Phytopathology最新文献

Wheat blast caused by the fungus Magnaporthe oryzae Triticum (MoT) pathotype is a catastrophic disease that threatens global food security. Recently, Rmg8 was discovered as a blast resistance gene in wheat genotype S615. However, although Rmg8 has recently been cloned, the precise underlying biochemical and molecular mechanisms by which this gene confers resistance against MoT remain to be fully elucidated. This study investigated the antioxidant defense mechanisms in the wheat genotype S615, which carries the blast resistance gene Rmg8 against MoT infection, compared with the blast-susceptible wheat variety BARI Gom-26 (BG26). Artificial inoculation of wheat heads with MoT followed by biochemical analyses revealed that the levels of hydrogen peroxide (H₂O₂), lipoxygenases (LOXs), and malondialdehyde (MDA) in rachis tissues increased significantly until 48 h after inoculation in both S615 and BG26. However, LOX and MDA concentrations were substantially lower in S615 than in BG26. These biochemical alterations may have contributed to less damage to photosynthetic pigments, such as chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids in the rachis of S615. The S615 genotype exhibited significantly higher levels of several enzymatic (superoxide dismutase, catalase, ascorbate peroxidase, glutathione peroxidase, glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase) and non-enzymatic (e.g., proline) antioxidants in the MoT-inoculated rachis tissues than in those of BG26. To the best of our knowledge, this study biochemically demonstrates for the first time that the blast resistance in S615 is, in part, correlated with its strong antioxidant defense responses to MoT infection, providing a physiological basis for this resistance mechanism.

In this study, we used coniferous and non-coniferous hosts to assess pathogenicity of a Fusarium annulatum isolate derived from southwestern white pine (Pinus strobiformis), along with F. commune isolates derived from coniferous and herbaceous, non-conifer hosts. All isolates of both Fusarium spp. were found to be pathogenic to conifer hosts. For the tested non-coniferous hosts, F. commune isolates were found pathogenic to both rice and tomato, while F. annulatum was only found pathogenic to rice. To investigate the molecular basis of pathogenicity, we identified differentially expressed pathogenicity-/virulence-associated genes by inoculating loblolly pine (P. taeda) seedlings with isolates of conifer-derived F. commune (collected from ponderosa pine [P. ponderosa]) and F. annulatum (collected from southwestern white pine), which were all previously confirmed pathogenic to loblolly pine in our assays. Seedlings were harvested at 12-, 24-, and 48-hours post-inoculation for transcriptomic analyses to identify pathogen genes associated with early infection of the host. Among the upregulated in planta (UIP) genes, we identified putative pathogenicity-/virulence-associated genes including secreted effectors, secondary metabolite gene clusters involved in mycotoxin biosynthesis, and carbohydrate-active enzymes. To identify putative conifer pathogenicity profiles of these potential conifer pathogens, we compared these UIP genes with the predicted proteomes of 17 conifer-associated Fusarium spp. isolates. While these putative pathogenicity profiles did not definitively correspond with pathogenicity on coniferous versus herbaceous hosts, but rather aligned with Fusarium species complexes. A subset of these shared UIP genes may aid in the development of detection methods for conifer-specific pathogens based on Fusarium species complexes.

Colletotrichum fructicola is a significant phytopathogen in both pre- and postharvest stages of fruit development and storage. The development of environmentally friendly biological control agents has attracted increasing research interest. In this study, we characterized a fungal strain (Epicoccum layuense LQ) that strongly inhibits C. fructicola. A potato dextrose broth culture filtrate of strain LQ inhibited the vegetative growth of C. fructicola by approximately 80% at a 1:10 (vol/vol) dilution. Cytological observations revealed that the filtrate disrupted mitosis and cellular polarity during conidial germination. Furthermore, the culture filtrate effectively suppressed C. fructicola infection on both apple leaves and fruits. The fungal strain LQ was identified as E. layuense through integrated morphological characterization and multilocus phylogenetic analysis. Whole-genome sequencing of strain LQ identified 36 biosynthetic gene clusters (BGCs), and subsequent gene synteny analysis demonstrated structural conservation in three BGCs homologous to known antifungal clusters. Notably, substitution of NaNO₃ with yeast extract in a Czapek-Dox medium enhanced the antifungal activity of the strain LQ filtrate by 14.2-fold. Consistent with this finding, transcriptomic profiling revealed significant upregulation of BGCs associated with epipyrone A and burnettramic acid A biosynthesis under a yeast extract supplementation condition. In sum, our results demonstrate the antagonistic potential of E. layuense LQ and identify two candidate BGCs that may mediate this biocontrol activity, which lays a foundation for further mechanism dissection.

