Phytophthora Capsici Research Articles

Resistance risk and resistance-associated point mutations in the target protein PcVHA-a of fluopimomide in Phytophthora capsici

Fluopimomide, developed by Shandong Sino-Agri United Biotechnology Co., Ltd., is a pyridinylmethyl-benzamide fungicide with good activity against plant diseases caused by phytopathogenic oomycetes. However, there is uncertainty surrounding the resistance risk of fluopimomide and its resistance mechanism in Phytophthora capsici. In this study, the baseline sensitivity of P. capsici to fluopimomide was established, and 106 P. capsici isolates shown sensitive to fluopimomide, with a mean EC50 value of 5.1892 ± 2.2613 μg/mL. Fungicide adaptation produced three fluopimomide-resistant P. capsici mutants, two of which exhibited considerably lower compound fitness index (CFI) than the parent strain, and one showed significantly improved CFI. While cross-resistance was observed between fluopimomide and fluopicolide, no cross-resistance was detected between fluopimomide and other fungicides. Overall, P. capsici presents a moderate resistance risk to fluopimomide. Two point mutations, G767E and K847R, were identified in the V-ATPase subunit a of P. capsici (PcVHA-a) in resistant mutants. These mutations were subsequently validated through site-directed mutagenesis and molecular docking assays, confirming their role in conferring fluopimomide resistance in P. capsici.

Space-time analysis, severity of the wilt disease in escabeche pepper (Capsicum baccatum var. Pendulum) and identification of the causal agent (Phytophthora capsici L.) under subtropical climate conditions in Peru

Phytophthora capsici is an aggressive pathogen in escabeche pepper on the Peruvian coast. Root rot has a strong correlation with humidity and environment. Disease behavior was evaluated epidemiologically using spatiotemporal variables. Severity was evaluated according to the advance of the secondary symptom according to grades 1 to 5. Then, coordinates of each plant were established by photogrammetric survey of a field with 1705 escabeche pepper plants. For temporal analysis, severity was adjusted to an exponential model (R2 = 0.909) and incidence to a Gompertz model (R2 = 0.921) that detected an initial delay of the disease due to temperature. For the spatial analysis, the Global Moran Index (Ii) showed a high spatial dependence of the disease reaching a peak of 0.4 and 0.7 for severity and incidence, respectively. Also, heat maps related to the Local Ii were generated from which an initial source of infestation was determined where the furrow irrigation started in random infestations. Then, the infestation spots were settled in areas of surface water accumulation. Also, rhizosphere samples were collected per plant by degree of severity on V8 or CMA whit PARB and PDA-A selective medium. As a result, significant differences were obtained between grade 1, grade 2, 3, 4 and grade 5. In addition, the effect on yield was significant for plants with grade 4 and 5 with respect to fruit weight (22.3 and 18.5g/fruit) and weight per plant (509.5 and 371.8g/plant), respectively.

Gene markers generating polygenic resistance in melon-Fusarium wilt-FOM1.2 interaction pathosystem.

Developing melon genotypes with resistance to Fusarium oxysporum f. sp. Melonis-(FOM) race1.2 is a major goal in any breeding program. In this study, we identified the role of 11 gene markers that contribute to polygenic resistance during the FOM1.2-melon interaction. qRT-PCR analysis elucidated upregulation of candidate marker genes AMT, DXPR, Fom-2, GLUC, GalS, GRF3, MLO, PRK, RuBlsCo, TLP and WRKY in resistant 'Shante-F1' and 'Khatouni', and susceptible 'Shante-T' and 'Shahabadi' at 7, 14 and 21 days post-inoculation (dpi). We also studied changes in defence-related enzyme activity: chitinase (CHI), β-1,3-glucanase (GLU) and peroxidase (POX) in melon roots. AMT, GLUC and DXPR transcripts were upregulatied in leaf and root tissues of the resistant 'Shante-F1' and 'Shahabadi'. Transcript levels for GalS and GRF3 increased 6.77- and 6.83-fold in roots of 'Shante-F1' at 7 dpi, whereas in PRK, TLP and WRKY theye increased by 7.84-, 5.15- and 12.26-fold at 14 dpi, respectively. However, transcript levels increased by 5.18-fold for Fom-2 and 8.46-fold for MLO at 21 dpi. Also, RBC transcript level peaked at 14 dpi with 4.9-fold increase in leaves of resistant genotypes, whereas AMT increased 2.94-fold at 21 dpi, and GLUC and DXPR increased 7.11- and 2.91-fold at 14 dpi in 'Shante-F', respectively. Defence-related-enzyme activity was also upregulated three-fold in resistant varieties. The dynamic shifts in the melon transcriptome induced by FOM1.2 emphasize that resistance mechanisms are predominantly regulated through signalling pathways involving CHI, GLU, and POX defence response. Surprisingly, the AMT gene, basically resistant to downy mildew, Pseudoperonospora cubensis; GLUC, MLO and PRK resistant to powdery mildew (Sphaerotheca fusca); TLP and WRKY resistant to Phytophthora blight (Phytophthora capsici); and GRF3 and RBC resistant to root knot nematodes (Meloidogyne spp.) were upregulated in resistant genotypes, indicating a dual role of these genes in resistance to more than one disease at a time.

