Phytopathology最新文献

One of the prominent bacterial diseases impacting orange production and trade is citrus canker, caused by the bacterium Xanthomonas citri subsp. citri (X. citri). The management of citrus canker involves deploying copper products as a protective measure to control the development of symptoms, which carries the risk of selecting strains that are resistant to copper. The objective in this report was to evaluate four peptides with potential antibiotic activity against X. citri in vitro and in planta. In growth inhibition assays, the peptides Gr01, Guavanin 2, K-13 and Lin1 had an inhibitory action on X. citri at concentrations below 12.5 µmol.L^-1. Minimal bactericidal effects were observed at peptide concentrations of 100 µmol.L^-1 and 50 µmol.L^-1 for Lin1 and Guavanin 2, respectively, and 12.5 µmol.L^-1 for Gr01 and K-13. Membrane mimetics coupled with fluorescence spectroscopy assays showed that Guavanin 2, Gr01 and K-13, but not Lin1, act by promoting bacterial membrane lysis. Moreover, the Gr01, K-13 and Lin1 peptides triggered a prolonged induction of genes associated with the activation of the jasmonic acid (JA) and salicylic acid (SA) pathways, suggesting a dual function of these peptides in promoting a priming effect. The severity of citrus canker in plants treated with Gr01, K-13 and Guavanin 2 was 0.2, 0.3 and 0.4 lesion/cm², respectively. These values were like those recorded in plants treated with copper (0.3 lesion/cm²) and significantly lower than the 1.5 lesion/cm² observed in untreated plants. Gr01 and K-13 peptides are promising dual-activity alternatives in the management of citrus canker.

Fire blight, caused by Erwinia amylovora, is one of the most devastating diseases of apple and pear worldwide. Young trees are particularly susceptible to the shoot blight phase of the disease, and the rapid downward spread of E. amylovora from infected shoot tips throughout trees to the rootstock often results in the formation of girdling cankers that kill trees. We quantified and tracked the systemic migration of E. amylovora cells in field studies through infected shoot tissues to gain insight into the systemic movement of the pathogen. In 2021 and 2022, bacterial populations were monitored over a 20-day period in defined sections of 'Gala' apple shoots in replicated field experiments. E. amylovora reached populations >10⁹ cfu g^-1 and maintained high populations in shoot tissue throughout the 20-day sampling period under conducive environmental conditions. E. amylovora cells migrated through shoot tissue at a maximum of 49.5 cm at 5 days after inoculation (9.9 cm day^-1) and exhibited an average velocity of 4.2 cm day^-1. The rate of migration through the new growth was 5.4 cm day^-1 and further investigations using scanning electron microscopy did not reveal major obstructions at the bud scar. Microscopic examination of infected shoot tissue enabled us to detect prolific colonization and bacterial ooze formation in the cortical parenchyma. Our study refines the fundamental knowledge of E. amylovora systemic colonization during shoot blight and contextualizes previously divergent studies of colonization from the past 50 years.

Brassinosteroid (BR) is essential in regulating plant growth and development and response to stress. However, there are few reports on the mechanism of BR regulating rice resistance to necrotrophic fungus. In this study, rice seedlings were pretreated with BR hormone and its synthetic inhibitor Brassinazole (BRZ) and inoculated with Rhizoctonia solani to analyze the reactive oxygen species (ROS), photosynthetic indices, and expression of phytohormones signal components and defense-related genes in rice leaves during pathogen infection. BR treatment significantly decreased the lesion area, significantly increased the activity of antioxidant enzymes and the content of antioxidant substances, and significantly decreased the contents of O₂-, H₂O₂, and MDA. At the same time, BR treatment enhanced photosynthetic pigment content and Fv/Fm value of rice seedlings. In addition, BR treatment can cause high expression of endogenous BR synthesis and decomposition genes and signal transduction genes, cooperate with SA, and antagonize JA signal gene expression. The structural equation analysis of tested indices uncovered firstly that high BR level stimulated the BR signal transduction pathway to regulate photosynthesis and ROS homeostasis through ROS signal, thereby enhancing the resistance of rice seedlings to R. solani. This study provides theoretical guidance for the application of BR analogues chemical regulators.