Rice blast, caused by the ascomycete fungus Magnaporthe oryzae, is one of the most problematic diseases for rice production, threatening global food security. Genetic resistance to some M. oryzae races can be achieved using major resistance genes that recognize their corresponding fungal avirulence genes. Weedy rice, a close relative of cultivated rice that competes with the crop, has evolved unique genetic mechanisms to resist M. oryzae infections; thus, weedy rice can serve as an excellent resource for blast control. In this study, we assessed disease scores of 183 F₅ and F₆ recombinant inbred lines (RILs) derived from a weedy rice × crop biparental mapping population and their parental lines, a Black Hull Awn weedy rice strain (PI 653413, RR14) and the aus-196 rice variety, using four distinct common U.S. blast races (IB33, IG1, IE1K, and IC17) under greenhouse conditions. All the parental lines were resistant to all blast races; however, RILs showed a wide degree of variation in resistance. Genotyping-by-sequencing of the RIL population and parents generated 1,498 single-nucleotide polymorphisms, which were used to construct a linkage map, and quantitative trait locus (QTL) mapping of blast resistance was performed using r/qtl. A single major blast resistance QTL on chromosome 12 was mapped to the Pi-ta/Pi39(t)/Ptr locus. Identification of Pi-ta/Pi-39(t)/Ptr as the key contributor to blast resistance in weedy rice provides insight into the evolution and adaptation of weedy rice and can aid in the development of blast-resistant rice varieties through marker-assisted selection.

Wheat yellow mosaic virus (WYMV) is the main cause of wheat yellow mosaic disease. Although its regulation of protein translation and interactions with host proteins are well studied, independent regulation of the virus genome is poorly understood. This study performed in vitro experiments investigating replication regulation by the 5' and 3' untranslated regions of WYMV RNA2. The results confirm that the RNA-dependent RNA polymerase (nuclear inclusion protein b [NIb]) can only recognize and catalyze the synthesis of 3' 190-nt complementary chains in vitro. RNA structure probing and mutation analysis identified ³⁵⁹⁷AUU and ³⁶⁰⁷GGCU as novel interaction sites of NIb; both are essential for maintaining normal replication. Our findings provide an empirical basis for in vivo experiments on regulation of WYMV genome replication and provide a theoretical basis for the prevention and control of WYMV-related crop diseases.

Infection by aphid-transmitted poleroviruses modulates gene expression associated with plant development and defense. This study assessed the gene expression patterns following cotton leafroll dwarf virus (CLRDV) infection in primary and alternate hosts. Two comparisons (CLRDV-infected vs. non-infested and mock-inoculated vs. non-infested) were evaluated to identify differentially expressed genes (DEGs), and to tease out differences in gene expression profiles between aphid feeding and aphid-mediated CLRDV infection in each host. CLRDV infection was characterized by 2079, 1238, 1484, and 1773 DEGs in the primary host cotton, and in alternate hosts hibiscus, okra, and prickly sida, respectively. The number of DEGs upon aphid feeding was less than CLRDV infection in all hosts except okra. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) terms identified DEGs associated with development, defense, and vector fitness influencing compounds (VFICs) in CLRDV-infected plants. Genes associated with phytohormones, photosynthesis, salicylic acid, jasmonic acid, pathogenesis related proteins, heat shock proteins, transcription factors, membrane transporters, terpenoids, carbohydrates, and amino acids were differentially expressed in CLRDV-infected plants and varied between hosts. Few overlapping and numerous unique genes in the above-stated categories were differentially expressed upon aphid feeding and varied between hosts. DEGs associated with signaling pathways, transcription factors, systemic resistance, pathogenesis related proteins, and carbohydrate and amino acid biosynthesis were common between aphid-mediated CLRDV infection and aphid feeding alone. The observed gene expression patterns reiterate that differences in host susceptibility to the virus and/or the vector could differentially influence host defense and development, and vector fitness.

Sweet cherry (Prunus avium L.) is a commercially vital fruit crop in China. The hop stunt viroid (HSVd) infection in sweet cherry causes dappled fruit. This study investigated the mechanism of dappled fruit formation in HSVd-infected sweet cherry using integrated metabolomics and transcriptomics. Dappled and non-dappled peel tissues were sampled at the color change and ripening stages. UPLC-MS/MS identified 181 flavonoid metabolites, with peonidin-3-O-rutinoside, cyanidin-3-O-glucoside, peonidin-3-O-glucoside, cyanidin-3-O-arabinoside, cyanidin 3-xyloside and cinchonain Ic being significantly enriched in dappled areas. RNA-seq revealed 3,287 differentially expressed genes, with PaCHS, PaCHI, PaDFR, and PaANS up-regulated in dappled areas at the early stage, correlating with anthocyanin accumulation. KEGG enrichment highlighted anthocyanin and flavonoid biosynthesis pathways as central to pigmentation. This study suggests that HSVd disrupts anthocyanin biosynthesis to induce dappled pigmentation, offering novel insights into viroid-host interactions affecting fruit color in sweet cherry.

