Phytophthora Blight Of Pepper Research Articles

CaWRKY01-10 and CaWRKY08-4 Confer Pepper's Resistance to Phytophthora capsici Infection by Directly Activating a Cluster of Defense-Related Genes.

Phytophthora blight of pepper, which is caused by the notorious oomycete pathogen Phytophthora capsici, is a serious disease in global pepper production regions. Our previous study had identified two WRKY transcription factors (TFs), CaWRKY01-10 and CaWRKY08-4, which are prominent modulators in the resistant pepper line CM334 against P. capsici infection. However, their functional mechanisms and underlying signaling networks remain unknown. Herein, we determined that CaWRKY01-10 and CaWRKY08-4 are localized in plant nuclei. Transient overexpression assays indicated that both CaWRKY01-10 and CaWRKY08-4 act as positive regulators in pepper resistance to P. capsici. Besides, the stable overexpression of CaWRKY01-10 and CaWRKY08-4 in transgenic Nicotiana benthamiana plants also significantly enhanced the resistance to P. capsici. Using comprehensive approaches including RNA-seq, CUT&RUN-qPCR, and dual-luciferase reporter assays, we revealed that overexpression of CaWRKY01-10 and CaWRKY08-4 can activate the expressions of the same four Capsicum annuum defense-related genes (one PR1, two PR4, and one pathogen-related gene) by directly binding to their promoters. However, we did not observe protein-protein interactions and transcriptional amplification/inhibition effects of their shared target genes when coexpressing these two WRKY TFs. In conclusion, these data suggest that both of the resistant line specific upregulated WRKY TFs (CaWRKY01-10 and CaWRKY08-4) can confer pepper's resistance to P. capsici infection by directly activating a cluster of defense-related genes and are potentially useful for genetic improvement against Phytophthora blight of pepper and other crops.

Evaluation of a Formulation of Bacillus subtilis for Control of Phytophthora Blight of Bell Pepper.

Phytophthora blight, caused by Phytophthora capsici, is one of the most economically significant diseases of bell pepper in the United States. Over the past several decades, isolates of P. capsici exhibiting resistance to mefenoxam and other fungicides have been reported. Fungicide resistance coupled with an increased market for organically grown crops has led to interest in biological control as a disease management option. In this work, an isolate of Bacillus subtilis (AFS032321) was evaluated for control of Phytophthora blight of bell pepper in the greenhouse and field. A 28% active ingredient wettable powder formulation of the strain was applied as a soil drench at transplanting prior to inoculation. Treatment with this formulation of B. subtilis significantly reduced the area under the disease progress curve (AUDPC) by up to 52% compared to untreated control plants in greenhouse tests. Comparisons between applying the biocontrol weekly after seeding for 5 weeks versus a single application at transplanting (5 weeks) indicated no significant benefits of additional applications. The formulation of B. subtilis reduced disease caused by a mefenoxam-resistant isolate of P. capsici, while mefenoxam failed. The biocontrol efficacy of formulated strains was not affected in different soil types or potting media. However, disease was more severe in sandy soils. In field experiments that were conducted with a mefenoxam-sensitive isolate, disease incidence and severity of Phytophthora blight were significantly reduced at all rates of B. subtilis in 2019 except the 16.8 kg ha-1 rate. In both years, mefenoxam was more effective than B. subtilis in controlling disease in the field. B. subtilis did not affect the spatial dynamics of pathogen spread within rows. While the precise mechanism(s) of action is unclear, in vitro dual-culture tests suggest direct antagonism, as B. subtilis significantly inhibited colony growth of P. capsici. AgBiome has recently released a new formulation of the AFS032321 strain named Theia, with higher active ingredients for commercial applications and biocontrol of P. capsici.

Integrative Transcriptome Analysis of mRNA and miRNA in Pepper's Response to Phytophthora capsici Infection.