CaARP1/CaSGT1 Module Regulates Vegetative Growth and Defense Response of Pepper Plants against Phytophthora capsici

Pepper (Capsicum annuum L.) suffers severe quality and yield loss from oomycete diseases caused by Phytophthora capsici. CaSGT1 was previously determined to positively regulate the immune response of pepper plants against P. capsici, but by which mechanism remains elusive. In the present study, the potential interacting proteins of CaSGT1 were isolated from pepper using a yeast two-hybrid system, among which CaARP1 was determined to interact with CaSGT1 via bimolecular fluorescence complementation (BiFC) and microscale thermophoresis (MST) assays. CaARP1 belongs to the auxin-repressed protein family, which is well-known to function in modulating plant growth. The transcriptional and protein levels of CaARP1 were both significantly induced by infection with P. capsici. Silencing of CaARP1 promotes the vegetative growth of pepper plants and attenuates its disease resistance to P. capsici, as well as compromising the hypersensitive response-like cell death in pepper leaves induced by PcINF1, a well-characterized typical PAMP from P. capsici. Chitin-induced transient expression of CaARP1 in pepper leaves enhanced its disease resistance to P. capsici, which is amplified by CaSGT1 co-expression as a positive regulator. Taken together, our result revealed that CaARP1 plays a dual role in the pepper, negatively regulating the vegetative growth and positively regulating plant immunity against P. capsici in a manner associated with CaSGT1.

Non-food renewable and bioactive products for pesticides: Synthesis, anti-oomycete and anti-fungal activities of 9R-acyloxyquinine derivatives bearing an 1,3,4-oxadiazole moiety

Quinine is the main alkaloids in the bark of Cinchona and its homologous plants of Rubiaceae. To discover biorational natural product-based pesticides, a series of 9R-acyloxyquinine derivatives containing 1,3,4-oxadiazole moieties were prepared by ingeniously introducing an active ester group and a 1,3,4-oxadiazole five membered heterocyclic ring at its C-9 position, and their structures were well characterized by 1H NMR, 13C NMR, HRMS, and m.p. The stereochemical configuration of target compound 6 t was unambiguously subjected to single-crystal X-ray diffraction. Furthermore, bioactivities of these compounds as anti-oomycete and anti-fungal agents against two serious agricultural diseases, Phytophthora capsici and Fusarium graminearum we assessed. Among all tested compounds, 1) Compounds 6c and 6d displayed promising anti-oomycete against P. capsici, with EC50 values of 38.42 and 35.49 mg/L, respectively. 2) Compound 6i exhibited promising anti-fungal against F. graminearum, with an EC50 value of 29.92 mg/L. Moreover, some interesting results of structure-activity relationships were also observed. The results of this study pave the way for further design, structural modification, and development of quinine derivatives as plant anti-oomycetes and anti-fungal agents in crop protection.