The spread of Phytophthora ramorum, the causal agent of Sudden Oak Death and Sudden Larch Death, has resulted in a destructive loss of trees, woody shrubs, and ornamentals in nurseries and forests in the US, Canada, and Europe since the late 1990s. Twelve lineages of P. ramorum are described that vary in global distribution and virulence. Herein, we present a maximum likelihood phylogeny for P. ramorum inferred using IQ-TREE and Tree-Based Alignment Selector Toolkit (T-BAS). The phylogeny was generated based on six loci (avh120, avh121, btub, gweuk.30.30.1, hsp90, and trp1). This phylogeny of P. ramorum improves on previous phylogenies since it is dynamic and interactive and incorporates a diverse set of all known global lineages from the US, Europe (NA1, NA2, EU1, and EU2), and ancestral lineages from the putative native range in East Asia. The phylogenetic relationships inferred in the T-BAS tree support lineages NP1 and NP2 of P. ramorum as ancestral to NA1 and NA2 lineages found in North America. In addition, East Asian IC1, IC2, IC3, and IC4 lineages are ancestral to EU1 and EU2 lineages found in Europe. We used sequence data generated from isolates of P. ramorum collected from Ireland and Northern Ireland and placed them accurately in the tree. The P. ramorum phylogeny is available through T-BAS within the DeCIFR platform. This "interactive phylogeny" can be used by the research community to rapidly update and better reflect the evolutionary relationships of new lineages of P. ramorum.

Sclerotinia sclerotiorum causes Sclerotinia stem rot, or white mold, on multiple economically important crops in Michigan. Soybean farmers and crop consultants in the Midwestern U.S. currently use S. sclerotiorum apothecia prediction models to inform fungicide application timing to optimize disease control and economic return. However, current models have not been validated for use in dry bean or potato and do not account for the effects of irrigation on apothecia development. To improve S. sclerotiorum apothecia prediction, on-site weather data were collected and used to generate new binomial logistic regression (LR) and supervised machine learning (ML) models for irrigated soybean, dry bean and potato fields. The ML algorithms investigated included decision trees, random forests and support vectors machines. Decision tree classification models outperformed LR and other ML models, achieving 77% accuracy on testing data. Accuracy increased to 89% when on-site weather data were included, indicating that on-site weather monitoring may be required to reliably predict apothecia presence in irrigated environments. Feature importance analysis identified row shading (the distance the plant canopy extends into the row) as critical for prediction accuracy. The minimum row shading required to trigger apothecia development varied slightly between crop types and row spacings, from 0.15 to 0.21m. Apothecia density peaked when soil temperatures were 21.51°C and volumetric water content were 11.43% and 19.58%. Additionally, a rapid increase in apothecia presence was observed after canopy closure reached 87%. Future model testing and validation will be required prior to deployment as a decision aid for farmers and crop consultants.

Citrus canker, caused by Xanthomonas citri pv. citri, is one of the most devastating bacterial diseases of citrus species. The global population of Xanthomonas citri pv. citri includes three lineages designated as pathotypes A, A* and A^w. While pathotype A is the most prevalent lineage around the world, the citrus canker pathogen in Iran includes only pathotype A* strains. Previous work on the Xanthomonas citri pv. citri strains collected before 2013 showed that two lineages of the pathogen presented in Iran, i.e., 4.1 and 4.4, with 4.4 not present anywhere else at that time. In this study, using a new set of strains collected in 2021-2022, we re-assessed the population structure of the pathogen in Iran using a phylogeographic approach. All strains isolated in Iran still belonged to pathotype A*. Multilocus variable number tandem repeat analysis (MLVA) revealed that 62 Iranian strains collected between 1991-2022 were distributed among 22 haplotypes. Four new haplotypes were identified within the strains isolated in this study which have not previously been reported elsewhere in the world. Although all pre-2013 strains isolated in Sistan-Baluchestan Province of Iran were grouped in subcluster 4.4, all post-2020 strains isolated in the same area were identified as members of subcluster 4.1. None of the post-2020 strains isolated in Iran belonged to subcluster 4.4, which suggests a shift in population structure of the pathogen over the past two decades. Our data would pave the way of research on the population structure of citrus canker pathogen in the area.