Phytophthora blight of pepper is a notorious disease caused by the oomycete pathogen Phytophthora capsici, which poses a great threat to global pepper production. MicroRNA (miRNA) is a class of non-coding small RNAs that regulate gene expressions by altering the translation efficiency or stability of targeted mRNAs, which play important roles in the regulation of a plant's response to pathogens. Herein, time-series mRNA-seq libraries and small RNA-seq libraries were constructed using pepper roots from the resistant line CM334 and the susceptible line EC01 inoculated with P. capsici at 0, 6, 24, and 48 h post-inoculation, respectively. For mRNA-seq analysis, a total of 2159 and 2971 differentially expressed genes (DEGs) were identified in CM334 and EC01, respectively. For miRNA-seq analysis, 491 pepper miRNAs were identified, including 330 known miRNAs and 161 novel miRNAs. Among them, 69 and 88 differentially expressed miRNAs (DEMs) were identified in CM334 and EC01, respectively. Examination of DEMs and their targets revealed 22 regulatory networks, predominantly featuring up-regulated miRNAs corresponding to down-regulated target genes. Notably, these DEM-DEG regulatory networks exhibited significant overlap between CM334 and EC01, suggesting that they might contribute to pepper's basal defense against P. capsici. Furthermore, five selected DEMs (miR166, miR1171, miR395, miR530 and miRN2) and their target genes underwent qRT-PCR validation, confirming a consistent negative correlation in the expression patterns of miRNAs and their targets. This comprehensive analysis provides novel insights into the regulatory networks of miRNAs and their targets, offering valuable contributions to our understanding of pepper's defense mechanisms against P. capsici.

Identification of Lydicamycins as Main Antioomycete Compounds from the Biocontrol Agent Streptomyces sp. NEAU-S7GS2.

Oomycetes are well-known phytopathogens that seriously threaten many important crops worldwide. In this study, the endophytic actinobacterium Streptomyces sp. NEAU-S7GS2 demonstrated significant antagonistic activity against Phytophthora and Pythium and showed a potent biocontrol effect on suppression of soybean phytophthora root rot and pepper phytophthora blight. Two compounds were subsequently isolated as the main active components by bioassay-guided fractionation and identified as lydicamycins A and B. These two compounds showed high antioomycete activity against Phytophthora and Pythium with EC50 values of 0.73-2.67 μg/mL, which are equal to or lower than those of commercialized drug metalaxyl. In vivo bioassay using detached leaves demonstrated that lydicamycin A had a better control efficiency against soybean phytophthora root rot than metalaxyl. Taken together, these results suggest that the biocontrol agent Streptomyces sp. NEAU-S7GS2 and lydicamycins have the potential to be developed as promising pesticides to control diseases caused by oomycetes.

Controlling Phytophthora blight of pepper in Guizhou Province of China using Stellera chamaejasme extracts and synthetic chemical fungicides

Controlling Phytophthora blight of pepper in Guizhou Province of China using Stellera chamaejasme extracts and synthetic chemical fungicides

Screening of Streptomyces strains helping arbuscular mycorrhizal symbiosis against pepper (Capsicum annuum L.) Phytophthora blight

Mycorrhiza helper bacteria (MHB) can promote the formation and functioning of arbuscular mycorrhizal (AM) symbiosis, but their role and application potential in coping with soil-borne diseases are still unclear. The aim of this 14-week greenhouse pot experiment was to obtain several actinomycetes strains which could help AM symbiosis in suppressing the Phytophthora blight of pepper (Capsicum annuum L.), using a soil inoculated with Phytophthora capsici after sterilization. Five Streptomyces strains, including S. pseudogriseolus, S. albogriseolus, S. griseoaurantiacus, S. tricolor and S. tendae, as well as the AM fungus (Funneliformis caledonium) were tested. The Phytophthora blight severity reached 66% at full productive stage in the control, and only F. caledonium, S. griseoaurantiacus and S. tricolor alone remarkably decreased (P < 0.05) it to 47%, 40%, and 35%, respectively. Compared to F. caledonium alone, only additional inoculation of S. tricolor and S. tendae which were isolated from the rhizosphere of a healthy individual in an infected field substantially elevated (P < 0.05) root mycorrhizal colonization, root biomass, fruit yield, and total K acquisitions of pepper, and further dramatically decreased (P < 0.05) the severity. According to the feature of enhancing disease-suppression by AM symbiosis, both S. tricolor and S. tendae were confirmed as MHB strains here. Specifically, S. tendae had a stronger performance in directly accelerating mycorrhization, while S. tricolor was also an antagonist to the pathogenic P. capsici. Furthermore, S. griseoaurantiacus with the independent disease-suppression function was not a MHB strain here. The redundancy analyses demonstrated that when AM fungus present, root mycorrhizal colonization replaced soil pH becoming the main factor impacting pepper Phytophthora blight. Thus, S. tricolor and S. tendae seemed to have the value of preparation and application in the future to help AM symbiosis against pepper Phytophthora blight.