High-throughput phenotyping technologies increase the efficiency of breeding programs, but with larger data sets, errors can accumulate. Plant breeders often conduct quantitative trait locus (QTL) mapping, where large sample size and accurate quantitative response estimates are important for detecting small effect QTL. This study examined how phenotype error, inconsistency, and replication changed QTL magnitude and location. Three real sets of phenotype data were used from microscopy robot analysis of grapevine powdery mildew (Erysiphe necator) severity, which previously resulted in discovery of large (R² = 85%), intermediate (R² = 45%), and small (R² = 9%) effect QTL. Custom R scripts were written to induce several realistic sources of error, inconsistency, and varied replication. The results were remarkably robust to these changes. Swapping or shifting 2% of samples or changing disease severity by 50% on one replicate had negligible impact on QTL. Unreplicated simulations produced the largest LOD score range (5.55 to 8.27) and mean LOD score deviation (-1.72 to -3.22; Cohen's D = 1.48 to 2.12). The large effect size QTL (REN12) was always detected. The intermediate effect size QTL (REN13) was detected except when three of the eight replicates were analyzed individually. Even for the small effect size locus (NYVPLG9), error scenarios rarely (2 of 9000 cases) eliminated significant QTL detection, versus no replication (9 of 10). Thus, the benefits of data volume associated with high-throughput phenotyping technologies outweigh the cost of the increased errors tested here. Instead, focus should be spent on examining how each experimental replicate contributes to the result of the QTL mapping analysis.

Understanding the molecular and metabolic interplay between Meloidogyne incognita and soybean (Glycine max) root exudates is essential for unraveling plant-nematode interactions. This study investigates the transcriptomic responses of M. incognita during the pre-parasitic stage and the metabolomic changes in soybean root exudates influenced by nematode activity. Transcriptomic analysis identified 846 differentially expressed genes in nematodes exposed to root exudates (S-Mi) compared to nematodes alone (Mi). Upregulated genes, including those encoding sensory receptors such as G-protein coupled receptors, nuclear hormone receptors, acetylcholine receptors (AChRs), and key effectors, indicate a shift toward parasitic readiness. The downregulation of detoxification genes (e.g., cytochrome P450) and the upregulation of lysosome-related genes, such as cathepsins L-like cysteine proteases suggest metabolic reprogramming to support infection. Metabolomic profiling identified 781 metabolites across S-Mi, Mi, and Soy (root exudates alone), with enriched pathways such as tyrosine metabolism and cytochrome P450-related detoxification. Interestingly, amino acids like L-threonine and arginylthreonine were upregulated in S-Mi, suggesting their role in nematode attraction. Additionally, lipid-like metabolites, such as 3-epipapyriferic acid and physagulin F, were elevated, potentially influencing nematode behavior and modulating plant defense response. An integrated cellular model illustrates how nematode sensory receptors detect root signals, activating cAMP, PLC, and MAPK signaling cascades, as well as AChR-mediated ion channels, leading to effector gene activation and metabolic shifts. This study reveals a bidirectional interaction at the pre-parasitic stage, where soybean root exudates reprogram nematode metabolism, while nematodes, in turn, modify root exudates to influence plant defenses, offering novel targets for sustainable nematode management.

Cucurbit yellow vine disease (CYVD) is an emerging disease that can cause up to 100% cucurbit crop losses. CYVD is transmitted by squash bugs (Anasa tristis), but anecdotal reports indicate the presence of CYVD in cucurbit fields in the apparent absence of squash bugs and presence of cucumber beetles. This study tested the vector competence of two cucumber beetle species (Acalymma vittatum and Diabrotica undecimpunctata howardi) for CYVD and explored the phylogenetic relatedness of CYVD-causing isolates (i.e., CYVD strains) from cucurbits to those from wild cucumber beetles from fields with endemic CYVD. CYVD strains have heretofore been classified as Serratia marcescens; however, pairwise genomic comparisons and phylogenomic analyses using complete genome assemblies of five CYVD strains, including two from wild cucumber beetles, indicate that CYVD strains form a clade in the Serratia ureilytica species, which is a species within the S. marcescens complex. The S. ureilytica isolates from both cucumber beetle species were pathogenic based on their ability to induce CYVD when injected into squash (Cucurbita pepo) plants. Moreover, field-collected cucumber beetles of both species harboring the CYVD pathogen induced CYVD in squash plants in laboratory transmission tests, demonstrating that cucumber beetles can transmit S. ureilytica to plants. Our results support a nomenclature change for the causal agent of CYVD to S. ureilytica and demonstrate that cucumber beetles can both harbor and transmit S. ureilytica CYVD strains. S. ureilytica is thus distinct among phytopathogenic bacteria in its ability to use both hemipterans and coleopterans as vectors for transmission to plants.

Rice XA21 is the cognate resistance (R) protein of the avirulence protein AvrXA21 (RaxX) of Xanthomonas oryzae pv. oryzae (Xoo). RaxX precursor must be modified by the peptidase RaxB and the tyrosine sulfotransferase RaxST to transform into an active form that has ability to bind and active XA21. We previously found that a small protein, RaxM, regulates raxX expression, and thus affects XA21-mediated immunity response. However, the mechanism that through which RaxM regulates raxX expression remains unknown. Here we showed that RaxM can interact with MutL and enhance its endonuclease activity in Xoo. Mutation of mutL increased raxM expression but decreased raxX expression. In addition, MutL also positively regulated the expression of raxST and raxR that are required for raxX expression or modification. Therefore, mutL mutation increased Xoo virulence on XA21-expressing rice. These findings indicate that RaxM regulates raxX expression and modification by influencing MutL activity, and thus regulates RaxX-mediated immune response.