Intra species dissection of phytophthora capsici resistance in black pepper

IntroductionBlack pepper, a financially significant tropical crop, assumes a pivotal role in global agriculture for the major source of specie flavor. Nonetheless, the growth and productivity of black pepper face severe impediments due to the destructive pathogen Phytophthora capsici, ultimately resulting in black pepper blight. The dissecting for the genetic source of pathogen resistance for black pepper is beneficial for its global production. The genetic sources include the variations on gene coding sequences, transcription capabilities and epigenetic modifications, which exerts hierarchy of influences on plant defense against pathogen. However, the understanding of genetic source of disease resistance in black pepper remains limited. MethodsThe wild species Piper flaviflorum (P. flaviflorum, Pf) is known for blight resistance, while the cultivated species P. nigrum is susceptible. To dissecting the genetic sources of pathogen resistance for black pepper, the chromatin modification on H3K4me3 and transcriptome of black pepper species were profiled for genome wide comparative studies, applied with CUT&Tag and RNA sequencing technologies. ResultsThe intraspecies difference between P. flaviflorum and P. nigrum on gene body region led to coding variations on 5137 genes, including 359 gene with biotic stress responses and regulation. P. flaviflorum exhibited a more comprehensive resistance response to Phytophthora capsica in terms of transcriptome features. The pathogen responsive transcribing was significant associated with histone modification mark of H3K4me3 in black pepper. The collective data on variations of sequence, transcription activity and chromatin structure lead to an exclusive jasmonic acid-responsive pathway for disease resistance in P. flaviflorum was revealed. This research provides a comprehensive frame work to identify the fine genetic source for pathogen resistance from wild species of black pepper.

Transcriptional regulation of hormone signalling genes in black pepper in response to Phytophthora capsici

IntroductionBlack pepper (Piper nigrum L.) is a non-model spice crop of significant agricultural and biological importance. The ‘quick wilt’ disease caused by the oomycete Phytophthora capsici is a major threat, leading to substantial crop loss. The molecular mechanisms governing the plant immune responses to this pathogen remain unclear. This study employs RNA sequencing and transcriptome analysis to explore the defense mechanisms of P. nigrum against P. capsici.ResultsTwo-month-old P. nigrum plantlets were subjected to infection with P. capsici, and leaf samples were collected at 6- and 12-hours post-inoculation. RNA was extracted, sequenced, and the resulting data were processed and assembled. Differential gene expression analysis was conducted to identify genes responding to the infection. Additionally, the study investigated the involvement of Salicylic acid (SA), Jasmonic acid (JA), and Ethylene (ET) signalling pathways. Our transcriptome assembly comprised 64,667 transcripts with 96.7% completeness, providing valuable insights into the P. nigrum transcriptome. Annotation of these transcripts identified functional categories and domains, provided details on molecular processes. Gene expression analysis identified 4,714 transcripts at 6 h post-infection (hpi) and 9,416 at 12 hpi as differentially expressed, revealing dynamic regulation of immune-related genes. Furthermore, the study investigated key genes involved in biosynthesis pathways of Salicylic acid, Jasmonic acid, and Ethylene signalling. Notably, we found differential regulation of critical genes associated with these pathways while comparing data before and after infection, thereby shedding light on their roles in defense mechanism in P. nigrum defense.ConclusionsThis comprehensive transcriptome analysis of P. nigrum response to P. capsici attack provides valuable insights into the plant defense mechanisms. The dynamic regulation of innate immunity and the involvement of key signalling pathways highlight the complexity of the plant-pathogen interaction. This study contributes to our understanding of plant immunity and offers potential strategies for enhancing P. nigrum resistance to this harmful pathogen.

Carbon and Nitrogen Sources Influence Parasitic Responsiveness in Trichoderma atroviride NI-1.

Parasitic species of Trichoderma use hydrolytic enzymes to destroy the host cell wall. Preferent carbon and nitrogen sources suppress the expression of genes related to parasitism. Here, different nutrients were evaluated in the parasitic isolated NI-1, which was identified as Trichoderma atroviride. The genes cbh1 and chb2 (cellobiohydrolases), bgl3.1 (endoglucanase), and pra1 and prb1 (proteinases) were poorly expressed during the interaction between NI-1 and Phytophthora capsici on PDA. However, gene expression improved on minimal medium with preferent and alternative carbon sources. Dextrin and glucose stimulated higher transcript levels than cellulose, sucrose, and glycerol. Also, ammonium stimulated a stronger parasitic responsiveness than the alternative nitrogen sources. During interaction against different phytopathogens, NI-1 detects their host differentially from a distance due to the cbh1 and cbh2 genes being only induced by P. capsici. The pra1 and ech42 genes were induced before contact with Botrytis cinerea and Rhizoctonia solani, while when confronted with P. capsici they were stimulated until contact and overgrowth. The prb1 and bgl3.1 genes were induced before contact against the three-host assayed. Overall, T. atroviride prefers to parasitize and has the capacity to distinguish between an oomycete and a fungus, but nutrient quality regulates its parasitic responsiveness.