Triphenylphosphonium-Driven Targeting of Pyrimorph Fragment Derivatives Greatly Improved Its Action on Phytopathogen Mitochondria.

Pyrimorph is a carboxylic acid amide (CAA) fungicide, which shows excellent activity against oomycetes such as pepper phytophthora blight, tomato late blight, and downy mildew of cucumber. It works mainly by inhibiting the biosynthesis of cell wall of oomycetes. However, pyrimorph also shows weak activity of inhibiting mitochondrial complex III, which is the first CAA fungicide found to act on mitochondria. To improve this effect on mitochondria and develop fungicides that may have a novel mechanism of action, in this paper, by disassembling pyrimorph and conjugating the fragments with the mitochondrial-targeted delivery system (triphenylphosphonium), three series of mitochondrial-targeting analogues of pyrimorph were designed and synthesized. The results show that the pyridine-containing 1,1-diaryl is the core module of inhibition mitochondrial function of pyrimorph. Among these conjugates, compound 3b with a short linker showed the highest and broad-spectrum fungicidal activity, strong respiratory inhibition activity, and adenosine 5'-triphosphate synthesis inhibition activity, suggesting its potential as a fungicide candidate. 3b exhibited greatly improved action on mitochondria, such as by destroying the mitochondrial function of pathogens, causing mitochondrial swelling, weakening its influence on cell wall morphology, and so on. More importantly, this study provides a method to strengthen the drugs or pesticides with weak mitochondrial action, which is of special significance for developing mitochondrial bioactive molecules with the novel action mechanism.

Anti-Oomycete Activity and Pepper Root Colonization of Pseudomonas plecoglossicida YJR13 and Pseudomonas putida YJR92 against Phytophthora capsici

Previously, Pseudomonas plecoglossicida YJR13 and Pseudomonas putida YJR92 from a sequential screening procedure were proven to effectively control Phytophthora blight caused by Phytophthora capsici. In this study, we further investigated the anti-oomycete activities of these strains against mycelial growth, zoospore germination, and germ tube elongation of P. capsici. We also investigated root colonization ability of the bacterial strains in square dishes, including cell motility (swimming and swarming motilities) and biofilm formation. Both strains significantly inhibited mycelial growth in liquid and solid V8 juice media and M9 minimal media, zoospore germination, and germ tube elongation compared with Bacillus vallismortis EXTN-1 (positive biocontrol strain), Sphingomonas aquatilis KU408 (negative biocontrol strain), and MgSO4 solution (untreated control). In diluted (nutrient-deficient) V8 juice broth, the tested strain populations were maintained at >108 cells/ml, simultaneously providing mycelial inhibitory activity. Additionally, these strains colonized pepper roots at a 106 cells/ml concentration for 7 days. The root colonization of the strains was supported by strong swimming and swarming activities, biofilm formation, and chemotactic activity towards exudate components (amino acids, organic acids, and sugars) of pepper roots. Collectively, these results suggest that strains YJR13 and YJR92 can effectively suppress Phytophthora blight of pepper through direct anti-oomycete activities against mycelial growth, zoospore germination and germ tube elongation. Bacterial colonization of pepper roots may be mediated by cell motility and biofilm formation together with chemotaxis to root exudates.

Degradation of soil arbuscular mycorrhizal fungal diversity and functionality accompanied by the aggravation of pepper Phytophthora blight in a facility shed in Southwest China

AbstractArbuscular mycorrhizal (AM) fungi play a vital role in plant's resistance against soil‐borne pathogens including Phytophthora capsici, which causes the devastating Phytophthora blight and threatens pepper (Capsicum annuum L.) cultivation worldwide. In order to understand the interaction of indigenous AM fungal community and P. capsici during the aggravation of Phytophthora blight, a survey was performed in a facility shed in Southwest China. The blight severity of pepper plants was evaluated based on a 0–5 scale (L0–L5), and the corresponding root AM fungal colonization, and the abundance and community composition of AM fungi as well as the population of P. capsici in root‐adjacent soil, were all investigated. Along with the rise of disease severity, increased soil P. capsici population was shown. In contrast, there were significant decreases in root colonization rate and the diversity indices rather than the abundance of soil AM fungi. The root colonization rate and the diversity indices of AM fungi all showed significant negative correlations with soil P. capsici population. Compared to plants with lower disease severities (L0–L2), higher severities (L3–L5) significantly modified soil AM fungal community composition, mainly through replacing the beneficial Glomus phylotypes by Paraglomus ones. Overall, the results disclosed the dynamic competition between indigenous AM fungi and P. capsici behind the onset of pepper Phytophthora blight, which highlights the importance of establishing soil suppressiveness on the control of soil‐borne diseases.

