Plant disease最新文献

Camphor tree leaves are a valuable source of essential oils, but their yield is severely threatened by anthracnose caused by Colletotrichum fioriniae and C. siamense. To develop an eco-friendly alternative to chemical pesticides, we isolated a strain of Burkholderia pyrrocinia, designated DLL-114, from camphor tree roots. DLL-114 exhibited strong antagonistic activity against both pathogens, and inoculation assays demonstrated that it significantly reduced lesion areas while maintaining leaf greenness. Moreover, DLL-114 showed broad-spectrum antifungal activity against several crop pathogens, with its antifungal effects mediated by multiple antagonistic pathway. Whole-genome sequencing using Illumina and PacBio platforms revealed an 8.36 Mb genome comprising three circular chromosomes and two plasmids, with a GC content of 66.12%. The genome encodes 7,739 protein-coding genes and 21 secondary metabolite biosynthetic gene clusters, only one of which showed complete similarity to a known cluster. Notably, biosynthesis operons for gluconic acid, pyrrolnitrin, catecholate siderophores, and ornibactin were identified. This genomic features, together with metabomic evidence, suggest that DLL-114 is a promising candidate for the production of bioactive secondary metabolites and a potential biocontrol agent for sustainable agriculture.

Diverse climatic environments lead to distinct ecological conditions in different rice planting regions, resulting in a wide variety of Magnaporthe oryzae (rice blast fungus) populations that frequently adapt and vary to suit their specific ecological niches. Understanding the diversity of M. oryzae populations across different ecological planting zones is fundamental for controlling rice blast disease. This study systematically investigated the population structure, distribution of avirulence (Avr) genes, and pathogenicity of M. oryzae using 174 monosporic isolates collected in 2021 from three counties in Hunan Province: Xinhua, Longhui, and Liuyang. The results indicated that while the number of physiological races in the three locations was similar, the dominant physiological races differed significantly. Overall, the resistance gene Pikm exhibited the highest resistance frequency. Additionally, genes like Pik, Pikp, and Pizt showed good resistance against pathogen populations in some ecological zones. Resistance frequencies varied dramatically across different ecological environments, indicating differing practical value for specific resistance genes in different ecological regions. Representative isolates from each location were screened and used to test the resistance of locally main cultivated varieties. The results revealed significant differences in the proportion of varieties resistant to the pathogen populations from the three locations. These findings provide a data basis for resistance breeding and the rational distribution of rice varieties across different ecological regions in Hunan Province.

Kiwifruit bacterial canker (KBC), caused by Pseudomonas syringae pv. actinidiae (Psa), threatens global kiwifruit production. Traditional control methods face challenges like bacterial resistance and environmental issues. In this study, four lytic phages (pSM43, pGZ41, pWA51, and pSO21) were isolated and characterized using Psa M228 as the host bacterium. Notably, the phage pGZ41 represents a novel phylogenetic lineage, and the four-phage cocktail demonstrates significant advantages over previously reported single phages or mixtures in terms of lytic spectrum and resistance management. These phages exhibit distinct structural features and biological properties. Genomic sequencing classified them as double-stranded DNA viruses with genome sizes spanning 38,130 - 100,813 base pairs (bp), encoding 91 to 309 putative opening frames. The complete genome sequences have been deposited in GenBank under accession numbers PX673947 (pSM43), PX673946 (pGZ41), PX673948 (pWA51), and PX673949 (pSO21). The phage cocktail has a significant inhibitory effect on the growth of Psa M228 in vitro, in Arabidopsis thaliana and kiwifruit leaf discs. In vitro tests demonstrated that phage cocktails could effectively suppress bacterial growth and delay the emergence of resistant strains within a short period. In A. thaliana, phages exhibited strong antibacterial capabilities, reducing bacterial load by 4.92 log CFU/g in the treatment group and 4.33 log CFU/g in the prevention group compared to the infected control group. In kiwifruit leaf discs assays, the prevention group treated with phage cocktails exhibited superior efficacy, reducing lesion areas by 3-5 times compared to the treatment group. The significant efficacy in plant models, combined with the high environmental stability of the phages (particularly pGZ41), underscores the strong potential of this phage cocktail as a practical, sustainable, and environmentally friendly biocontrol agent for integrated management of kiwifruit canker in orchard settings.  This multi-level validation suggests these phages as promising biocontrol agents for controlling kiwifruit canker caused by Psa.