Next-generation sequencing-based comparative mapping and culture-based screening of bacterial rhizobiome in Phytophthora capsici-resistant and susceptible Piper species.

Black pepper (Piper nigrum L.), a highly valued spice crop, is economically significant as one of the most widely traded spices in the world. The global yield and quality of black pepper (Piper nigrum L.) are affected by foot rot-causing soil-borne oomycete pathogen Phytophthora capsici. To gain initial insights toward developing an approach that utilizes microbial genetic resources for controlling foot rot disease in black pepper, we mapped the rhizobiome communities in susceptible Piper nigrum L. and wild-resistant Piper colubrinum. The analysis showed compositional differences in the rhizobiome of two Piper species, which revealed higher diversity and the presence of more differentially abundant genera in P. colubrinum. Furthermore, P. colubrinum rhizobiome had a significantly higher abundance of known anti-oomycete genera, such as Pseudomonas, and a higher differential abundance of Janthinobacterium, Variovorax, and Comamonas, indicating their probable contribution to pathogen resistance. Predictive functional profiling in P. colubrinum rhizobiome showed highly enriched functional gene orthologs (KOs), particularly chemotaxis proteins, osmoprotectants, and other transport systems that aid in pathogen resistance. Similarly, pathways such as phenylpropanoid biosynthesis and other antimicrobial synthesis were enriched in P. colubrinum rhizobiome. The culturable diversity of the resistant root endosphere, which harbors efficient biocontrol agents such as Pseudomonas, strengthens the possible role of root microbiome in conferring resistance against soil-borne pathogens. Our results depicted a clear distinction in the rhizobiome architecture of resistant and susceptible Piper spp., suggesting its influence in recruiting bacterial communities that probably contribute to pathogen resistance.

Evaluation of biocontrol efficacy of rhizosphere Pseudomonas aeruginosa for management of Phytophthora capsici of pepper

Evaluation of biocontrol efficacy of rhizosphere Pseudomonas aeruginosa for management of Phytophthora capsici of pepper

Isolation, identification and multi-locus sequence typing of Phytophthora capsici from capsicum fields and its cross-infectivity in different crop species

Phytophthora capsici is a major soil-borne oomycete plant pathogen, which severely affects the productivity of peppers including Capsicum annuum L., by causing fruit rot, root rot, and foliar blight diseases. It has a broad host range beyond Capsicum species and evolves rapidly to find new potential hosts for survival under different climatic conditions. In the present study, P. capsici was isolated from soil using castor seed baiting, and characterized through growth patterns and spore morphology. The species identification and molecular characterization were achieved through multi-locus sequence and phylogenetic analysis of three genomic loci (ITS, tef1 and cox), and also attributed given P. capsici isolate Pc_UHF into India-specific ITS-based evolutionary lineage Pc-X. Interestingly, dN/dS estimates revealed reasonably high positive selection in the tef1 gene, which could have possible implications on the pathogen's adaptation and/or virulence. Pathogenicity of this isolate was tested in three commercially growing bell pepper varieties and also in other crop species using detached leaf and/or in planta disease screening. Differential disease symptoms were induced by Pc_UHF in three bell pepper varieties, such as both collar rot and foliar blight symptoms observed in "Yolo Wonder" and "California Wonder", whereas only foliar blight symptoms were recorded in "Solan Bharpur". Furthermore, cross-pathogenicity was also recorded in tomato, citrus, cucumber and eggplant. This is the first report of molecular characterization and cross-pathogenically assessment of P. capsici isolate from farm soils in the North Western Himalayan region of India, which has a dynamic virulence profile and distinct host range.

Synthesis of Indolyl Isothiocyanate and Its Inhibitory Activity against Fungi.