Discovery of febrifugine with specific anti-Phytophthora oomycete activity isolated from Dichroa febrifuga Lour

Dichroa febrifuga has been used in traditional Chinese medicine for centuries to treat productive cough and fevers caused by malaria infection, however the antimicrobial activity is still unknown. In this study, the crude alkaloids extract of D. febrifuga leaves showed potent anti-oomycete activity against phytopathogen Phytophthora capsici. Subsequent bioassay-guided fractionation led to identify febrifugine as the main active component. Febrifugine showed specific in vitro anti-oomycete activity against P. capsici, Phytophthora sojae and Phytophthora infestans with EC50 of 1.741, 1.674 and 0.413 μg/mL, respectively, but showed no or weak antifungal activity against twelve test phytopathogenic fungi. Scanning electron microscope and optical microscope results indicated that febrifugine could alter the morphology of P. infestans hyphae, but did not destroy the cell wall. The electrical conductivity and intracellular component leakage experiments suggested the integrity of the cell membrane after the treatment of febrifugine. Moreover, febrifugine possessed inhibitory effects on zoospore release and germination of P. infestans. In vivo bioassay using detached leaves demonstrated that febrifugine had better protective and curing activities than commercialized drug metalaxyl. The application of febrifugine at a dose of 60 μg/mL provided protective efficacies of 93.1% and 91.9%, and curing efficacies of 86.2% and 86.6% for pepper phytophthora blight and potato late blight, respectively. Taken together, this study showed that the crude alkaloids extract of D. febrifuga and its active component febrifugine represent alternatives to control plant diseases caused by oomycetes, and febrifugine is expected to be a new leading structure for the development of oomyceticides.

The defense response of pepper (Capsicum annuum L.) induced by exopolysaccharide from Schizophyllum commune

β-glucan, a major cell wall component of fungal species, functions as an elicitor inducing plant defense activities. The exopolysaccharide from Schizophyllum commune HNU-12 (SC-EP) showed a protective effect on pepper against Phytophthora blight disease. Quantitative real-time PCR revealed that the expression of defense genes, CaBPR1, CaBGLU and CaPR-4 was significantly induced in SC-EP and dl-β-aminobutyric acid-treated pepper leaves. Furthermore, phenolic compounds, phenylalanine ammonia lyase activity and salicylic acid contents increased in SC-EP-treated pepper leaves. Our findings indicate that SC-EP can be used as an elicitor to induce defense activities against Phytophthora blight of pepper.

Anti-fungal activity of moso bamboo (Phyllostachys pubescens) leaf extract and its development into a botanical fungicide to control pepper phytophthora blight

Moso bamboo (Phyllostachys pubescens, Gramineae) is a well-known medicinal and edible plant found in China with various bioactivities, but few systematic studies address the utilization of its anti-fungal activity. The extract of moso bamboo leaf showed good anti-fungal activity to Phytophthora capsici, Fusarium graminearum, Valsa mali Miyabe et Yamada, Botryosphaeria dothidea, Venturia nashicola, and Botrytis cinerea Pers, with inhibitory rate of 100.00%, 75.12%, 60.66%, 57.24%, 44.62%, and 30.16%, respectively. Anti-fungal activity was different by the difference of samples picking time and location. The extract showed good synergistic effects with carbendazim at the ratios of 9:1 and 15:1 (extract : carbendazim), and the co-toxicity coefficients were 124.4 and 139.95. Compound 2 was isolated and identified as the main active component, with the EC50 value of 11.02 mg L−1. Then, the extract was formulated as a 10% emulsion in water, which was stable and had no acute toxic effects. Moreover, a field trial about this formulation was assayed to control pepper phytophthora blight, with the control effect of 85.60%. These data provided a better understanding of the anti-fungal activity and relevant active component of moso bamboo leaf extract. Taken together, our findings illustrated that bamboo leaf extract could be developed and utilized as a botanical fungicide or fungicide adjuvant.

