Plant disease最新文献

Strains from the genus of Pectobacterium can cause soft rot in numerous important plants, leading to significant losses. 16S rRNA gene sequences reliably identify genera, but species identification is sometimes challenging due to indistinguishable species or strains and unrecognized new taxa. Therefore, a dependable and straightforward classification method is needed. In this study, we analyzed the complete genome sequence and predicted genome components of Pectobacterium strains. We also assessed their genetic relationships using average nucleotide identity and in silico DNA-DNA hybridization, alongside phylogenetic analysis. This was done by examining the whole-genome sequences of 14 new strains isolated in our laboratory, responsible for plant soft rot, and comparing them with 64 strains' genome sequences available in GenBank. The results reveal that three subspecies of P. carotovorum with genome sequences deposited in GenBank (PccS1, PCC21, and strain 67) need to be reclassified as separate species and also confirm that our new isolated strains are accurately categorized at the species level. Additionally, the virulence and adaptability of certain strains of Pectobacterium (PccS1, SCRI1043, and SCC3193) are influenced by horizontal acquisition genes. Furthermore, our findings suggest that the diversity in the car gene cluster among Pectobacterium strains likely stems from gene losing, as well as the auto-induced regulatory mechanisms underlying virulence determinant gene activation, and Car biosynthesis might act in different ways in PccS1, enhancing our knowledge of their genomic traits through comparative studies.

Xinjiang is a major melon-producing region in China, where viral diseases severely constrain both yield and quality. Despite their importance, the species composition, spatial distribution, and infection dynamics of melon viruses remain incompletely characterized. To address this, we collected 840 symptomatic melon samples from 12 prefectures in Xinjiang and employed RT-PCR with virus-specific primers for detection. Eight viruses were identified: zucchini yellow mosaic virus (ZYMV, 85.5%), watermelon mosaic virus (WMV, 81.2%), cucumber mosaic virus (CMV, 80.1%), cucurbit aphid-borne yellows virus (CABYV, 57.9%), papaya ringspot virus (PRSV, 42.3%), cucumber green mottle mosaic virus (CGMMV, 25.5%), cucurbit chlorotic yellows virus (CCYV, 20.5%), and melon necrotic spot virus (MNSV, 11.1%). Virus composition exhibited pronounced spatial heterogeneity, with southern Xinjiang showing a broader spectrum of viruses and higher diversity of co-occurring infections compared to northern prefectures. Virus Mixed Infections (VMI) were widespread, with CMV, WMV, and ZYMV most frequently involved. Across the dataset, 90 distinct VMI patterns involving 2-8 viruses were documented, and the most common combinations tended to cluster geographically within individual prefectures or across adjacent prefectures. These patterns highlight the complex, region-specific structure of melon viromes and suggest that local climatic conditions, cropping intensity, and host availability drive both virus diversity and mixed-infection dynamics. Overall, this study provides a comprehensive baseline of melon virus occurrence in Xinjiang, emphasizing the spatially structured nature of viral communities and the prevalence of mixed infections. These insights are critical for informing targeted disease management strategies, including region-specific surveillance, vector control, and the development of multi-virus-resistant melon cultivars.

Fusarium head blight (FHB), one of the most economically important diseases on wheat, is primarily managed through the application of chemical fungicides during the heading and flowering stages. To assess the long-term impact of different fungicidal mechanisms on the sensitivity of FHB pathogens, this study evaluated temporal changes in the sensitivity of Fusarium asiaticum to phenamacril (a novel cyanoacrylate fungicide) and tebuconazole (a sterol demethylation inhibitor fungicide). Sensitivity was determined by measuring mycelial growth inhibition in F. asiaticum field populations collected in 2008 (100 strains), 2021 (50 strains), and 2023 (50 strains) from Jiangsu and Anhui provinces of China, where FHB pressure and fungicide usage are high. A significant decline in F. asiaticum sensitivity to phenamacril over 15 years was observed, with EC₅₀ values nearly doubling between 2008 and 2023. In contrast, no notable change in sensitivity to tebuconazole was observed over the same period, indicating its stable inhibitory effect on F. asiaticum. These findings highlight the challenge of F. asiaticum adaptation to phenamacril, posing a significant concern for the long-term management of FHB in wheat cultivation.

