Characteristics of fluopicolide-resistance mutants in Phytophthora nicotianae, the pathogen causing black shank disease in tobacco.

Black shank, a devastating disease in tobacco production worldwide, is caused by the oomycete plant pathogen Phytophthora nicotianae. Fluopicolide is a pyridinylmethyl-benzamides fungicide with a unique mechanism of action and has been widely used for controlling a variety of oomycetes such as Plasmopara viticola, Phytophthora infestans, Pseudoperonospora cubensis, P. nicotianae and Bremia lactucae. However, the fluopicolide-resistance risk and molecular basis in P. nicotianae have not been reported. In this study, the sensitivity profile of 141 P. nicotianae strains to fluopicolide was determined, with a mean median effective concentration (EC50) value of 0.12 ± 0.06µg/mL. Five stable fluopicolide-resistant mutants of P. nicotianae were obtained by fungicide adaptation, and the compound fitness index of these resistant mutants were lower than that of their parental isolates. Additionally, cross-resistance tests indicated that the sensitivity of fluopicolide did not correlate with other oomycete fungicides, apart from fluopimomide. DNA sequencing revealed two point mutations, G765E and N769Y, in the PpVHA-a protein in the fluopicolide-resistant mutants. Transformation and expression of PpVHA-a genes carrying G765E and N769Y in the sensitive wild-type isolate confirmed that it was responsible for fluopicolide resistance. These results suggest that P. nicotianae has a low to medium resistance risk to fluopicolide in laboratory and that point mutations, G765E and N769Y, in PpVHA-a are associated with the observed fluopicolide resistance.

Resistance risk, resistance mechanism and the effect on DON production of a new SDHI fungicide cyclobutrifluram in Fusarium graminearum.

Fusarium head blight in wheat is caused by Fusarium graminearum, resulting in significant yield losses and grain contamination with deoxynivalenol (DON), which poses a potential threat to animal health. Cyclobutrifluram, a newly developed succinate dehydrogenase inhibitor, has shown excellent inhibition of Fusarium spp. However, the resistance risk of F. graminearum to cyclobutrifluram and the molecular mechanism of resistance have not been determined. In this study, we established the average EC50 of a range of F. graminearum isolates to cyclobutrifluram to be 0.0110 µg/mL. Six cyclobutrifluram-resistant mutants were obtained using fungicide adaptation. All mutants exhibited impaired fitness relative to their parental isolates. This was evident from measurements of mycelial growth, conidiation, conidial germination, virulence, and DON production. Interestingly, cyclobutrifluram did not seem to affect the DON production of either the sensitive isolates or the resistant mutants. Furthermore, a positive cross-resistance was observed between cyclobutrifluram and pydiflumetofen. These findings suggest that F. graminearum carries a moderate to high risk of developing resistance to cyclobutrifluram. Additionally, point mutations H248Y in FgSdhB and A73V in FgSdhC1 of F. graminearum were observed in the cyclobutrifluram-resistant mutants. Finally, an overexpression transformation assay and molecular docking indicated that FgSdhBH248Y or FgSdhC1A73V could confer resistance of F. graminearum to cyclobutrifluram.

Two point mutations N771S and K847N in the VHA-a of Phytophthora litchii confer resistance to fluopimomide.

The phytopathogenic oomycete Phytophthora litchii is the culprit behind the devastating disease known as "litchi downy blight", which causes large losses in litchi production. Although fluopimomide exhibits strong inhibitory efficacy against P. litchii, the exact mechanism of resistance is still unknown. The sensitivity of 137 P. litchii isolates to fluopimomide was assessed, and it was discovered that the median effective concentration (EC50) of the fungicide had a unimodal frequency distribution with a mean value of 0.763 ± 0.922 µg/mL. Comparing the resistant mutants to the equivalent parental isolates, the resistance mutants' survival fitness was much lower. While there was no cross-resistance between fluopimomide and other oomycete inhibitors, there is a notable positive cross-resistance between fluopimomide and fluopicolide. According to the thorough investigation, P. litchii had a moderate chance of developing fluopimomide resistance. The point mutations N771S and K847N in the VHA-a of P. litchii (PlVHA-a) were present in the fluopimomide-resistant mutants, and the two point mutations in PlVHA-a conferring fluopimomide resistance were verified by site-directed mutagenesis in the sensitive P. capsici isolate BYA5 and molecular docking.

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 roles in conferring fluopimomide resistance in P. capsici.