Field Validation of PBcast in Timing Fungicide Sprays to Control Phytophthora Blight of Chili Pepper

Field validation of PBcast, an infection risk model for Phytophthora blight of pepper, was conducted through a designed field experiment in 2012 and 2013. Conduciveness of weather conditions at 26 locations in Korea in 2014-2017 was also evaluated using PBcast. The PBcast estimated daily infection risk (IR) of Phytophthora capsici based on weather and soil texture data. In the designed filed experiment, four treatments including routine sprays at 7-day intervals (RTN7), forecast-based sprays when IR reached 200 (IR200) and 224 (IR224), and no spray (CTRL) were compared in terms of disease incidence and number of sprays recommended for disease control. In 2012, IR had reached over 200 twice, but never reached 224. In 2013, IR had reached over 200 three times and once higher than 224. The RTN7 plots were sprayed 17 and 18 times in 2012 and 2013, respectively. Weather conditions throughout the country were generally conducive for Phytophthora blight and 3-4 times of fungicide sprays would have been reduced if the PBcast forecast information was adopted in the decision-making for fungicide sprays. In conclusion, the PBcast forecast would be useful to reduce fungicide applications without losing the disease control efficacy to protect pepper crop from Phytophthora blight.

Discovery of γ-Lactam Alkaloid Derivatives as Potential Fungicidal Agents Targeting Steroid Biosynthesis.

Biological control of plant pathogens is considered as one of the green and effective technologies using beneficial microorganisms or microbial secondary metabolites against plant diseases, and so microbial natural products have played important roles in the research and development of new and green agrochemicals. To explore the potential applications for natural γ-lactam alkaloids and their derivatives, 26 γ-lactams that have flexible substituent patterns were synthesized and characterized, and their in vitro antifungal activities against eight kinds of plant pathogens belonging to oomycetes, basidiomycetes, and deuteromycetes were fully evaluated. In addition, the high potential compounds were further tested using an in vivo assay against Phytophthora blight of pepper to verify a practical application for controlling oomycete diseases. The potential modes of action for compound D1 against Phytophthora capsici were also investigated using microscopic technology (optical microscopy, scanning electron microscopy, and transmission electron microscopy) and label-free quantitative proteomics analysis. The results demonstrated that compound D1 may be a potential novel fungicidal agent against oomycete diseases (EC50 = 4.9748 μg·mL-1 for P. capsici and EC50 = 5.1602 μg·mL-1 for Pythium aphanidermatum) that can act on steroid biosynthesis, which can provide a certain theoretical basis for the development of natural lactam derivatives as potential antifungal agents.

Burkholderia sp. SSG is a broad-spectrum antagonist against plant diseases caused by diverse pathogens

SSG, a Burkholderia isolate recovered from boxwood leaves, has many genes and gene clusters coding plant growth promoting traits and antagonistic activity against plant pathogens. It has been demonstrated that this bacterial isolate is a potent biofertilizer for boxwood and an effective biocontrol agent against boxwood blight. In this study we evaluated SSG against 21 additional pathogens including six bacteria, nine fungi and six Phytophthora species using dual culture assays, and against twelve diseases in planta under controlled environment. SSG suppressed all fungal and Phytophthora species, and five of the six Gram negative bacteria in dual culture. SSG provided the most consistent control to bacterial blight of geranium caused by Xanthomonas campestriscampestriscampestriscampestris at 41% to 58%, and to pansy leaf spot by Colletotrichum fructicola at 30% to 32% across all three treatment timings from 1 day before inoculation (dbi) to 3 days after inoculation (dai). Among the six other diseases evaluated for multiple treatment timings, SSG provided the greatest control at 1 dbi to two diseases with hydrangea anthracnose by C. gloeosporioides at 67% and rhododendron Ramorum blight by Phytophhtora ramorum at 54%. The best SSG control of pansy gray mold by Botrytis cinerea was 67% at 1 wbi while that of tomato spotted wilt virus of impatiens was 53% at 2 wbi. When plants were treated with SSG only at one timing of 1 dbi, the best disease control was observed on Phytophthora blight of annual vinca by P. nicotianae at 95%, followed by pansy leaf spot by Alternaria tenuissima at 60%, Phytophthora blight of bell pepper by P. capsici at 56%, and Volutella blight of boxwood by Pseudonectria rouselliana at 44%. Further investigations into its efficacy for control of two root/crown rot diseases are warranted. Nevertheless, this study demonstrates that SSG is a promising broad-spectrum biocontrol agent for a variety of plant diseases caused by diverse pathogens.

