phytophthora ramorum, the causal agent of Sudden Oak Death and Sudden Larch Death, has resulted in a destructive loss of trees, woody shrubs, and ornamentals in nurseries and forests in the US, Canada, and Europe since the late 1990s. Twelve lineages of P. ramorum are described that vary in global distribution and virulence. Herein, we present a maximum likelihood phylogeny for P. ramorum inferred using IQ-TREE and Tree-Based Alignment Selector Toolkit (T-BAS). The phylogeny was generated based on six loci (avh120, avh121, btub, gweuk.30.30.1, hsp90, and trp1). This phylogeny of P. ramorum improves on previous phylogenies since it is dynamic and interactive and incorporates a diverse set of all known global lineages from the US, Europe (NA1, NA2, EU1, and EU2), and ancestral lineages from the putative native range in East Asia. The phylogenetic relationships inferred in the T-BAS tree support lineages NP1 and NP2 of P. ramorum as ancestral to NA1 and NA2 lineages found in North America. In addition, East Asian IC1, IC2, IC3, and IC4 lineages are ancestral to EU1 and EU2 lineages found in Europe. We used sequence data generated from isolates of P. ramorum collected from Ireland and Northern Ireland and placed them accurately in the tree. The P. ramorum phylogeny is available through T-BAS within the DeCIFR platform. This "interactive phylogeny" can be used by the research community to rapidly update and better reflect the evolutionary relationships of new lineages of P. ramorum.

Sclerotinia sclerotiorum causes Sclerotinia stem rot, or white mold, on multiple economically important crops in Michigan. Soybean farmers and crop consultants in the Midwestern U.S. currently use S. sclerotiorum apothecia prediction models to inform fungicide application timing to optimize disease control and economic return. However, current models have not been validated for use in dry bean or potato and do not account for the effects of irrigation on apothecia development. To improve S. sclerotiorum apothecia prediction, on-site weather data were collected and used to generate new binomial logistic regression (LR) and supervised machine learning (ML) models for irrigated soybean, dry bean and potato fields. The ML algorithms investigated included decision trees, random forests and support vectors machines. Decision tree classification models outperformed LR and other ML models, achieving 77% accuracy on testing data. Accuracy increased to 89% when on-site weather data were included, indicating that on-site weather monitoring may be required to reliably predict apothecia presence in irrigated environments. Feature importance analysis identified row shading (the distance the plant canopy extends into the row) as critical for prediction accuracy. The minimum row shading required to trigger apothecia development varied slightly between crop types and row spacings, from 0.15 to 0.21m. Apothecia density peaked when soil temperatures were 21.51°C and volumetric water content were 11.43% and 19.58%. Additionally, a rapid increase in apothecia presence was observed after canopy closure reached 87%. Future model testing and validation will be required prior to deployment as a decision aid for farmers and crop consultants.

Citrus canker, caused by Xanthomonas citri pv. citri, is one of the most devastating bacterial diseases of citrus species. The global population of Xanthomonas citri pv. citri includes three lineages designated as pathotypes A, A* and A^w. While pathotype A is the most prevalent lineage around the world, the citrus canker pathogen in Iran includes only pathotype A* strains. Previous work on the Xanthomonas citri pv. citri strains collected before 2013 showed that two lineages of the pathogen presented in Iran, i.e., 4.1 and 4.4, with 4.4 not present anywhere else at that time. In this study, using a new set of strains collected in 2021-2022, we re-assessed the population structure of the pathogen in Iran using a phylogeographic approach. All strains isolated in Iran still belonged to pathotype A*. Multilocus variable number tandem repeat analysis (MLVA) revealed that 62 Iranian strains collected between 1991-2022 were distributed among 22 haplotypes. Four new haplotypes were identified within the strains isolated in this study which have not previously been reported elsewhere in the world. Although all pre-2013 strains isolated in Sistan-Baluchestan Province of Iran were grouped in subcluster 4.4, all post-2020 strains isolated in the same area were identified as members of subcluster 4.1. None of the post-2020 strains isolated in Iran belonged to subcluster 4.4, which suggests a shift in population structure of the pathogen over the past two decades. Our data would pave the way of research on the population structure of citrus canker pathogen in the area.