Phytopathology最新文献

Tomato spotted wilt virus (TSWV) is a globally important pathogen of peanut, characterized by rapid evolution, broad host range, and capacity to overcome resistance. In this study, we performed deep sequencing of TSWV isolates from two peanut cultivars (GA-06G and Bailey II) and two induced allotetraploids derived from four wild Arachis species ([A. gregoryi × A. stenosperma]^4x and [A. vallsii × A. williamsii]^4x) grown in Georgia, United States. Complete genomes of TSWV and co-infecting peanut mottle virus (PMV) were assembled for all samples. Despite the phylogenetic distance among hosts, TSWV isolates showed high sequence identity and clustered tightly, suggesting limited host-driven divergence. However, segment-wise analysis revealed differential variation: conserved regions included RdRp, G_N/G_C, and N proteins, whereas NSm and NSs-linked to host adaptation and immune suppression-were more variable. This inference is based solely on the TSWV isolates used in this study. Phylogenetic comparison with 113 global isolates confirmed that clustering was driven more by geography than host, with southeastern U.S. isolates forming a distinct clade. Notably, peanut-associated TSWV isolates showed the highest nucleotide diversity among hosts, illustrating their potential to generate resistance-breaking variants. PMV, once thought nearly absent, was detected in all samples, raising new questions about low-level persistence or resurgence. This study reports the first full-genome sequences of TSWV and PMV from U.S. peanuts, including wild-derived genotypes, and highlights the need for sustained genomic surveillance. The results have direct implications for resistance breeding and disease management, particularly as wild genetic resources are increasingly integrated into peanut improvement. [Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Field performance of winter wheat genotypes with quantitative resistance to Stagonospora nodorum blotch (SNB) is influenced by genotype-by-environment interactions (GEIs). This phenomenon explains why cultivars may perform inconsistently across environments, affecting decisions on locally adapted genotypes. Further, GEIs can also affect risk assessment when cultivar disease reaction is used as a model predictor under the assumption of stable responses across environments. Thus, this study investigated GEI effects on four disease metrics: final disease severity (SEV), relative area under disease progress stairs (rAUDPS), time to 50% disease incidence (T₅₀), and the apparent rate of disease increase (ω), describing SNB epidemics of 18 commercial soft red winter wheat cultivars planted in 18 environments in North Carolina from 2021 to 2024. Linear mixed models with various variance-covariance structures for random effects were used to analyze the disease data, and a third-order factor analytic model provided the best fit to the data across the metrics examined. Type B genetic correlation ([Formula: see text]), broad-sense heritability ([Formula: see text]), overall cultivar performance (OP), and global stability (expressed as root mean square deviation [RMSD]) were estimated using model outputs and the factor analytic selection tool method. For SEV, rAUDPS, and T₅₀, values of [Formula: see text] ranged from -0.15 to 0.99, with most environment pairs exhibiting high [Formula: see text] values, indicating an agreement in cultivar rankings, although some low [Formula: see text] values revealed rank instability and non-crossover GEI. Based on OP and RMSD, 'USG 3230' was the top-performing and most stable cultivar, whereas 'TURBO' and 'SH7200' were more unstable cultivars. Cultivar reaction classes derived from OP exhibited consistent class-level means of marginal predictions across environments with varying GEIs, supporting their utility as indicators of SNB susceptibility in risk assessment models. However, the presence of minor non-crossover GEI effects suggests that incorporating environmental drivers of GEI into SNB risk models could enhance prediction accuracy.

Xanthomonas arboricola pv. pruni (Xap) is a well-known phytopathogenic bacterium responsible for bacterial spot in Prunus species. Although cherry has historically been listed as a potential host for this pathogen, the occurrence of Xap bacterial spot in cherry is rare. In the present study, two bacterial strains isolated from cherry in Montenegro and initially identified as Xap were subjected to genomic and pathogenicity analyses. The results showed substantial genetic divergence, along with distinct phenotypic profiles, between these strains and reference Xap strains known to be pathogenic in Prunus. These findings are consistent with recent studies reporting the existence of nonpathogenic, less virulent, or atypical strains of X. arboricola that had previously been misidentified as Xap due to limitations of previous diagnostic methods. The results, together with the historically low number of verified Xap infections in cherry and evidence that some strains may have been misidentified or confused with nonpathogenic or misclassified strains, contribute to the hypothesis that cherry may not be a highly relevant natural host for Xap and should therefore be reevaluated. This could have implications for monitoring strategies, risk assessment, and regulatory measures concerning Xanthomonas management in cherry cultivation. [Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Production of broccoli (Brassica olearaceae L. var. italica), and other cruciferous vegetables (Brassica spp.), has expanded throughout the United States. As a result, associated diseases have become more important in new locations. Alternaria brassicicola, the primary causal agent of Alternaria leaf blight and head rot of brassicas (ABHR), is a major pathogen ubiquitous in all brassica production operations. To better understand how A. brassicicola has adapted to new regions, we developed novel microsatellite primers and identified five polymorphic loci subsequently applied to characterize the population structure and reproductive strategies of field populations from Connecticut, Massachusetts, Virginia, Georgia, and Minnesota. Mating type idiomorphs were also identified 61:189 (MAT1-1:MAT1-2), skewed toward MAT1-2. A total of 250 isolates were collected from nine broccoli fields from five states, and from one field each of cabbage (B. olearaceae L. var. capitata) and brussels sprouts (B. olearaceae L. var. gemmifera) in Minnesota. A relatively large amount of genetic diversity was identified within each field, though population structure was only apparent regionally within MAT1-2 isolates. Using a chi-square analysis, two Minnesota fields met the 1:1 ratio expected for sexually recombined populations. Five fields predominated by a single mating type (MAT1-2) also had non-significant linkage disequilibrium, which is unexpected and could be the result of a parasexual cycle that recombines genotypes without carpogenic sexual outcrossing between mating types. Overall, our results provide valuable insight into the population structure and reproductive strategies of A. brassicicola, specifically the structure and potential parasexual populations of MAT1-2 isolates within fields.

