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Concept: Phytophthora capsici

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ABSTRACT A novel disease resistance inhibitor gene (inhibitor of P. capsici resistance [Ipcr]), found in the chile pepper (Capsicum annuum) variety ‘New Mexico Capsicum Accession 10399’ (NMCA10399), inhibits resistance to Phytophthora capsici but not to other species of Phytophthora. When a highly P. capsici-resistant variety was hybridized with NMCA10399, the resultant F1 populations, when screened, were completely susceptible to P. capsici for root rot and foliar blight disease syndromes, despite the dominance inheritance of P. capsici resistance in chile pepper. The F2 population displayed a 3:13 resistant-to-susceptible (R:S) ratio. The testcross population displayed a 1:1 R:S ratio, and a backcross population to NMCA10399 displayed complete susceptibility. These results demonstrate the presence of a single dominant inhibitor gene affecting P. capsici resistance in chile pepper. Moreover, when lines carrying the Ipcr gene were challenged against six Phytophthora spp., the nonhost resistance was not overcome. Therefore, the Ipcr gene is interfering with host-specific resistance but not the pathogen- or microbe-associated molecular pattern nonhost responses.

Concepts: Plant pathogens and diseases, Capsicum annuum, Capsicum, Chili pepper, Phytophthora capsici, Cayenne pepper, Paprika, Jalapeño

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Phytophthora capsici causes significant loss to pepper production in China and our objective was to investigate the population structure in Gansu province. Between 2007 and 2011, 279 isolates were collected from pepper at 24 locations. Isolates (or subsets) were assessed for simple sequence repeat (SSR) genotype, metalaxyl resistance, mating type, and physiological race using cultivars from the World Vegetable Center (AVRDC) and New Mexico Recombinant Inbred Lines (NMRIL’s). The A1 and A2 mating types were recovered from nine locations and metalaxyl resistant isolates from three locations. A total of 104 isolates tested on the AVRDC panel resolved five physiological races. None of 42 isolates tested on the NMRIL panel caused visible infection. SSR genotyping of 127 isolates revealed 59 unique genotypes with 42 present as singletons and 17 having between 2 and 13 isolates. Isolates with identical genotypes were recovered from multiple sites across multiple years and in many cases had different race types and/or metalaxyl sensitivities. Isolates clustered into three groups with each group having almost exclusively the A1 or A2 mating type. Overall it appears long-lived genetically diverse clonal lineages are dispersed across Gansu, outcrossing is rare, and functionally important variation exists within a clonal framework.

Concepts: DNA, Gene, Genetics, Evolution, Biology, Race, Genotype-phenotype distinction, Phytophthora capsici

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A novel type of water soluble chitosan derivatives (TQCSPX) were synthesized including 3-aminopyridine (TQCSP1) and 3-Amino-4-methylpyridine (TQCSP2). The theoretical structures of TQCSPX were calculated by Gaussian 09 and confirmed by FT-IR,1H NMR,13C NMR, elemental analysis and XRD. The antifungal properties of TQCSPX against Phytophthora capsici (P. capsici), Rhizoctonia solani (R. solani), Fusarium oxysporum (F. oxysporum) and Fusarium solani (F. solani) were evaluated at concentrations ranging from 0.2 mg/mL to 0.8 mg/mL. Antifungal results indicated that the derivatives have significantly enhanced antifungal activity after quaternized compared with the original chitosan (CS). Moreover, TQCSP1 inhibited the growth of P. capsici with inhibitory indices of 91.94% at 0.8 mg/mL. The experimental results demonstrated that the increasing number of the positive charge would improve the antifungal efficiency of chitosan, which may provide a novel direction for the development of fungicides.

Concepts: Electric charge, Fusarium, Fusarium oxysporum, Quaternary ammonium cation, Ammonium, Solution, Plant pathogens and diseases, Phytophthora capsici

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Phytophthora capsici is a devastating oomycete that affects solanaceous, cucurbitaceous, fabaceous, and other crops in the United States (US) and worldwide. The release of the P. capsici genome allows for design of robust markers for genetic studies. We identified and characterized microsatellites in the P. capsici transcriptome. A subset of 50 microsatellites were assayed in a diverse set of P. capsici isolates and evaluated for polymorphism. Polymorphic microsatellites were confirmed by fragment analysis, and 12 were used for population characterization of 50 P. capsici isolates from different states, hosts, and mating types. Analysis of genetic relationship among isolates revealed significant geographic structure by state. Our findings highlight the usefulness of these 12 microsatellites to characterize the population structure of P. capsici and potential transferability to closely-related Phytophthora spp. since markers are located in coding regions. Our markers will facilitate genetic characterization and complement phenotypic studies of P. capsici populations, which may assist in deployment of disease management strategies.