Phytophthora root rot (PRR), caused by Phytophthora cinnamomi, is a major production challenge for avocado growers worldwide. PRR management includes cultural practices, the use of resistant rootstocks, and fungicide applications, however, the recent emergence of more virulent and potassium phosphite-resistant pathogen populations has reduced the effectiveness of these management practices. We evaluated the efficacy of Oomycota fungicides to control PRR in five unreleased experimental rootstocks developed by the University of California, Riverside (UCR) and two commercial rootstocks grafted with 'Hass' under greenhouse conditions. All rootstocks were inoculated with P. cinnamomi and treated with either one of six fungicides representing different modes of action to assess PRR management by evaluating PRR incidence, pathogen propagules in soil (ppg), root health, and stem water potential (SWP). All fungicides reduced PRR incidence and pathogen ppg values ranging from 2.1 to 12.3 % and 0.8 to 2.7 ppg, respectively, compared with the untreated control values (36.2% and 11.8 ppg). Potassium phosphite treatments were only effective when using the most resistant rootstocks. Oxathiapiprolin was the best treatment followed by mefenoxam, fluopicolide, ethaboxam, and mandipropamid. The five UCR experimental rootstocks exhibited significantly less PRR incidence (1.8 to 7.4 %) and P. cinnamomi ppg (0.7 to 2.5 ppg) than the susceptible control (28.2% and 8.9 ppg). Improved PRR management was achieved by combining the most resistant rootstock with fungicide treatments, indicating the cumulative effect of rootstock resistance and fungicide treatment. These results support the commercial release of these UCR experimental rootstocks and registration of new Oomycota fungicides to control avocado PRR.

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most significant diseases affecting production in wheat-growing regions of China. Fluxapyroxad and mefentrifluconazole exhibit broad-spectrum activity against a wide range of plant pathogens, including Bgt. This study presents a comprehensive investigation of the efficacy of fluxapyroxad and mefentrifluconazole in controlling wheat powdery mildew in three Chinese provinces. Sensitivity baselines for Bgt isolates against fluxapyroxad (0.9111 μg/ml) and mefentrifluconazole (1.3224 μg/ml) were established. Bgt isolates collected from 2022 to 2024 demonstrated sensitivity or low resistance to fluxapyroxad and sensitivity, low resistance, or moderate resistance to mefentrifluconazole. The results revealed positive cross-resistance between mefentrifluconazole and tebuconazole but not between fluxapyroxad or mefentrifluconazole and other fungicides. For fluxapyroxad, three site mutations were identified within the SDHD subunit, but they did not result in amino acid changes. For mefentrifluconazole, overexpression of QCYP51A and QCYP51B genes was identified as a significant factor contributing to low-level resistance in Bgt. Both fluxapyroxad and mefentrifluconazole, individually and in combination, exhibited high control efficacy (>89%) against wheat powdery mildew. This research provides valuable insights into the current status of Bgt resistance to these fungicides and offers guidance for their judicious application in the field.

Citrus stubborn disease (CSD), caused by Spiroplasma citri, presents a significant risk to citrus production, resulting in considerable yield losses when infections remain undetected. Accurate and timely diagnosis is crucial for effective disease management. However, existing nucleic acid-based methods, such as PCR and qPCR, require laboratory equipment and are not easily applicable in the field. This study developed a CRISPR-Cas12a-based DETECTR (DNA endonuclease-targeted CRISPR trans-reporter) assay for the rapid, sensitive, and specific detection of S. citri, targeting the spiralin gene. An optimized recombinase polymerase amplification (RPA) primer pair and CRISPR-RNA (crRNA) were utilized for sequence-specific activation of Cas12a, enabling cleavage of fluorescent and lateral flow-compatible reporters. The assay demonstrated a detection limit of 1 attomolar (aM) (around 1.8 genome copies) using a fluorescence plate reader and 10 aM using blue-light visualization and lateral flow assay (LFA). Specificity testing revealed discrimination against other phytopathogenic spiroplasmas, including S. kunkelii and S. melliferum. Validation in the plate-reader format with DNA extracted from symptomatic citrus samples showed 100% consistency with qPCR results. A 10-minute NaOH-Tris crude extraction protocol was also assessed, facilitating straightforward and equipment-free sample preparation. Relative to DETECTR assays with kit-extracted samples, crude extracts preserved full diagnostic sensitivity in fluorescence assays and achieved 70% accuracy in LFA and visual formats in a subset of the same samples. These findings establish a dependable, portable, and highly sensitive diagnostic approach for S. citri, providing a practical tool for on-site detection and enhanced management of citrus stubborn disease.

Stem blight and dieback of blueberry caused by Botryosphaeriales species is a significant disease worldwide. In Sinaloa, Mexico, stem blight and dieback symptoms are commonly observed in commercial blueberry fields. Therefore, this study aimed to identify the Botryosphaeriales species responsible for disease symptoms in blueberry plants in Sinaloa, Mexico, through a combination of phylogenetic, morphological, and pathogenic approaches. For this, symptomatic samples were collected from plants in 15 commercial fields located in the municipalities of Culiacán, Navolato, El Fuerte, Ahome, and Guasave in the state of Sinaloa, Mexico. Fungal isolations were carried out from the symptomatic tissues, and 105 isolates with typical characteristics of Botryosphaeriales members were purified and preserved. A total of 24 isolates were selected for morphological, phylogenetic (ITS, tef1-α, and tub2), and pathogenic analyses. The phylogenetic inference revealed six species of the Botryosphaeriaceae family, Lasiodiplodia brasiliense, L. subglobosa, L. theobromae, Neofusicoccum brasiliense, N. kwambonambiense, and Cophinforma tumefaciens, as well as Pseudofusicoccum stromaticum, which belongs to the Pseudofusicoccaceae family. In the pathogenicity test, all the isolates induced stem blight symptoms on blueberry branches inoculated with mycelial plugs. Lasiodiplodia spp. isolates were the most aggressive, followed by P. stromaticum, C. tumefaciens, and Neofusicoccum spp. Furthermore, the aggressiveness among the isolates of the different species was significantly different. This study represents the first association of the genera Cophinforma and Pseudofusicoccum, as well as the species L. brasiliense, L. subglobosa, and N. brasiliense, causing stem blight and dieback of blueberry worldwide and provides a basis for initiating research on the integrated management of this complex disease in Sinaloa, Mexico.