The MYB transcription factor family is one of the largest gene families in plants and plays critical roles in how plants respond to biotic and abiotic stresses. However, the functions of MYB members in high-temperature seedling plant (HTSP) resistance in wheat to Puccinia striiformis f. sp. tritici (Pst) are not well understood. Previously, TaMYB73, an MYB transcription factor, was identified through an RNA-sequencing study of the wheat cultivar Xiaoyan 6 under infection by Pst. In this work, we characterized the molecular function of TaMYB73. The expression TaMYB73 was upregulated following Pst inoculation and high-temperature treatment. Silencing TaMYB73 resulted in an increased number and size of uredinia, a downregulation of salicylic acid (SA)-responsive genes TaPR1 and TaPR2, and a compromised HTSP resistance to Pst. Conversely, transient overexpression of TaMYB73 in wheat enhanced resistance to Pst by reducing fungal biomass and upregulating TaPR1 and TaPR2. The induction of TaMYB73 by SA and its regulation of SA-responsive genes suggest that it may play a role in the SA signaling pathway. Subcellular localization assays confirmed that TaMYB73 is located in the nucleus. Furthermore, yeast two-hybrid, bimolecular fluorescence complementation, and luciferase complementation assays demonstrated that TaMYB73 can form homodimers. Taken together, our findings establish TaMYB73 as a positive regulator of HTSP resistance in wheat. This work provides important insights into the molecular mechanisms of wheat HTSP resistance to Pst and offers strategies for improving wheat's resistance to this pathogen.

Understanding the early invasion and migration mechanisms of the pine wood nematode (PWN, Bursaphelenchus xylophilus) is crucial for disease control, but the dynamics immediately following inoculation remain unclear. Using histopathological observation (via paraffin sectioning and microscopy) in conjunction with a modified Baermann funnel technique, we investigated the initial stages of PWN invasion and migration across different stem types and wound types to delineate the precise migratory pathways. Results showed that cortical resin canals served as the sole pathway for initial PWN invasion; even low inoculation levels (10 to 100 nematodes) enabled PWN invasion through these canals within 1 h post-inoculation (hpi). Optimal migration occurred in the bark of 2-year-old branches, reaching 15 cm (upward)/18 cm (downward) with approximately 11.7% of the inoculated nematodes by 12 hpi. Migration did not differ between natural beetle-feeding wounds and artificial wounds within 12 hpi. Migration through xylem was severely limited (only 3 to 15 nematodes migrating 1-6 cm within 12 h), yet was notably accelerated when passing through branch cross-sections (17 cm in bark and 16 cm in xylem within 6 hpi) compared to the maximum distance (8 cm) observed in beetle-feeding wounds or artificial wounds. Furthermore, a critical invasion window was identified: wound exposure for ≤ 12 h permitted PWN invasion, while exposures of 16 h or 24 h significantly reduced or completely prevented invasion. These results define the first 12 h post-wounding as the key vulnerability period for PWN infection, providing a critical timeframe for targeted prevention of pine wilt disease.

The aggressiveness of seventeen X. fastidiosa strains, representing different subspecies and sequence types (STs), was studied in the surrogated host N. benthamiana by the analysis of the population levels and symptoms dynamics, dose-response relationships and the transcriptomic response of the plant. Colonization of all strains was observed after 7 days post inoculation (dpi), and the first symptoms appeared after 14 dpi. Differences in patterns of population dynamics and symptoms development were observed between strains and there was neither a relationship between population growth and symptoms severity, nor between strains of the same subspecies and STs. Strains IVIA 5387, DeDonno, CN28 and GP18 showed a typical S-shaped dose-effect curve, and the minimum infective dose in N. benthamiana was established at 300 UFC/plant for all strains. The plant response to the infection by the subsp. pauca ST53 strains DeDonno, CN28 and GP18 was studied in relation to the expression of defense genes. A strain-dependent modulation depending on time was observed, where CN28 infection showed the highest gene overexpression (12 out of 19 genes), and DeDonno the lowest (8 of 19 genes). At 4 dpi, all strains upregulated the genes PR1, PR1a and ERF1 and downregulated the PDF1.2 gene, while at 30 dpi most of the genes were downregulated, especially the pathogenesis related (PR) genes, suggesting an immune evasion by the pathogen. Our findings are expected to provide valuable insights into the interaction between X. fastidiosa and its hosts, highlighting the importance of considering differences in aggressiveness among strains and in plant response.

