Plant disease最新文献

Early leaf spot (ELS), caused by Passalora arachidicola, is the most prevalent and yield-limiting foliar disease affecting peanuts in Oklahoma. Quantifying yield losses associated with end-of-season defoliation caused by ELS is essential for evaluating the effectiveness of currently deployed control strategies. To that end, a meta-analysis was conducted to assess the heterogeneity in the relationship between ELS defoliation (percentage) and peanut yield (kilograms/hectare) of Spanish cultivars (Arachis hypogaea ssp. fastigiata var. vulgaris) in Oklahoma. Data were mined from fungicide efficacy trials performed in small plots across Oklahoma between 1990 and 2023. Studies (n = 49) over 26 years met the criteria of at least a 10% difference between the minimum and maximum defoliation within the study. A random coefficient model was successfully fitted to the data using maximum likelihood. The estimates of population average of the intercept and slope were [Formula: see text] = 4,296.6 kg/ha (SE = 131.9) and [Formula: see text] = 13.7 kg/ha (SE = 0.9), respectively. The damage coefficient, which represents the percentage reduction in yield per percentage point increase in crop defoliation, was 0.32%. These results allow the prediction of yield loss given for end-of-season defoliation levels and guide peanut producers and researchers in Oklahoma regarding modifying production practices and developing decision-making tools to mitigate losses resulting from ELS defoliation.

Southern corn rust, caused by Puccinia polysora Underw., is a worldwide maize disease. With the changes in global climate and farming systems, southern corn rust has become one of the major diseases that seriously threaten the safety of maize production in China. The disease is airborne and presents regional epidemic characteristics in China; however, its population structure in different regions is still unclear. In this study, we used high-throughput sequencing techniques with a genotyping-by-sequencing approach to study the population structure of P. polysora in the pathogen's winter-reproductive regions. Population genetic analysis indicated that the P. polysora isolates from Ledong, Hainan, collected in July formed a distinct genetic group, indicating seasonal genetic differentiation within this region. However, the remaining isolates from Hainan, Guangdong, and Guangxi were clustered into two main genetic groups, with no significant genetic differentiation detected among the populations from these three provinces. This suggests frequent genetic exchange among P. polysora populations in Hainan, Guangdong, and Guangxi, leading to overall genetic homogeneity. These findings underscore the role of genetic connectivity in shaping the population structure of P. polysora in the pathogen's winter-reproductive regions, offering novel insights into its genetic dynamics. Furthermore, the results provide valuable information to support the development of effective strategies for managing P. polysora in China.

Cyproconazole (CPZ) was identified as a new postharvest fungicide with incomplete cross-resistance to other demethylation inhibitor fungicides registered for managing major decays of citrus. CPZ was effective on lemons, oranges, grapefruit, and mandarins, significantly reducing sour rot (Geotrichum citri-aurantii) and green mold (Penicillium digitatum). In laboratory and experimental packing line studies, CPZ was compatible with other fungicides, performed well in fruit coatings, and was effective using different application systems. CPZ at 300 to 1,250 μg/ml reduced sour rot incidence of lemons inoculated with a propiconazole (PPZ)-moderately resistant (MR) isolate of G. citri-aurantii from 87.5% in the control to between 54.6 and 13.3%, whereas. green mold caused by an imazalil (IMZ)-resistant (R) isolate of P. digitatum was reduced from 99.0% in the control to between 59.9 and 20.8%. CPZ at 1,000, 2,000, and 4,000 μg/ml in aqueous or storage coating preparations generally performed statistically similar against PPZ-sensitive (S), MR, and highly resistant (HR) isolates of G. citri-aurantii. Sour rot was reduced to zero levels with increasing concentrations for S, and MR isolates, whereas decay caused by the HR isolate was reduced from 97.1% in the control to 26.0% in storage wax treatments. For green mold and sporulation control, storage and pack coatings generally reduced the performance of CPZ, PPZ, IMZ, fludioxonil + azoxystrobin, and mixtures compared with aqueous applications. CPZ was not as effective as IMZ or fludioxonil + azoxystrobin in reducing sporulation. There was no significant difference in efficacy between heated and ambient-temperature flooder applications of CPZ or PPZ in controlling sour rot or green mold. CPZ is currently undergoing registration for postharvest use on citrus in the United States and will be an effective treatment by itself and in mixtures with other fungicides for major decays caused by S and R pathogens.

Citrus yellow vein clearing virus (CYVCV, Potexvirus citriflavivenae), an emerging pathogen that poses a threat to citrus production worldwide. To address this threat, three reverse transcription quantitative polymerase chain reaction (RT-qPCR) detection assays were developed and validated using all currently available public sequences and in-house high-throughput sequencing data from recent CYVCV detections in California, following guidelines for quantitative and qualitative real-time PCR experiments. Among the RT-qPCR assays tested, the CYVCV-4 outperformed others in analytical sensitivity, specificity, and diagnostic accuracy, demonstrating high amplification efficiency. The CYVCV-4 assay targets the RNA-dependent RNA polymerase gene of CYVCV and demonstrated high specificity by avoiding cross-reactivity and accurately identifying infected, non-infected, and non-target citrus pathogens. Its superior performance is attributed to optimized primer and probe design, enabling specific hybridization to the target sequence while minimizing non-specific amplification. The assay's robustness, inter-assay and intra-assay variation, and reproducibility were thoroughly validated across multiple labs, varying reaction conditions, and different qPCR instruments. Recent detections of CYVCV in California underscore the need for rapid and reliable diagnostics to protect citrus production and germplasm. The development and validation of the CYVCV-4 assay demonstrate its effectiveness through comprehensive testing, supporting its use in citrus diagnostic labs, quarantine programs, and field surveys, ultimately enhancing CYVCV management efforts. This development highlights the opportunity for plant diagnostics to adopt harmonized validation practices through frameworks like the Diagnostic Assay Validation Network, crucial for national programs, such as the National Clean Plant Network, which depend on validated assays to ensure clean plant systems and agricultural biosecurity.

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.