Ametoctradin resistance risk and its resistance-related point mutation in PsCytb of Phytophthora sojae confirmed using ectopic overexpression.

Ametoctradin is mainly used to treat plant oomycetes diseases, but the mechanism and resistance risk of ametoctradin in Phytophthora sojae remain unknown. This study determined the ametoctradin sensitivity of 106 P. sojae isolates and found that the frequency distribution of the median effective concentration (EC50) of ametoctradin was unimodal with a mean value of 0.1743 ± 0.0901 µg/mL. Furthermore, ametoctradin-resistant mutants had a substantially lower fitness index compared with that of wild-type isolates. Although ametoctradin did not show cross-resistance to other fungicides, negative cross-resistance to amisulbrom was found. In comparison to sensitive isolates, the control efficacy of ametoctradin to resistant mutants was lower, implying a low to moderate ametoctradin resistance risk in P. sojae. All ametoctradin-resistant mutants contained a S33L point mutation in PsCytb. A system with overexpression of PsCytb in the nucleus was established. When we ectopically overexpressed S33L-harboring PsCytb, P. sojae developed ametoctradin resistance. We hypothesized that the observed negative resistance between ametoctradin and amisulbrom could be attributed to conformational changes in the binding cavity of PsCytb at residues 33 and 220.

Analysis of resistance risk and mechanism of the 14α-demethylation inhibitor ipconazole in Fusarium pseudograminearum.

Ipconazole is a broad-spectrum triazole fungicide that is highly effective against Fusarium pseudograminearum. However, its risk of developing resistance and mechanism are not well understood in F. pseudograminearum. Here, the sensitivities of 101 F. pseudograminearum isolates to ipconazole were investigated, and the average EC50 value was 0.1072 µg/mL. Seven mutants resistant to ipconazole were obtained by fungicide adaption, with all but one showing reduced fitness relative to the parental isolates. Cross-resistance was found between ipconazole and mefentrifluconazole and tebuconazole, but none between ipconazole and pydiflumetofen, carbendazim, fludioxonil, or phenamacril. In summary, these findings suggest that there is a low risk of F. pseudograminearum developing resistance to ipconazole. Additionally, a point mutation, G464S, was seen in FpCYP51B and overexpression of FpCYP51A, FpCYP51B and FpCYP51C was observed in ipconazole-resistant mutants. Assays, including transformation and molecular docking, indicated that G464S conferred ipconazole resistance in F. pseudograminearum.

Resistant risk and resistance mechanism of florylpicoxamid in Colletotrichum gloeosporioides isolated from Chinese walnut.

Colletotrichum gloeosporioides is the causal pathogen for the devastating walnuts anthracnose. A novel quinone inside inhibitor (QiI) fungicide florylpicoxamid has strong inhibitory efficacy against C. gloeosporioides. This study looked into the resistance risk and mechanism of C. gloeosporioides to florylpicoxamid. The basal level sensitivity of C. gloeosporioides isolates (n = 102) to florylpicoxamid was established with an average 50% mycelial growth inhibition concentration (EC50) value of 0.069 ± 0.035 µg/mL. Six stable florylpicoxamid-resistant mutants with resistance factors of >1000 were produced. The fitness of every mutant was much lower than that of their parental isolates. In general, the resistance risk of C. gloeosporioides to florylpicoxamid would be moderate. Molecular docking results revealed that the amino acid substitutions A37V, and S207L in CgCytb lead to a reduction in the binding affinity between florylpicoxamid and CgCytb, indicating that these two mutations (S207L and A37V in CgCytb) indeed confer florylpicoxamid resistance in C. gloeosporioides. These findings offer a fresh viewpoint on the mechanism underlying QiI fungicide resistance and could support the prudent application of florylpicoxamid in the future to combat walnut anthracnose.

Porcine circovirus genotypes and their copathogens in pigs with respiratory disease in southern provinces of Vietnam.