Colletotrichum sublineola Henn. causes anthracnose disease on grain, forage, and sweet sorghum [Sorghum bicolor (L.) Moench], and on the related weed Johnsongrass [S. halepense (L.) Pers.]. Previous genetic fingerprinting studies using neutral markers indicated C. sublineola in the southeastern United States comprises two divergent populations mostly associated with the Sorghum host species. In the current study, we further characterized these populations by evaluating restriction fragment length polymorphisms (RFLPs) in fourteen putative pathogenicity-related genes (twelve small secreted-protein effector genes and two secondary metabolite-associated protein genes), and by sequencing polymorphic regions of a subset of these genes. These analyses identified three clades: one (clade A) corresponded to the previously defined population isolated mostly from S. bicolor; the other two (clades B and C) revealed further subdivision within the population recovered mostly from S. halepense. Evidence for reticulation among the gene trees suggested that the three clades correspond to genetically distinct subpopulations within C. sublineola. In greenhouse pathogenicity assays, representatives of the A clade caused disease only on S. bicolor, while clade B members caused disease only on S. halepense, and isolates belonging to clade C were pathogenic to both host species. Estimates of genetic variation indicated that the B clade was the most diverse. Members of the three subpopulations were morphologically similar but could be differentiated by single-nucleotide polymorphisms (SNPs) within a subset of the pathogenicity gene alleles, and several phylogenetic sequence markers. These SNPS could be used to identify members of the three subpopulations for future diagnostic, breeding, and research purposes.

Rice bakanae disease (RBD), caused by Fusarium fujikuroi, threatens global rice production. While the phenylpyrrole fungicide fludioxonil shows efficacy against F. fujikuroi, resistance mechanisms remain understudied. The current study found that the fludioxonil sensitivity of 101 F. fujikuroi isolates collected in the rice fields of Xinxiang City in the Henan Province of China ranged from 0.025 to 0.759 μg/ml, with an average EC₅₀ value of 0.3441 ± 0.1961 μg/ml (standard error). Four highly fludioxonil-resistant F. fujikuroi laboratory mutants were generated by repeated exposure to fludioxonil, and they exhibited enhanced mycelial growth and sporulation but reduced spore germination, pathogenicity, and osmotic stress tolerance, alongside abnormal hyphae. Molecular analysis identified amino acid substitutions in the target protein Ffos-1, notably at residue 672 (A672P/T). These acid amino changes reduced the minimum binding energy in docking models. Ffos-1 expression was significantly (P < 0.05) upregulated in fludioxonil-resistant F. fujikuroi mutants. Meanwhile, cross-resistance analysis revealed a significant (P = 0.0064) correlation between fludioxonil and iprodione but not epoxiconazole, prothioconazole, or carbendazim. However, field monitoring is critical, as baseline shifts could compromise fludioxonil efficacy. These findings highlight Ffos-1's role in fludioxonil action and resistance, informing integrated strategies to delay resistance spread and improve RBD management.

Xanthomonas hortorum pv. carotae (Xhc) is a plant-pathogenic bacterium that causes bacterial blight of carrot. It impacts international trade due to little to no tolerance for the pathogen in carrot seed. Because the biennial crop has overlapping growing seasons and Xhc has been detected in the air in areas of carrot seed production, an improved understanding of the dispersion pathways is needed. Experiments (Airborne Xanthomonas Experiments- Madras [AXE-M]) conducted in central Oregon were designed to characterize the airborne transport and deposition of particles dispersing Xhc during harvest events. Debris samples were collected with a novel passive sampling device, the Cascade Settling Trap (CST), that sorted particles into size classes of interest as the particles were deposited out of the air column. CSTs were used during one harvest event in 2021 and three in 2022. Negative binomial regression analysis conducted on data collected in 2022 indicated that particle size and the distance from which particles were sampled can be predictive of the amount of Xhc detected. Burkard samplers were utilized in 2021 and 2022 to quantify airborne Xhc during the growing season and specific events of interest. Meteorological data, in conjunction with the use of optical particle counters, allowed for estimation of real-time airborne particle concentrations and their potential for transport. By developing a more detailed understanding of the aerobiology of Xhc, better risk assessment tools and pathogen management strategies can be employed to assess the potential for these particles to disperse Xhc across varying scales.

The Florida sugarcane industry is transitioning from manual to mechanical planting systems, which use comparatively smaller seed cane pieces (billets) as planting material. A major limitation of mechanical planting is the increased seed cane requirement due to mechanical damage and the increased vulnerability of seed cane pieces to soil-borne pathogens that cause sett rots, particularly pineapple disease caused by Thielaviopsis spp. Current sugarcane breeding programs in Florida screen for major diseases such as rusts, smut, ratoon stunting, and viruses early in the breeding process, but not for pineapple disease. This study aimed to isolate and identify Thielaviopsis spp. in the Everglades Agricultural Area (EAA), develop a single-bud inoculation protocol for greenhouse-based disease screening, and phenotype the current widely grown sugarcane varieties in Florida against Thielaviopsis spp. The pathogen was confirmed as T. ethacetica, consistent with previous reports from the EAA. A reproducible inoculation method was established and validated through symptom assessment, pathogen re-isolation, and molecular confirmation. Using this protocol, six widely grown Florida sugarcane varieties showed significantly reduced germination (by more than 50%), as well as reduced above- and below-ground morphological characteristics under infection, indicating susceptibility. Varietal differences were observed, with CP 03-1912 showing the highest mortality percentage and reduced growth under T. ethacetica infection. These findings highlight the vulnerability of current varieties to pineapple disease, especially under mechanical planting systems where smaller seed cane pieces are used. Furthermore, the developed inoculation protocol provides a scalable tool for early-stage evaluation of resistance in breeding programs, offering potential to accelerate the development of varieties better adapted to mechanical planting.