Evaluation of the effectiveness of antagonistic bacteria against Phytophthora blight disease in pepper with artificial intelligence

Phytophthora blight of pepper, caused by Phytophthora capsici, is a disease seriously affects pepper production. The aims of this study were to evaluate the control of P. capsici by antagonistic bacteria in pot trials and to score disease severity by using artificial intelligence (AI). For this purpose, six P. capsici isolates used in the study were identified with PCR, and pathogenicity tests were performed. Biological control pot trials were conducted by testing three antagonistic bacteria. At the end of the pot trials, the disease severity in the plants was rated visually. An AI system was also created for the current study. The scores from the AI system were compared with the visual scale scores with different methods. All pathogen isolates were identified as P. capsici according to the PCR results. PcU5 was found to be the most aggressive isolate of the tested P. capsici isolates according to pathogenicity tests, with 45 mm lesion length. Pca17 was found to be an effective bacterial antagonist, with 77% efficiency in pot trials. The AI system, called PhytAi (https://phytai.online), significantly correctly scored the disease severity when compared with the visual scores (r2 = 0.96). PhytAi can be used not only by phytopathologists but also by any researcher working in plant sciences who needs visual classification. This is a general classification system that supports scale ratings; the determination of varieties, disease severity measurement, and all kinds of visual classification, identification, etc. can be easily performed without changes in the system thanks to AI.

Biochar-Mediated Control of Phytophthora Blight of Pepper Is Closely Related to the Improvement of the Rhizosphere Fungal Community.

Biochar is a new eco-material with the potential to control soilborne diseases. This study explored the relationship between the rhizosphere fungal community and the suppression of Phytophthora blight of pepper in the context of time after biochar application. A pot experiment was conducted and rhizosphere soils were sampled to determine the biochar-induced soil chemical properties, fungal community composition, and abundance of biocontrol fungi. The biochar-enriched fungal strains were screened by the selective isolation method, and their control effects against Phytophthora blight of pepper were determined using a pot experiment. Biochar treatments effectively inhibited pathogen growth and controlled the disease, with biochar applied immediately before planting (BC0) having greater effects than that applied 20 days before planting (BC20). Compared to the control, biochar-amended rhizosphere soils had a higher pH, available nutrient content, and fungal richness and diversity. Moreover, biochar treatments significantly increased the abundance of potential biocontrol fungi. The proliferation in BC0 was stronger as compared to that in BC20. Several strains belonging to Aspergillus, Chaetomium, and Trichoderma, which were enriched by biochar amendment, demonstrated effective control of Phytophthora blight of pepper. Canonical correspondence and Pearson’s correlation analysis showed that a high content of soil-available nutrients in biochar treatments was favorable to the proliferation of beneficial fungi, which was negatively correlated with both the abundance of Phytophthora capsici and disease severity. In conclusion, biochar-mediated improvement in the fungal community suppressed the Phytophthora blight of pepper. The biochar application time had a great impact on the control effect, possibly due to the short-term proliferative effect of the biochar on biocontrol fungi.

Biological control of Phytophthora blight and growth promotion in sweet pepper by Bacillus species

Phytophthora capsici is one of the most important pathogens impacting the production of horticultural crops including pepper (Capsicum annuum). Pepper growers rely heavily on pesticides, but toxicity hazards to farm-workers, consumers, non-target organisms as well as environmental contamination cause great concern. Furthermore, the development of pesticide resistance is problematic. The objective of this study was to evaluate isolates of three Bacillus spp. [B. vallismortis (Ps), B. amyloliquefaciens (PsL) and B. thuringiensis (IMC8)] as biological control agents for P. capsici disease management. These isolates inhibited P. capsici mycelial growth invitro and reduced P. capsici disease severity in plants grown in Phytophthora-infested soil in greenhouse environment. In addition, the three bacterial isolates promoted plant growth by increasing plant height, shoot weight, root length, root weight and chlorophyll content. Out of the three isolates, PsL displayed the best potential in reducing P. capsici disease severity and in promoting plant growth in Phytophthora-infested soil and both PsL and Ps were significantly better than the fungicide metalaxyl (Ridomil®, Syngenta, Greensboro, NC) in reducing disease severity and promoting plant growth in greenhouse environment. In addition, mixtures of IMC8 + Ps, IMC8 + PsL and IMC8 + Ps + PsL reduced P. capsici disease severity and promoted plant growth similar to the fungicide metalaxyl used at label recommended rates. These three isolates IMC8, Ps and PsL displayed potential as alternative products for disease management and C. annuum plant growth promotion.