Concepts: Gene, Genetics, Demography, United States, U.S. state, Set, Water moulds, Phytophthora capsici

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Peppers (Capsicum sp.) are an increasingly important crop because of their use as a vegetable, spice, and food colorant. The oomycete Phytophthora capsici is one of the most devastating pathogens to pepper production worldwide, causing more than $100 million in losses annually. Developing cultivars resistant to P. capsici is challenging because of the many physiological races that exist and new races that are continuously evolving. This problem is confounded by the lack of a universal system of race characterization. As a basis to develop a global anticipatory breeding program, New Mexico Recombinant Inbred Lines (NMRILs) functioned as a host differential for Phytophthora root rot to characterize the race structure of P. capsici populations in Taiwan. Using the NMRILs, 24 new races were identified, illustrating the utility and usefulness of the NMRILs for anticipatory breeding. Virulence of P. capsici was observed to be geographically specific and in two virulence clusters. Interestingly, all but two isolates collected in 2016 were the A2 mating type, which is a shift from the predominantly A1 mating type isolates collected prior to 2008. The NMRILs host differential provides an approach for scientists to work together on a global scale when breeding for resistance as well as on a local level for regional gene deployment. Additionally, we propose that the current race numbering system, which has no biological meaning, be supplemented with the virulence phenotype, based on the susceptible NMRILs to a given isolate. This work provides insights into the population dynamics of P. capsici and interactions within the highly complex Capsicum-Phytophthora pathosystem, and offers a basis for similar research in other crops.

Concepts: Biology, Demography, Population, Fungus, United States, Race, Breeding, Phytophthora capsici

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A series of novel pyraclostrobin derivatives were designed and prepared as antifungal agents. Their antifungal activities were tested in vitro with five important phytopathogenic fungi, namely, Batrylis cinerea, Phytophthora capsici, Fusarium sulphureum, Gloeosporium pestis and Sclerotinia sclerotiorum using the mycelium growth inhibition method. Among these compounds, 5s displayed IC50value of 0.57 μg/mL against Batrylis cinerea and 5k-II displayed IC50value of 0.43 μg/mL against Sclerotinia sclerotiorum, which were close to that of the positive control pyraclostrobin (0.18 μg/mL and 0.15 μg/mL). Other compounds 5f, 5k-II, 5j, 5m and 5s also exhibited strong antifungal activity. Further enzymatic assay demonstrated compound 5s inhibited porcine bc1complex with IC50value of 0.95 μM. The statistical results from an integrated computational pipeline demonstrated the predicted total binding free energy for compound 5s is the highest. Consequently, compound 5s with the biphenyl-4-methoxyl side chain could serve as a new motif as inhibitors of bc1complex and deserve to be further investigated.

Concepts: Fungus, Enzyme inhibitor, Enzyme assay, Plant pathogens and diseases, Antifungal drug, Sclerotinia sclerotiorum, Fungicide, Phytophthora capsici

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With the increasing availability of plant pathogen genomes, secreted proteins that aid infection (effectors) have emerged as key factors that help govern plant-microbe interactions. The conserved CRN (CRinkling and Necrosis) effector family was first described in oomycetes by their capacity to induce host cell death. Despite recent advances towards elucidation of CRN virulence functions, the relevance of CRN induced cell death remains unclear. In planta over-expression of PcCRN83_152, a CRN effector from P. capsici, causes host cell death and boosts P. capsici virulence. We used these features to ask whether PcCRN83_152 induced cell death is linked to its virulence function. By randomly mutating this effector, we generated PcCRN83_152 variants with no cell death phenotypes (NCD), which were subsequently tested for activity towards enhanced virulence. We show that a subset of PcCRN83_152 NCD variants retain their ability to boost P. capsici virulence. Moreover, NCD variants were shown to have a suppressive effect on PcCRN83_152 mediated cell death. Our work shows that PcCRN83_152 induced cell death and virulence function can be separated. Moreover, if these findings hold true for other cell death-inducing CRN effectors, this work in turn, will provide a framework for studies aimed at unveiling the virulence functions of these effectors. This article is protected by copyright. All rights reserved.