Based on previous research, this study synthesized 24 compounds by splicing the substructures of the indolyl group and the isothiocyanate group. Alternaria alternata, Phytophthora capsici, Botrytis cinerea, and Valsa mali were used to test the activity of the target compounds. At 100 μg/mL, compounds 8, 13, 14, and 17 exhibited excellent inhibitory effects of more than 80% on P. capsici, B. cinerea, and V. mail. The EC50 values of compounds 13 and 14 were 0.64 and 2.08 μg/mL, respectively. Potted antifungal activity demonstrated that compounds 13 and 14 had a protective effect of around 80% against B. cinerea at 200 μg/mL. Further physiological and biochemical studies on B. cinerea revealed that compound 13 thickened cell walls and caused mitochondrial vacuolization. Moreover, theoretical calculations indicated that the charge distribution of indolyl isothiocyanate compounds played a crucial role in the observed fungicidal activity. In summary, this study provided fundamental reference data for the derivative synthesis of these indolyl isothiocyanate compounds.

Spontaneously Formed Ratio-Tunable Micro- and Nano-Capsule Coexist System for Precision and on-Demand Fungicide Delivery in Crop Leave.

Multiscale particle size functional pesticide carriers can provide more efficient protection for plants, but this protection is difficult to achieve via single-scale formulation technology. This study presents a novel one-step method for the preparation of lignin-based micro/nanocapsules with controllable proportions within a unified system. This strategy enables the adjustment of the proportion of nanocapsules to between 18.81% and 85.21%. The microcapsules (MCs) vary in diameter from 2 to 3µm, whereas the nanocapsules (NCs) span from 160 to 220nm, with an encapsulation efficiency exceeding 90%. An increased proportion of NCs in the system leads to faster release, heightened sensitivity to UV light, and enhanced penetration into the leaves. During Phytophthora capsici (P. capsici) infection, the NCs in the leaves interact with the defensive enzymes of the plant to quickly respond. Moreover, an optimal balance of MCs and NCs is key to effective fungicide use, not just a higher concentration of NCs. A 65:35 ratio of NCs to MCs ensures effective inhibition of P. capsici outside leaves and a rapid response to leaf invasion. This study enhances fungicide efficiency and advances the development of nanoresponsive fungicides to promote sustainable agricultural practices.

Characterisation of Phytophthora capsici, causal agent of phytophthora foot rot disease of Piper nigrum L. in Sarawak, Malaysia

Phytophthora capsici causes Phytophthora foot rot disease on Piper nigrum. The pathogen lacks comprehensive study in Sarawak, Malaysia. In this study, P. capsici was isolated and characterised morphologically and molecularly from ten farms across three divisions in Sarawak. The pathogenicity of the isolates was confirmed, and distinct colony growth patterns, sporangia morphologies, and radial growth rates were observed across different media. Torulose hyphae structures were consistently observed, and compatible mating types were present. Fifty-two isolates retrieved from this study were genotyped using five Inter Simple Sequence Repeats and three Random Amplified Microsatellites primers. The UPGMA tree showed a close relationship between populations. A higher diversity within populations (73%) than among populations (27%) was observed. This study provides the first baseline data on the diversity of P. capsici in Sarawak, offering insights for managing the disease’s impact on pepper cultivation and the potential risk of increasing genetic diversity.

Dual RNA sequencing during Trichoderma harzianum-Phytophthora capsici interaction reveals multiple biological processes involved in the inhibition and highlights the cell wall as a potential target.

Phytophthora capsici is a destructive oomycete pathogen, causing huge economic losses for agricultural production. The genus Trichoderma represents one of the most extensively researched categories of biocontrol agents, encompassing a diverse array of effective strains. The commercial biocontrol agent Trichoderma harzianum strain T-22 exhibits pronounced biocontrol effects against many plant pathogens, but its activity against P. capsici is not known. T. harzianum T-22 significantly inhibited the growth of P. capsici mycelia and the culture filtrate of T-22 induced lysis of P. capsici zoospores. Electron microscopic analyses indicated that T-22 significantly modulated the ultrastructural composition of P. capsici, with a severe impact on the cell wall integrity. Dual RNA sequencing revealed multiple biological processes involved in the inhibition during the interaction between these two microorganisms. In particular, a marked upregulation of genes was identified in T. harzianum that are implicated in cell wall degradation or disruption. Concurrently, the presence of T. harzianum appeared to potentiate the susceptibility of P. capsici to cell wall biosynthesis inhibitors such as mandipropamid and dimethomorph. Further investigations showed that mandipropamid and dimethomorph could strongly inhibit the growth and development of P. capsici but had no impact on T. harzianum even at high concentrations, demonstrating the feasibility of combining T. harzianum and these cell wall synthesis inhibitors to combat P. capsici. These findings provided enhanced insights into the biocontrol mechanisms against P. capsici with T. harzianum and evidenced compatibility between specific biological and chemical control strategies. © 2024 Society of Chemical Industry.