This study was conducted to investigate the genetic diversity of porcine circovirus type 2 (PCV2) and its coinfecting pathogens in pigs with respiratory disease in Vietnam. Samples from 127 clinical cases were obtained from different southern provinces of Vietnam from January 2018 to January 2020 for PCR and sequence analysis. The infection rate of PCV2 was 78.8%, and the major pathogens found in coinfections with PCV2 were porcine reproductive and respiratory syndrome virus, Mycoplasma hyopneumoniae, and Haemophilus parasuis. Forty-three PCV2-positive clinical samples were selected for amplification and sequencing of the ORF2 region. Phylogenetic analysis of PCV2 ORF2 showed that five of the sequences belonged to PCV2b (11.6%) and 38 belonged to PCV2d (88.4%), indicating that PCV2d strains were predominant in southern provinces of Vietnam. Alignment of the predicted amino acid sequences of the PCV2 capsid protein revealed polymorphic sites in the antibody recognition regions. This study demonstrates the prevalence of the PCV2d genotype in southern Vietnam and presents a comprehensive overview of the coinfecting pathogens associated with PCV2 in young pigs with respiratory disease.

Bioactivity of the Novel Fungicide SYP-14288 Against Plant Pathogens and the Study of its Mode of Action Based on Untargeted Metabolomics.

Plant disease is a major threat to crop production, and fungicide application is one of the most effective methods to control plant disease. With emerging issues related to toxic residues and pathogen resistance, new fungicides with novel modes of action are urgently needed. SYP-14288 is a novel fungicide that could efficiently promote respiration and inhibit ATP biosynthesis in target organisms, but its bioactivity against various plant pathogens and exact mode of action are still unknown. In this study, we found that SYP-14288 is highly effective against 31 important plant pathogens belonging to a range of taxonomic groups. In addition, SYP-14288 has demonstrated excellent activity against all life stages of the important fungal plant pathogen Magnaporthe oryzae and is especially effective during the pathogen's high energy consumption stages. SYP-14288 showed good preventative control efficacy against pepper blight and rice blast in the greenhouse and field, respectively. In an untargeted metabolomics assay designed to determine the exact mode of action of SYP-14288, significant changes occurred in 25 metabolites, with the accumulation of seven fatty acid metabolites and a decrease in 18 starch and sugar metabolites (e.g., from the tricarboxylic acid cycle). This suggests that SYP-14288 is an uncoupling agent similar to 2,4-dinitrophenol, which can allow for accumulation of various fatty acids after destroying oxidative phosphorylation coupling, thereby inhibiting the growth of the phytopathogen. These results indicate that the novel uncoupler SYP-14288 is a promising agrochemical in plant disease management.

Use of GC-MS based metabolic fingerprinting for fast exploration of fungicide modes of action.

BACKGROUND: The widespread occurrence of fungicide resistance in fungal plant pathogens requires the development of new compounds with different mode(s) of action (MOA) to avoid cross resistance. This will require a rapid method to identify MOAs. RESULTS: Here, gas chromatography-mass spectrometry (GC-MS) based metabolic fingerprinting was used to elucidate the MOAs of fungicides. Botrytis cinerea, an important pathogen of vegetables and flowers, can be inhibited by a wide range of chemical fungicides with different MOAs. A sensitive strain of B. cinerea was exposed to EC50 concentrations of 13 fungicides with different known MOAs and one with unknown MOA. The mycelial extracts were analyzed for their "metabolic fingerprint" using GC-MS. A comparison among the GC-MS vector' profiles of cultures treated with fungicides were performeded. A model based on hierarchical clustering was established which allowed these antifungal compounds to be distinguished and classified coinciding with their MOAs. Thus, metabolic fingerprinting represents a rapid, convenient, and information-rich method for classifying the MOAs of antifungal substances. The biomarkers of fungicide MOAs were also established by an analysis of variance and included succinate for succinate dehydrogenase inhibitors and cystathionine for methionine synthesis inhibitors. Using the metabolic model and the common perturbation of metabolites, the new fungicide SYP-14288 was identified as having the same MOA as fluazinam. CONCLUSION: This study provides a comprehensive database of the metabolic perturbations of B. cinerea induced by diverse MOA inhibitors and highlights the utility of metabolic fingerprinting for defining MOAs, which will assist in the development and optimization of new fungicides.

Untargeted Metabolomics Based on GC-MS and Chemometrics: A New Tool for the Early Diagnosis of Strawberry Anthracnose Caused by Colletotrichum theobromicola.

