Phytopathology最新文献

Xylella fastidiosa is a plant-pathogenic bacterium native to the Americas. It has a wide host range and causes significant diseases in economically important crops, including grapevines, citrus, and olive trees. Since 2013, this bacterium has been detected in Europe and other countries of the Mediterranean basin, leading to the identification of several subspecies (multiplex, fastidiosa and pauca) and sequence types (STs) in various plant species in Italy, France, the Balearic Islands and mainland Spain, Portugal, Israel and Lebanon. This study focuses on genomic analyses of the subspecies pauca ST53 strains detected in France. ST53 was identified (i) on intercepted coffee plants in the Pays-de-la-Loire region in 2014 and 2015, and (ii) on two infected host plants collected in Menton in the Provence-Alpes-Côte d'Azur region in 2015 and 2019. As an efficient and promising alternative to cell culture, the targeted enrichment method developed specifically to capture X. fastidiosa gDNA was applied to obtain the whole genome. Phylogenetic and genomic comparisons were carried out to compare the ST53 genomic sequences of the samples from France with a range of X. fastidiosa subspecies pauca genomic sequences from public databases, including ST53 from Italy and Costa Rica. The results obtained from these different approaches revealed close genetic relatedness between the strains. A tip-dating analysis and transmission tree were performed, supporting the hypothesis that some ST53 strains from France may be related to the same introduction event than the Italian strains.

Mycotoxin contamination of wheat and corn grain from Fusaria is a major agricultural concern. To characterize the population of Fusarium in Michigan, 569 isolates were collected, and species composition, TRI genotype, in vitro fungicide sensitivity, and fungicide field efficacy were determined. In wheat, the Fusarium sambucinum species complex comprised 90% of isolates, of which 82.5% of all isolates were F. graminearum. In corn, the F. sambucinum species complex comprised 40%, with 37% identified as F. graminearum, whereas species from the F. fujikuroi species complex comprised 50%. Within the F. fujikuroi complex, F. awaxy (4.6%) was found and had not previously been identified in the United States. Across F. graminearum isolates, TRI genotypes were found at the following percentages: 92% 15-acetyldeoxynivalenol (15-ADON), 6% 3-ADON, 1.6% NX-2, and no NIV. In vitro mycelial growth sensitivity assays to triazole fungicides demonstrated that Fusaria were more sensitive to metconazole than to tebuconazole or prothioconazole. Species-specific differences in sensitivity were identified across the fungicides tested, with F. tricinctum species complex members significantly less sensitive than F. graminearum isolates, and the F. fujikuroi species complex was significantly more sensitive. Within F. graminearum, 10 isolates had median effective concentration (EC₅₀) values 10-fold greater than sensitive isolates. A subset of these F. graminearum isolates were chosen to investigate if reduced sensitivity in vitro would lead to practical resistance in vivo. Field plots were inoculated with spore suspensions; however, no differences in the relative fungicide efficacy were found, signaling that no demethylation inhibitor fungicide resistance was identified in our collected isolates, despite differences in vitro. Although currently, there may not be practical resistance, monitoring should continue, as there is variation in in vitro sensitivities present within and among species.

Wheat yellow mosaic virus (WYMV) is the main cause of wheat yellow mosaic disease. Although its regulation of protein translation and interactions with host proteins are well studied, independent regulation of the virus genome is poorly understood. This study performed in vitro experiments investigating replication regulation by the 5' and 3' untranslated regions of WYMV RNA2. The results confirm that the RNA-dependent RNA polymerase (nuclear inclusion protein b [NIb]) can only recognize and catalyze the synthesis of 3' 190-nt complementary chains in vitro. RNA structure probing and mutation analysis identified ³⁵⁹⁷AUU and ³⁶⁰⁷GGCU as novel interaction sites of NIb; both are essential for maintaining normal replication. Our findings provide an empirical basis for in vivo experiments on regulation of WYMV genome replication and provide a theoretical basis for the prevention and control of WYMV-related crop diseases.

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.

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.

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.