Synthesis, Anti-Oomycete and Anti-Fungal Activities of Anhydride Derivatives of Oleanolic Acid.

Oleanolic acid is a pentacyclic triterpenoid extracted and isolated from the fruit of plants in the Ligustrum lucidum Ait. in the family Oleaceae. To discover biorational natural product-based pesticides, a series of oleanolic acid derivatives containing anhydride active skeletons were prepared by ingeniously introducing an active acyloxy group at its C-28 carboxyl position, and their structures were well characterized by 1H NMR, 13C NMR, HRMS, and m.p.. The stereochemical configuration of compound 8e was confirmed using single-crystal X-ray diffraction. Furthermore, bioactivities of these compounds as anti-oomycete and anti-fungal agents against two serious agricultural pests, Phytophthora capsici and Fusarium graminearum we assessed. Amongst evaluated compounds, 1) Compounds 8h and 8j displayed significant anti-oomycete against P. capsici, with EC50 values of 54.73 and 65.15 mg/L, respectively. 2) The target compounds have obvious selectivity, and their anti-oomycete activity is significantly better than their anti-fungal activity. 3) Interestingly, there are significant differences in the structure-activity relationship of different substituents or the same substituent at different positions anti-oomycete and anti-fungal against P. capsici and F. graminearum, respectively. The study provides an idea for further exploring the bioactivities of 28-acyloxyoleanolic acid derivatives, and develops the application of 28-acyloxyoleanolic acid derivatives containing anhydride in agriculture.

Characterization of Siderophore Produced by Bacillus velezensis YL2021 and Its Application in Controlling Rice Sheath Blight and Rice Blast.

Bacillus velezensis YL2021 has extensive antimicrobial activities against phytopathogens, and its genome harbors a catechol-type siderophore biosynthesis gene cluster. Here, we describe the characterization of siderophore produced by strain YL2021 and its antimicrobial activity in vitro and in vivo. A few types of siderophores were detected by chrome azurol S plates coupled with Arnow's test, purified and identified by Reversed-phase high-performance liquid chromatography (RP-HPLC). We found that strain YL2021 can produce different antimicrobial compounds under low-iron M9 medium or iron-sufficient LB medium although antimicrobial activities can be easily observed on the two media as described above in vitro. Strain YL2021 can produce at least three catechol-type siderophores in low-iron M9 medium while no siderophore was produced in LB medium. Among them, the main antimicrobial siderophore produced by strain YL2021 was bacillibactin, with m/z of 882, based on the liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis, which has broad-spectrum antimicrobial activities against Gram-positive, Gram-negative bacteria, the oomycete Phytophthora capsici and phytopathogenic fungi. Moreover, the antifungal activity of siderophore including bacillibactin observed in vitro was correlated with control efficacies against rice sheath blight disease caused by Rhizoctonia solani and rice blast disease caused by Magnaporthe oryzae in vivo. Collectively, the results demonstrate that siderophore including bacillibactin produced by Bacillus velezensis YL2021 is a promising biocontrol agent for application in rice disease control.