To prevent the spread of anthracnose in strawberry plants and characterize the metabolic changes occurring during plant-pathogen interactions, we developed a method for the early diagnosis of disease based on an analysis of the metabolome by gas chromatography-mass spectrometry. An examination of the metabolic profile revealed 189 and 202 total ion chromatogram peaks for the control and inoculated plants, respectively. A partial least squares discriminant analysis (PLS-DA) model was conducted for the reliable and accurate discrimination between healthy and diseased strawberry plants, even in the absence of disease symptoms (e.g., early stages of infection). ANOVA (analysis of variance) and orthogonal partial least squares analysis (OPLS) identified 20 metabolites as tentative biomarkers of Colletotrichum theobromicola infection (e.g., citric acid, d-xylose, erythrose, galactose, gallic acid, malic acid, methyl α-galactopyranoside, phosphate, and shikimic acid). At least some of these potential biomarkers may be applicable for the early diagnosis of anthracnose in strawberry plants. Moreover, these metabolites may be useful for characterizing pathogen infections and plant defense responses. This study confirms the utility of metabolomics research for developing diagnostic tools and clarifying the mechanism underlying plant-pathogen interactions. Furthermore, the data presented herein may be relevant for developing new methods for preventing anthracnose in strawberry seedlings cultivated under field conditions.

Characteristics of famoxadone-resistant mutants of Phytophthora litchii and their effect on lychee fruit quality.

Lychee downy blight (LDB), a common disease caused by the oomycete Phytophthora litchii, poses a significant threat to both pre- and post-harvest stages, leading to substantial economic losses. Famoxadone, a quinone outside inhibitor fungicide, was registered for controlling LDB in China in 2002. However, limited information is available regarding the risk, mechanism, and impact on lychee fruit quality associated with famoxadone resistance. In this study, we determined the sensitivity of 133 P. litchii isolates to famoxadone, yielding a mean EC50 value of 0.46 ± 0.21 µg/mL. Through fungicide adaption, we derived resistant mutants with M124I and Y131C substitutions in PlCyt b (Cytochrome b in P. litchii) from wild-type isolates. In vitro assessments revealed that the fitness of the resistant mutants was significantly lower compared to the parental isolates. These laboratory findings demonstrate a moderate resistance risk of P. litchii to famoxadone. Molecular docking analyses indicated that the M124I and Y131C alterations disrupted hydrogen bonds and weakened the binding energy between famoxadone and PlCyt b. This indicates that the M124I and Y131C changes do indeed confer famoxadone resistance in P. litchii. Infection caused by famoxadone-resistant mutants exhibited a decreased or comparable impact on the characteristic traits of lychee fruit compared to the sensitive isolate. For future detection of famoxadone-resistant strains, AS-PCR primers were designed based on the M124I substitution.

Inhibitory activity to Fusarium spp. and control potential for wheat Fusarium crown rot of a novel succinate dehydrogenase inhibitor cyclobutrifluram.

BACKGROUND: Wheat Fusarium crown rot (FCR) is a serious problem primarily caused by Fusarium pseudograminearum, a pathogenic agent known to produce mycotoxins, including deoxynivalenol (DON). Cyclobutrifluram, a novel succinate dehydrogenase inhibitor devised by Syngenta, has immense potential to control both nematodes and Fusarium diseases. However, its efficacy in combating Fusarium species, its ability to prevent and reverse the detrimental effects of FCR, and its impact on the production of DON by F. pseudograminearum are yet to be fully ascertained. RESULTS: Cyclobutrifluram exhibited substantial inhibitory activity against Fusarium species, with half-maximal effective concentration values ranging from 0.0021-0.0647 µg mL-1 . It demonstrated significant inhibitory activity toward three developmental stages of F. pseudograminearum, F. graminearum and F. asiaticum. Furthermore, cyclobutrifluram showed both protective and curative activities against FCR and was rapidly absorbed by roots and transported to wheat stems and leaves. Cyclobutrifluram could also decrease DON production by F. pseudograminearum. CONCLUSION: This investigation has revealed the potential of cyclobutrifluram as a formidable candidate fungicide, particularly in its ability to effectively combat FCR and other Fusarium-related ailments. This novel compound has exceptional pathogen-fighting capabilities, coupled with remarkable systemic translocation properties and a notable ability to reduce the production of DON. © 2023 Society of Chemical Industry.

Unveiling Vacuolar H+-ATPase Subunit a as the Primary Target of the Pyridinylmethyl-Benzamide Fungicide, Fluopicolide.