Concepts: DNA, Gene, Cell, Microbiology, Cell wall, All rights reserved, Copyright, Phytophthora capsici

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The oomycete, Phytophthora capsici, infects cucumber (Cucumis sativus L.) fruit. An age-related resistance (ARR) to this pathogen was previously observed in fruit of cultivar ‘Vlaspik’ and shown to be associated with the peel. Young fruits are highly susceptible, but develop resistance at ~10-12 days post pollination (dpp). Peels from resistant (16 dpp) versus susceptible (8 dpp) age fruit are enriched with genes associated with defense, and methanolic extracts from resistant age peels inhibit pathogen growth. Here we compared developing fruits from ‘Vlaspik’ with those of ‘Gy14’, a line that does not exhibit ARR. Transcriptomic analysis of peels of the two lines at 8 and 16 dpp identified 80 genes that were developmentally upregulated in resistant ‘Vlaspik’ 16 dpp versus 8 dpp, but not in susceptible ‘Gy14’ at 16 dpp. A large number of these genes are annotated to be associated with defense and/or specialized metabolism, including four putative resistance ® genes, and numerous genes involved in flavonoid and terpenoid synthesis and decoration. Untargeted metabolomic analysis was performed on extracts from 8 and 16 dpp ‘Vlaspik’ and ‘Gy14’ fruit peels using Ultra-Performance Liquid Chromatography and Quadrupole Time-of-Flight Mass Spectrometry. Multivariate analysis of the metabolomes identified 113 ions uniquely abundant in resistant ‘Vlaspik’ 16 dpp peel extracts. The most abundant compounds in this group had relative mass defects consistent with terpenoid glycosides. Two of the three most abundant ions were annotated as glycosylated nor-terpenoid esters. Together, these analyses reveal potential mechanisms by which ARR to P. capsici may be conferred.

Concepts: Mass spectrometry, Fruit, Vegetable, Pollination, Time-of-flight, Cucumber, Phytophthora capsici, Cucumis

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Plant-pathogen interactions are complex associations driven by the interplay of host and microbe-encoded factors. With secreted pathogen proteins (effectors) and immune signalling components found in the plant nucleus, this compartment is a battleground where susceptibility is specified. We hypothesized that, by defining changes in the nuclear proteome during infection, we can pinpoint vital components required for immunity or susceptibility. We tested this hypothesis by documenting dynamic changes in the tomato (Solanum lycopersicum) nuclear proteome during infection by the oomycete pathogen Phytophthora capsici. We enriched nuclei from infected and noninfected tissues and quantitatively assessed changes in the nuclear proteome. We then tested the role of candidate regulators in immunity through functional assays. We demonstrated that the host nuclear proteome dynamically changes during P. capsici infection. We observed that known nuclear immunity factors were differentially expressed and, based on this observation, selected a set of candidate regulators that we successfully implicated in immunity to P. capsici. Our work exemplifies a powerful strategy to gain rapid insight into important nuclear processes that underpin complex crop traits such as resistance. We have identified a large set of candidate nuclear factors that may underpin immunity to pathogens in crops.

Concepts: Immune system, Scientific method, Bacteria, Vaccination, Observation, Hypothesis, Water moulds, Phytophthora capsici

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One new indole derivative, chloroindole (1), one new diketone, streptoone A (2), two new ketonic acids, streptoones B (3) and C (4), and one known macrolide antibiotic, X-14952B (5), were isolated from Streptomyces sp. SN0280. Extensive NMR, HRESIMS, and IR analysis was used to elucidate their structures. Streptoone A (2) displayed antibacterial activity (MIC value of 7.81 μg/mL) against Clavibater michiganensis, comparable with the positive control streptomycin (MIC value of 7.81 μg/mL). Streptoone B (3) showed antifungal activity (MIC value of 15.63 μg/mL) against Phytophthora capsici (positive control carbendazol MIC value of 7.81 μg/mL). These molecules provide new templates for the potential treatment and management of these phytopathogens.

Concepts: Bacteria, Microbiology, Erythromycin, Macrolide, Streptomyces, Antibiotics, Phytophthora, Phytophthora capsici