Over the past five years, seedling diseases have caused an average annual loss of $21.8 million dollars' worth of United States' soybean (Glycine max (L.) Merr.) production, with Fusarium graminearum (teleomorph Gibberella zeae (Schwein.) Petch) emerging as a significant threat within the seedling disease complex. Its cross-pathogenicity on wheat and maize, along with increasing reports of fungicide resistance, highlights the need for improved genetic resistance in soybean. In a previous germplasm screening and genome-wide association study (GWAS) we identified a significantly resistant accession, PI 438500, from a panel of 208 diverse soybean accessions. This accession carried fewer marker-trait associations (MTAs) and lower predicted resistance than other significantly resistant accessions yet displayed a highly resistant phenotype with low standard deviations. In this study, we developed an F_2:3 mapping population from a bi-parental cross between PI 438500 and PI 548631 (highly susceptible to F. graminearum) and identified a quantitative trait locus (QTL) that explains 20.29% of the variation in post-emergent visual severity. This QTL region contains multiple candidate genes with predicted roles in plant defense mechanisms and helps elucidate PI 438500's significant resistance to F. graminearum. Molecular markers linked and within this QTL region can help facilitate marker-assisted selection for F. graminearum resistance in soybean breeding.

Wheat stem rust caused by the obligate biotrophic fungal pathogen Puccinia graminis f. sp. tritici (Pgt) is an important disease of barley and wheat worldwide. Alarmingly, the Pacific Northwest (PNW) contains a highly virulent Pgt population on barley. This population includes the Pgt isolate Lsp21 which is virulent on the barley stem rust resistance genes Rpg1, Rpg2, Rpg3, rpg4, Rpg5, and rpg8. The virulence on barley lines containing Rpg1 and the rpg4/Rpg5-mediated resistance locus (RMRL), when stacked together is a Pgt virulence profile on barley that had not been previously reported, thus, represents the most virulent Pgt isolates on barley R-genes characterized worldwide. The line Elliot (PI 592261) was identified from the world barley core collection as containing effective seedling resistance to Pgt isolate Lsp21. To genetically characterize the resistance present in Elliot, 129 recombinant inbred lines were developed by advancing a population from the cross Elliot (resistant) x Palmer (susceptible) to the F₆ generation. The population was phenotyped with Pgt isolate Lsp21 at the seedling stage and genotyped with the Illumina 50K bead express SNP chip, resulting in 7,284 high-quality SNP markers. Two significant resistance QTL (EPRpg_4H-1 and EPRpg_5H-1) contributed by Elliot were identified on chromosomes 4H and 5H, respectively. The major QTL, EPRpg_4H-1, is novel, while EPRpg_5H-1 localized to a region ~9 Mbp distal of RMRL within a region of the barley genome that contains previously identified stem rust resistance loci. These QTL should be useful in developing barley cultivars with resistance to the virulent PNW Pgt population.

Plant-parasitic nematodes (PPNs) cause billions of dollars in agricultural losses annually. In the United States (U.S.), a well-established list of prevalent nematodes serves as a foundation for addressing known threats. However, climate change is expected to trigger significant shifts in nematode populations, behaviors, and host ranges, introducing new risks to agricultural ecosystems. Understanding how nematodes adapt to evolving environments is crucial for predicting their spread to new locations and hosts. Beyond the spread of current PPN populations, there is the ongoing threat of undetected or non-native PPNs entering the U.S., potentially causing severe damage to agriculture and forest ecosystems. Continuous surveillance is vital to track nematode spread, and advancements, such as machine learning for nematode detection and quantification, enhance diagnostic capabilities. Additionally, remote sensing combined with geographic information systems is emerging as a powerful tool for pest management, offering spatial analysis and real-time monitoring. In this review, we highlight a selection of PPN species, including those with currently limited geographic distribution but posing a significant threat if introduced to new environments. We list these nematodes based on their host range, potential economic impact, and current molecular diagnostic methods. We propose the "Emergence Triangle" to explore how abiotic stresses impact nematode adaptation and how nematologists use innovative technologies to enhance surveillance efforts. While ongoing diagnostic and monitoring efforts provide valuable insights, continuous surveillance is essential to track nematode spread. Critical questions remain regarding the criteria used by government officials to classify and regulate nematodes and who guides decisions on prioritizing threats.