Puccinia striiformis f. sp. tritici (Pst) is a destructive pathogen renowned for its dual reproductive modes, an asexual stage on wheat and a sexual stage on barberry (Berberis), which makes wheat cultivars vulnerable to newly emerging races. However, little has been known about the impact of treatment on barberry plants on declining population genetic diversity and race composition. In this study, we selected six barberry-wheat coexisting sites in which Pst occurs sexually as treatment and control groups for experimental purposes. The treatment group was treated with triadimefon fungicides on barberry at the early pycnial stage to suppress sexual reproduction. Conversely, the control group represented sexual reproduction without fungicide application. Pst populations from wheat fields close to barberry with and without fungicide treatment were phenotyped on Chinese differentials and genotyped using a DNA microarray. The results showed the treatment population displayed a lower heterozygosity level (F_hom = -0.36945, Tajima's D = 0.285033) and a lower genetic diversity (π = 0.000156053) compared with the control population (F_hom = -0.41745, Tajima's D = 0.955451, π = 0.000184483), and a significant difference was observed between both populations (P < 0.001; P < 0.05). The treatment population identified 17 new races and 3 known races, and the control population identified 46 new races and 8 known races. The treatment population (α = 4.644) showed a lower diversity of the standard races than that of the control population (α = 5.194) based on a set of 25 Yr-single gene lines. Our results showed the significant impact of fungicide application on barberry to minimize the emergence of new races and the level of genetic diversity. This study provides guidance to growers, emphasizing the importance of timely fungicide application on barberry to ensure the long-term resistance durability of wheat cultivars against stripe rust.

Vascular streak dieback (VSD) poses a significant threat to the sustainability of woody ornamentals in the United States, particularly Cercis spp. (redbud). This study aimed to develop reliable molecular diagnostic tools for detecting Ceratobasidium sp. D.P. Rogers (Csp), the fungus consistently detected from VSD-symptomatic redbuds and other woody ornamentals. Molecular markers can provide rapid and accurate detection for fastidious fungi such as Csp that are challenging to recover in culture media. However, current molecular tools for Csp detection lack sensitivity and specificity. To address this, specific PCR and quantitative PCR (qPCR) primers were developed, targeting the internal transcribed spacer (ITS) genetic region. The existing primers for the second-largest subunit of RNA polymerase II (RPB2), translation elongation factor 1-alpha (TEF1-α), and ATP synthase subunit 6 (ATP6) genetic regions of Rhizoctonia fungi were also redesigned to enhance the sensitivity and accuracy of detection for Csp. The CP-qP-Csp primer set, with a detection limit of 86.02 pg/μl, effectively detected Csp in VSD-symptomatic tissues, cultures, and soils and is recommended for molecular detection of Csp from woody ornamentals in the U.S. Cross-platform validation across seven laboratories confirmed the robustness of the assays. These findings provide nursery producers with critical early-detection capabilities, potentially preventing significant economic losses and contributing to the sustainability of woody ornamental production. Future research will focus on refining these assays for field applications and exploring the genetic characteristics of Csp across different hosts and pathogen interactions to better understand the epidemiology of VSD.

Vascular streak dieback (VSD) is a serious new threat to woody ornamental plant production in the United States. From April to November of 2022, 2023, and 2024, a survey was conducted by the Virginia Department of Agriculture and Consumer Services to determine the distribution and impact of a fastidious Ceratobasidium sp. D.P. Rogers (Csp) fungus associated with VSD of woody ornamental plants in production nurseries in Virginia. Csp was detected using PCR and quantitative PCR from 285 of 997 plants tested (28.6%), representing 44 broadleaf and 2 coniferous host genera from 53 nurseries and 8 landscape sites across 37 municipalities. In a phylogenetic analysis based on internal transcribed spacer, large ribosomal subunit, rpb2, tef1-α, and atp6 sequences, the Virginia isolates were identical to isolates from Tennessee and strongly supported as a distinct species from Ceratobasidium theobromae. The robustness of the species-specific CP-qP-Csp and Than-ITS1/2 PCR primer sets used to detect Csp was also compared with detection limits of 186 and 1,164 fg/μl of Csp DNA, respectively. For sequencing, the basidiomycete-specific ITS1-F/4-B primer set was able to target Csp from xylem tissue from 52% of 50 samples tested, although the universal fungal ITS1/4 set failed to target Csp from xylem tissue. Questions regarding the detection, associated symptoms, and impact of this putative pathogen in Virginia are discussed.