An estimated 240 fungicides are presently in use, but the direct targets for the majority remain elusive, constraining fungicide development and efficient resistance monitoring. In this study, we found that Pcα-actinin knockout did not influence the sensitivity of Phytophthora capsici to fluopicolide, which is a notable oomycete inhibitor. Using a combination of Bulk Segregant Analysis Sequencing and Drug Affinity Responsive Target Stability (DARTS) assays, the vacuolar H+-ATPase subunit a (PcVHA-a) was pinpointed as the target protein of fluopicolide. We also confirmed four distinct point mutations in PcVHA-a responsible for fluopicolide resistance in P. capsici through site-directed mutagenesis. Molecular docking, ATPase activity assays, and a DARTS assay suggested a fluopicolide-PcVHA-a interaction. Sequence analysis and further molecular docking validated the specificity of fluopicolide for oomycetes or fish. These findings support the claim that PcVHA-a is the target of fluopicolide, proposing vacuolar H+-ATPase as a promising target for novel fungicide development.

Attributes of Cyazofamid-Resistant Phytophthora litchii Mutants and Its Impact on Quality of Litchi Fruits.

In this study, we determined the sensitivity of 148 Phytophthora litchii isolates to cyazofamid, yielding a mean EC50 value of 0.0091 ± 0.0028 µg/mL. Through fungicide adaptation, resistant mutants (RMs) carrying the F220L substitution in PlCyt b were derived from wild-type isolates. Notably, these RMs exhibited a lower fitness compared with the parental isolates. Molecular docking analysis further revealed that the F220L change contributed to a decrease in the binding energy between cyazofamid and PlCyt b. The total phenol and flavonoid contents in the litchi pericarp treated with cyazofamid on day 5 were significantly higher than in other treatments. Overall, the laboratory assessment indicated a moderate risk of cyazofamid resistance in P. litchii, but the emergence of the F220L change could lead to a high level of resistance. Thus, cyazofamid represents a promising agrochemical for controlling postharvest litchi downy blight and extending the shelf life of litchi fruits.

Novel function of the PsDMAP1 protein in regulating the growth and pathogenicity of Phytophthora sojae.

The DNA methyltransferase 1-associated protein (DMAP1) was initially identified as an activator of DNA methyltransferase 1 (DNMT1), a conserved eukaryotic enzyme involved in diverse molecular processes, including histone acetylation and chromatin remodeling. However, the roles and regulatory mechanisms of DMAP1 in filamentous pathogens are still largely unknown. Here, employing bioinformatic analysis, we identified PsDMAP1 in P. sojae, which features a canonical histone tail-binding domain, as the ortholog of the human DMAP1. A phylogenetic analysis of DMAP1 protein sequences across diverse eukaryotic organisms revealed the remarkable conservation and distinctiveness of oomycete DMAP1 orthologs. Homozygous knockout of PsDMAP1 resulted in the mortality of P. sojae. Furthermore, silencing of PsDMAP1 caused a pronounced reduction in mycelial growth, production of sporangia and zoospore, cystospore germination, and virulence. PsDMAP1 also played a crucial role in the response of P. sojae to reactive oxygen species (ROS) and osmotic stresses. Moreover, PsDMAP1 interacted with DNA N6-methyladenine (6 mA) methyltransferase PsDAMT1, thereby enhancing its catalytic activity and effectively regulating 6 mA abundance in P. sojae. Our findings reveal the functional importance of PsDAMP1 in the development and infection of P. sojae, and this marks the initial exploration of the novel 6 mA regulator PsDMAP1 in plant pathogens.

Uncoupler SYP-14288 inducing multidrug resistance of Phytophthora capsici through overexpression of cytochrome P450 monooxygenases and P-glycoprotein.

BACKGROUND: Fungicide resistance has become a serious problem for different mode of action groups except for uncouplers, which makes their resistance mechanism a hot topic, which until now, has not been well clarified. SYP-14288, a newly developed diarylamine fungicide modeled on fluazinam, has shown good toxicity to both oomycete and fungus by the action of uncoupling. In this research, the resistance of Phytophthora capsici to SYP-14288 was studied to clarify the resistance mechanism of uncouplers. RESULTS: The toxicity tests of resistant strains against SYP-14288 showed multidrug resistance. The high-performance liquid chromatography (HPLC) results showed that resistant strains could efflux the fungicide, and this ability could be inhibited by the efflux pump inhibitor amitriptyline. The target protein of amitriptyline is P-glycoprotein (P-gp), which was overexpressed in resistant strains. Three products of nitrate reduction of SYP-14288 were detected and determined by HPLC-Q-TOF. Eight cytochrome P450 monooxygenase (P450) proteins were differentially involved in the reduction reaction. CONCLUSION: Both fungicide efflux and detoxification metabolism were involved in the resistance mechanisms of P. capsici to SYP-14288. © 2022 Society of Chemical Industry.