PcLRR-RK3, an LRR receptor kinase is required for growth and in-planta infection processes in Phytophthora capsici

ABSTRACT Receptor protein kinases (RPKs) critically provide the basic infrastructure to sense, perceive, and conduct the signalling events at the cell surface of organisms. The importance of LRR-RLKs has been well studied in plants, but much less information has been reported in oomycetes. In this work, we have silenced the PcLRR-RK3 and characterised its functional importance in Phytophthora capsici. PcLRR-RK3 was predicted to encode signal peptides, leucine-rich repeats, transmembrane, and kinase domains. PcLRR-RK3-silenced transformants showed impaired colony growth, decreased deformed sporangia, and reduced zoospores count. The mycelium of silenced transformants did not penetrate within the host tissues and showed defects in the pathogenicity of P. capsici. Interestingly, gene silencing also weakens the ability of zoospores germination and penetration into host tissues and fails to produce necrotic lesions. Furthermore, PcLRR-RK3 localisation was found to be the plasma membrane of the cell. Altogether, our results revealed that PcLRR-RK3 was required for the regulation of vegetative growth, zoospores penetration, and establishment into host leaf tissues.

Biological activity and systemic translocation of the new tetrazolyloxime fungicide picarbutrazox against plant-pathogenic oomycetes.

Picarbutrazox is a new tetrazolyloxime fungicide discovered in 2014 by Nippon Soda. It is mostly used to protect against Phytophthora spp. and Pythium spp. However, little is known of its inhibition spectrum, protective and curative activity, and systemic translocation in plants. While picarbutrazox did not show obvious antifungal activity, it exhibited significant activity against oomycetes, including Phytophthora spp., Pythium spp. and Phytopythium spp.. The effective concentration for 50% growth inhibition (EC50) values of picarbutrazox against 16 oomycetes ranged from 3.1 × 10-4 and 7.27 × 10-3 μg mL-1. Furthermore, picarbutrazox could markedly inhibited the mycelial development, sporangia production, zoospore release, and cyst germination of Phytophthora capsici, with EC50 values of 1.34 × 10-3, 1.11 × 10-3, 4.85 × 10-3, and 5.88 × 10-2 μg mL-1, respectively. Additionally, under greenhouse conditions, the protective and curative activities of picarbutrazox at 200 mg L-1 (100%, 41.03%) against the P. capsici infection in peppers were higher than those of the reference fungicide dimethomorph at 200 mg L-1 (77.52%, 36.15%). High-performance liquid chromatography analysis confirmed that picarbutrazox showed excellent systemic translocation in pepper plants. The results showed that picarbutrazox markedly inhibited the important plant oomycete pathogens including Phytophthora spp., Pythium spp. and Phytopythium spp.. It also displayed excellent protective, curative and systemic translocation activity. Picarbutrazox thus has significant potential for preventing and controlling diseases caused by oomycetes. © 2024 Society of Chemical Industry.

Dual actions of chloroinconazide on pepper blight in Capsicum annuum: disruption of Phytophthora capsici mycelium and activation of CaCNGC9-mediated SA signaling.

Pepper blight, caused by Phytophthora capsici, is a devastating disease that seriously threatens pepper production worldwide. With the emergence of resistance in P. capsici against conventional fungicides, there is an urgent need to explore novel alternatives for pepper blight management. This study aims to assess the inhibitory effect of chloroinconazide (CHI), a compound synthesized from tryptophan, against pepper blight, and to explore its potential mechanisms of action. The results demonstrated that CHI effectively targeted P. capsici, disrupting its growth and mycelial structure, which resulted in the release of dissolved intracellular substances. Additionally, CHI significantly inhibited the sporangium formation, zoospores release, and zoospores germination, thereby reducing the re-infection of P. capsici. In contrast, the commercial pesticide methylaxyl only inhibited mycelial growth and had limited effect on re-infection, while azoxystrobin inhibited re-infection but had a weak inhibitory effect on mycelial growth. Furthermore, CHI activated the salicylic acid (SA) signaling pathway-mediated immune response to inhibit P. capsici infection in pepper, with this activation being contingent upon cyclic nucleotide-gated ion channel CaCNGC9. CHI exhibited potent dual inhibitory effects on P. capsici by disrupting mycelial structure and activating the CaCNGC9-mediated SA signaling pathway. These dual mechanisms of action suggested that CHI could serve as a promising alternative chemical fungicide for the effective management of pepper blight, offering a new approach to control this devastating disease. Our findings highlighted the potential of CHI as a sustainable and efficient solution to combat the increasing resistance of P. capsici to conventional fungicides, ensuring better crop protection and yield. © 2024 Society of Chemical Industry.