The wheat leaf spot complex is a globally pervasive foliar disease caused by multiple fungal pathogens: Pyrenophora tritici-repentis (tan spot), Parastagonospora nodorum and Parastagonospora pseudonodorum (septoria nodorum blotch), Zymoseptoria tritici (septoria tritici blotch), and Bipolaris sorokiniana (spot blotch). Diagnostic challenges arise from overlapping symptoms and similar morphologies. We evaluated previously released molecular diagnostic tools and found that they either lacked specificity or failed to detect all species in the complex. Existing methods target different multicopy genomic regions and lacks validation against other wheat-associated pathogens. To overcome these limitations, we developed a detection tool targeting a single copy, conserved gene (β-tubulin 1, tub1) across all species. Species-specific primers were designed for multiplex PCR (mPCR) and TaqMan-based real-time quantitative PCR (qPCR), enabling sensitive, specific, and simultaneous quantification. The qPCR accurately quantified pathogen biomass with detection limits down to 0.04 pg of fungal DNA. We further showed that assays were highly accurate and species-specific when tested on wheat tissues inoculated under controlled conditions with defined single-species or mixed infections, as well as on naturally infected samples. PCR-restriction fragment length polymorphism (PCR-RFLP) analysis with selected restriction enzymes further distinguished species with unique cleavage patterns, providing an easy to use and clear identification system. Moreover, we confirmed that the assays do not cross detect barley-associated species such as the barley leaf spot pathogen Pyrenophora teres, ensuring robustness for use where host overlaps occurs. This comprehensive diagnostic provides a rapid and reliable detection, quantification of these pathogens, supporting improved disease diagnosis and enhance breeding for resistance.

Plant viruses that cause minimal to no disease symptoms may not support readily detectable virus levels. Such viruses are of concern when they persist in plant germplasm collections or in breeding populations because they can provide inoculum that can be spread and potentially cause outbreaks in susceptible plant species. The mealybug-transmitted cacao mild mosaic virus (CaMMV) causes symptomatic and asymptomatic infection of cacao trees that vary seasonally. The virus accumulates to low levels in leaves and petioles in leaves of at least some cacao genetic groups, which has confounded reliable CaMMV detection. Here, a multiplex recombinase polymerase amplification (RPA) assay was developed to increase the reliability of CaMMV detection. Three RPA primers were designed to amplify two regions of the movement protein gene (mp) of CaMMV, yielding fragments of 362 and 284 base pairs (bp). To increase detection sensitivity and specificity of CaMMV, two guide RNAs (20 bp) targeting both the CaMMV RPA amplicons were designed to activate Cas12a-mediated collateral cleavage of a fluorescent reporter. An RPA detection efficiency of 100% was achieved with respect to six known CaMMV mp variants, while the analytical sensitivity ranged from ~3 to 40 detectable CaMMV genomes. No signal was observed when cloned cacao-infecting badnavirus sequences or virus-free cacao were used as template, indicating that this assay is highly-specific for CaMMV.

Stemphylium leaf blight (SLB), caused by the fungus Stemphylium vesicarium, is a devastating foliar disease affecting onions in New York state. Primary inoculum sources for SLB epidemics potentially include infected transplants used to establish crops and volunteer onions remaining from the previous season, but little is known about their relative contribution to the population biology of S. vesicarium. In this study, 537 S. vesicarium isolates were obtained during 2022 and 2023 from infected transplants and volunteers, as well as symptomatic main crop plants collected during the mid- and late seasons. To evaluate the relative contributions of infected transplants and volunteers to S. vesicarium populations in New York, nine simple sequence repeat markers were used to characterize the genetic diversity and structure of populations by source and year. A total of 399 multilocus genotypes (MLGs) were identified, of which 27 MLGs were shared among two or more source populations and 28 between year populations. Structure analysis showed that populations from transplants were distinct from volunteers and main crop plants collected during the mid- and late seasons with low admixture. Populations had high genotypic diversity and genetic differentiation, also suggesting a minimal contribution of infected transplants to the New York S. vesicarium populations. The dominance of MLGs from volunteers to main crop populations suggests that the elimination of volunteers should be included in integrated disease management strategies. Crop rotation and hygiene practices to remove and destroy volunteer onions after harvest may be key to reducing the primary inoculum for SLB epidemics.