Cytochrome P450 and Glutathione S-Transferase Confer Metabolic Resistance to SYP-14288 and Multi-Drug Resistance in Rhizoctonia solani.

SYP-14288 is a fungicide as an uncoupler of oxidative phosphorylation, which is effective in controlling fungal pathogens like Rhizoctonia solani. To determine whether R. solani can develop SYP-14288 resistance and possibly multi-drug resistance (MDR), an SYP-14288-resistant mutant of R. solani X19-7 was generated from wild-type strain X19, and the mechanism of resistance was studied through metabolic and genetic assays. From metabolites of R. solani treated with SYP-14288, three compounds including M1, M2, and M3 were identified according to UPLC-MS/MS analysis, and M1 accumulated faster than M2 and M3 in X19-7. When X19-7 was treated by glutathione-S-transferase (GST) inhibitor diethyl maleate (DEM) and SYP-14288 together, or by DEM plus one of tested fungicides that have different modes of action, a synergistic activity of resistance occurred, implying that GSTs promoted metabolic resistance against SYP-14288 and therefore led to MDR. By comparing RNA sequences between X19-7 and X19, six cytochrome P450s (P450s) and two GST genes were selected as a target, which showed a higher expression in X19-7 than X19 both before and after the exposure to SYP-14288. Furthermore, heterologous expression of P450 and GST genes in yeast was conducted to confirm genes involved in metabolic resistance. In results, the P450 gene AG1IA_05136 and GST gene AG1IA_07383 were related to fungal resistance to multiple fungicides including SYP-14288, fluazinam, chlorothalonil, and difenoconazole. It was the first report that metabolic resistance of R. solani to uncouplers was associated with P450 and GST genes.

PcCesA1 is involved in the polar growth, cellulose synthesis, and glycosidic linkage crosslinking in the cell wall of Phytophthora capsici.

Phytophthora capsici is a destructive plant pathogen that infects a wide range of hosts worldwide. The P. capsici cell wall, rich in cellulose, is vital for hyphal growth and host interactions. However, the enzymes involved in its synthesis remain largely unelucidated. In the current study, we functionally characterized the cellulose synthase gene PcCesA1, which is highly conserved in Phytophthora. By using CRISPR/Cas9-mediated gene replacement and in situ complementation system, it was found PcCesA1 is essential for the mycelial growth, cystospore germination, and pathogenicity of P. capsici. The normal deposition of newly synthesized cell wall components and the polar growth point formation were disrupted in PcCesA1 knockout mutants, suggesting that PcCesA1 plays an important role in the polar growth of P. capsici. Compared with the wild-type strains, PcCesA1 knockout mutants displayed a thicker inner layer cell wall and were more sensitive to carboxylic acid amide fungicides (CAAs). The contents of the cell wall polysaccharides 1,4-Glc, 1,4,6-Glc, and 1,3,4-Glc were reduced in PcCesA1 knockout mutants, suggesting that PcCesA1 affected cellulose content and glycosidic linkage crosslinking in the cell wall. Our findings demonstrate that PcCesA1 is required for cell wall biogenesis. Therefore, PcCesA1 may be a potential target for Phytophthora disease control.

Metabolic Mechanism of Plant Defense against Rice Blast Induced by Probenazole.

The probenazole fungicide is used for controlling rice blast (Magnaporthe grisea) primarily by inducing disease resistance of the plant. To investigate the mechanism of induced plant defense, rice seedlings were treated with probenazole at 15 days post emergence, and non-treated plants were used for the control. The plants were infected with M. grisea 5 days after chemical treatment and incubated in a greenhouse. After 7 days, rice seedlings were sampled. The metabolome of rice seedlings was chemically extracted and analyzed using gas chromatography and mass spectrum (GC-MS). The GC-MS data were processed using analysis of variance (ANOVA), principal component analysis (PCA) and metabolic pathway elucidation. Results showed that probenazole application significantly affected the metabolic profile of rice seedlings, and the effect was proportionally leveraged with the increase of probenazole concentration. Probenazole resulted in a change of 54 metabolites. Salicylic acid, γ-aminobutyrate, shikimate and several other primary metabolites related to plant resistance were significantly up-regulated and some metabolites such as phenylalanine, valine and proline were down-regulated in probenazole-treated seedlings. These results revealed a metabolic pathway of rice seedlings induced by probenazole treatment regarding the resistance to M. grisea infection.