The fungal plant pathogen Ramularia crupinae is the first biological control agent approved for the management of the federally-listed noxious weed Crupina vulgaris (common crupina) in the United States. Widespread common crupina infestations threaten western U.S. rangelands and pastures by decreasing biodiversity and agricultural productivity through the displacement of native and beneficial plant species. This study reports the development of a sensitive and species-specific quantitative PCR (qPCR) diagnostic assay designed for tracking R. crupinae infections and monitoring impact following a field release. A unique group I intron located within the 18S ribosomal RNA region permitted the development of a specific and sensitive diagnostic assay capable of detecting R. crupinae in both symptomatic and asymptomatic common crupina tissue. Species-specificity was validated with no cross-reactivity against the closely related species R. acroptili and 47 common crupina fungal endophyte cultures collected from field samples prior to R. crupinae release. Serially diluted R. crupinae DNA was used to demonstrate a qPCR detection limit of 47 fg. This R. crupinae diagnostic assay is highly accurate and specific, does not require post-amplification visualization, and supports high-throughput processing of field samples, making it well suited for tracking R. crupinae establishment and spread. Monitoring R. crupinae movement is critical for studying the impact and epidemiology of this introduced biological control agent.

Alternaria brassicicola is the causal agent typically associated with Alternaria leaf blight and head rot (ABHR) disease in broccoli and related crops in the Eastern United States. In 2020, a new species, A. japonica, was reported as causing disease in broccoli and other vegetables in this region. We conducted a multistate pathogen survey during the growing seasons of 2022 and 2023 to assess the distribution and occurrence of A. japonica in relation to A. brassicicola in five broccoli-producing states. Our approach specifically targeted collection of broccoli leaves with lesions typical of ABHR within commercially grown fields that were managed using either organic or conventional approaches in Connecticut, Massachusetts, New York, Virginia, and Georgia. Only typical ABHR leaf lesions were selected for pathogen isolation, and subsequently, sequencing of the Alternaria major allergen a1 gene was used to identify Alternaria species. The predominant species isolated was A. brassicicola (88% in 2022 and 94% in 2023), and the second most common was A. alternata (12% in 2022 and 6% in 2023), which was obtained from fields in Connecticut and Massachusetts in 2022 and in Virginia in both years. Alternaria japonica was not found in either year. Symptoms of A. alternata were indistinguishable from A. brassicicola, as were colony morphologies. Although A. alternata is considered a generalist and of little consequence for broccoli, it is considered a pathogen of significance on multiple crops (blueberry, citrus, pistachios), but there remains scant information on the disease etiology on broccoli. Therefore, we inoculated broccoli with A. alternata in controlled conditions to shed light on possible differences in infectivity of these species on broccoli. Results of our study showed that A. alternata is pathogenic on broccoli, capable of initiating infection and causing lesions typical of ABHR. This indicates that future disease surveys of ABHR should conclusively identify the species of Alternaria that are causing disease. Additional research is needed to determine the significance of this finding in relation to yield impacts, epidemiology, fungicide resistance, and management recommendations.

Cranberries are vegetatively propagated, yet the industry lacks standardized treatments or regulations to prevent pathogen transmission through field-sourced propagative material. This study evaluated heat treatments as a potential strategy for mitigating fruit rot fungi survival. A three-part experiment was conducted. First, Colletotrichum fioriniae conidia were tested in vitro for heat tolerance, against 25, 37, 42, 44, 47, and 49°C, showing reduced survival at 44°C and complete mortality at 47°C and 49°C. Second, greenhouse trials assessed cranberry cutting survival following hot water treatments. Field-sourced cuttings of two cultivars ('Stevens' and 'Mullica Queen') were exposed to 37, 42, 44, 47, and 49°C, alongside a non-treated control (25°C). Cuttings remained viable up to 49°C, with no significant differences in survival compared to controls (P = 0.991 and P = 0.365 for 'Stevens' and 'Mullica Queen', respectively). Finally, two trials tested the efficacy of heat treatments on cuttings inoculated with C. fioriniae conidia. Treatments at 47°C and 49°C significantly improved survival for 'Stevens' (P = 0.0081 and P = 0.0045) and 'Mullica Queen' (P = 0.0427 and P = 0.00000021). These results indicate that short-duration hot water treatments can reduce survival of C. fioriniae conidia under controlled conditions while maintaining cranberry cutting viability, supporting further evaluation of heat treatment as a potential sanitation step for cranberry propagation material.