Growth-promoting and disease-suppressing effects of Paenibacillus polymyxa strain YCP16-23 on pepper (Capsicum annuum) plants

Phytophthora blight is the most devastating disease for pepper (Capsicum annuum L.) production and is caused by Phytophthora capsici. Current management strategies are not effective. Our study assessed the multi-trait effects of Paenibacillus polymyxa, which suppresses Phytophthora blight and promotes plant growth in pepper plants. A total of 82 bacterial strains isolated from rhizosphere soil of pepper plants were screened for in vitro inhibition of P. capsici growth. The results revealed that only six strains showed strong antagonistic activity against P. capsici. These six strains were used for controlling Phytophthora blight in pepper by seedling assays under greenhouse conditions. Three strains showed a lower incidence of Phytophthora blight and were used in further growth-promoting and biocontrol studies under greenhouse conditions. Strain YCP16-23 showed >60.0% suppression of P. capsici and significantly promoted growth of pepper plants compared to the untreated control. Based on cultural and morphological characterization and 16S rRNA gene sequencing, strain YCP16-23 was identified as Paenibacillus polymyxa. Strain YCP16-23 demonstrated many characteristics that are beneficial for plants, such as production of α-amylase, ammonia, cellulase, indole-3-acetic acid, pectinase, siderophores, and protease, as well as solubilization of phosphate. In a two-year field trial, strain YCP16-23 exhibited remarkable disease suppressing effect by controlling Phytophthora blight (76.24% and 38.09% in years 2017 and 2018, respectively) compared with the untreated control. Strain YCP16-23 caused disease suppression comparable to the microbial fungicides ‘Cike’ (72.04% and 15.41%) and Fluazinam (80.47% and 5.24%). Overall, the results suggest that strain YCP16-23 could provide protection against Phytophthora blight via direct and indirect modes of action and can be used as a biocontrol agent.

Oxathiapiprolin, a Novel Chemical Inducer Activates the Plant Disease Resistance

Oxathiapiprolin was developed as a specific plant pathogenic oomycete inhibitor, previously shown to have highly curative and protective activities against the pepper Phytophthora blight disease under field and greenhouse tests. Therefore, it was hypothesized that oxathiapiprolin might potentially activate the plant disease resistance against pathogen infections. This study investigated the potential and related mechanism of oxathiapiprolin to activate the plant disease resistance using the bacterium Pseudomonas syringae pv tomato (Pst) and plant Arabidopsis interaction as the targeted system. Our results showed that oxathiapiprolin could activate the plant disease resistance against Pst DC3000, a non-target pathogen of oxathiapiprolin, in Arabidopsis, tobacco, and tomato plants. Our results also showed the enhanced callose deposition and H2O2 accumulation in the oxathiapiprolin-treated Arabidopsis under the induction of flg22 as the pathogen-associated molecular pattern (PAMP) treatment. Furthermore, increased levels of free salicylic acid (SA) and jasmonic acid (JA) were detected in the oxathiapiprolin-treated Arabidopsis plants compared to the mock-treated ones under the challenge of Pst DC3000. Besides, the gene expression results confirmed that at 24 h after the infiltration with Pst DC3000, the oxathiapiprolin-treated Arabidopsis plants had upregulated expression levels of the respiratory burst oxidase homolog D (RBOHD), JA-responsive gene (PDF1.2), and SA-responsive genes (PR1, PR2, and PR5) compared to the control. Taken together, oxathiapiprolin is identified as a novel chemical inducer which activates the plant disease resistance against Pst DC3000 by enhancing the callose deposition, H2O2 accumulation, and hormone SA and JA production.