Pseudomonas syringae pv. syringae (Pss) is an emerging phytopathogen that causes Pseudomonas leaf spot (PLS) disease in pepper plants. Pss can cause serious economic damage to pepper production, yet very little is known about the virulence factors carried by Pss that cause disease in pepper seedlings. In this study, Pss strains isolated from pepper plants showing PLS symptoms in Ohio between 2013 and 2021 (n = 16) showed varying degrees of virulence (Pss populations and disease symptoms on leaves) on 6-week-old pepper seedlings. In vitro studies assessing growth in nutrient-limited conditions, biofilm production, and motility also showed varying degrees of virulence, but in vitro and in planta variation in virulence between Pss strains did not correlate. Comparative whole-genome sequencing studies identified notable virulence genes including 30 biofilm genes, 87 motility genes, and 106 secretion system genes. Additionally, a total of 27 antimicrobial resistance genes were found. A multivariate correlation analysis and Scoary analysis based on variation in gene content (n = 812 variable genes) and single nucleotide polymorphisms within virulence genes identified no significant correlations with disease severity, likely due to our limited sample size. In summary, our study explored the virulence and antimicrobial gene content of Pss in pepper seedlings as a first step toward understanding the virulence and pathogenicity of Pss in pepper seedlings. Further studies with additional pepper Pss strains will facilitate defining genes in Pss that correlate with its virulence in pepper seedlings, which can facilitate the development of effective measures to control Pss in pepper and other related P. syringae pathovars.
OBJECTIVE: Pseudomonas leaf spot (PLS) caused by Pseudomonas syringae pv. syringae (Pss) causes significant losses to the pepper industry. Highly virulent Pss strains under optimal environmental conditions (cool-moderate temperatures, high moisture) can cause severe necrotic lesions on pepper leaves that consequently can decrease pepper yield if the disease persists. Hence, it is important to understand the virulence mechanisms of Pss to be able to effectively control PLS in peppers. In our study, in vitro, in planta, and whole-genome sequence analyses were conducted to better understand the virulence and pathogenicity characteristics of Pss strains in peppers. Our findings fill a knowledge gap regarding potential virulence and pathogenicity characteristics of Pss in peppers, including virulence and antimicrobial gene content. Our study helps pave a path to further identify the role of specific virulence genes in causing disease in peppers, which can have implications in developing strategies to effectively control PLS in peppers.

The present study was focused on the pathosystem pepper plants (Capsicum annuum L.)-phytopathogenic bacterium X. euvesicatoria (wild strain 269p)-bacteriophage BsXeu269p/3 and the possibility of bacteriophage-mediated biocontrol of the disease. Two new model systems were designed for the monitoring of the effect of the phage treatment on the infectious process in vivo. The spread of the bacteriophage and the pathogen was monitored by qPCR. A new pair of primers for phage detection via qPCR was designed, as well as probes for TaqMan qPCR. The epiphytic bacterial population and the potential bacteriolytic effect of BsXeu269p/3 in vivo was observed by SEM. An aerosol-mediated transmission model system demonstrated that treatment with BsXeu269p/3 reduced the amount of X. euvesicatoria on the leaf surface five-fold. The needle-pricking model system showed a significant reduction of the amount of the pathogen in infectious lesions treated with BsXeu269p/3 (av. 59.7%), compared to the untreated control. We found that the phage titer is 10-fold higher in the infection lesions but it was still discoverable even in the absence of the specific host in the leaves. This is the first report of in vivo assessment of the biocontrol potential of locally isolated phages against BS pathogen X. euvesicatoria in Bulgaria.

Selenium (Se) maintains soil-plant homeostasis in the rhizosphere and regulates signaling molecules to mitigate cadmium (Cd) toxicity. However, there has been no systematic investigation of the effects of nano-selenium (nano-Se) on the regulation of non-target metabolites and nutritional components in pepper plants under Cd stress. This study investigated the effects of Cd-contaminated soil stress and nano-Se (1, 5, and 20 mg/L) on the metabolic mechanism, fruit nutritional quality, and volatile organic compounds (VOCs) composition of pepper plants. The screening of differential metabolites in roots and fruit showed that most were involved in amino acid metabolism and capsaicin production. Amino acids in roots (Pro, Trp, Arg, and Gln) and fruits (Phe, Glu, Pro, Arg, Trp, and Gln) were dramatically elevated by nano-Se biofortification. The expression of genes of the phenylpropane-branched fatty acid pathway (BCAT, Fat, AT3, HCT, and Kas) was induced by nano-Se (5 mg/L), increasing the levels of capsaicin (29.6%), nordihydrocapsaicin (44.2%), and dihydrocapsaicin (45.3%). VOCs (amyl alcohol, linalool oxide, E-2-heptaldehyde, 2-hexenal, ethyl crotonate, and 2-butanone) related to crop resistance and quality were markedly increased in correspondence with the nano-Se concentration. Therefore, nano-Se can improve the health of pepper plants by regulating the capsaicin metabolic pathway and modulating both amino acid and VOC contents.

Most studies have focused on regulation in a metabolic pathway in response to exogenous selenium under cadmium stress, rather than the change of key factors in soil and pepper plants. In this study, the correlations in environmental variables, microorganisms, metabolic pathways, Se and Cd morphology under nano-Se intervention were examined using metabolomics and microbial diversity in rhizosphere soil and pepper plants. The principal forms of Se in the soils were Se (VI) and SeCys, while SeMet and MeSeCys were the main components in the root, stem, leaves, and fruits in the treatment of nano-Se (5 and 20 mg/L) relative to the control. Soil enzymes,metabolites (fluorescein diacetate, urease, brassinolide, and p-hydroxybenzonic acid), and plant metabolites (rutin, luteolin, brassinolide, and abscisic acid) were remarkably enhanced by nano-Se fortification. The bio-enhancement of nano-Se can boost the beneficial microorganisms of Gammaproteobacteria, Alphaproteobacteria, Bacteroidia, Gemmatimonadetes, Deltaproteobacteria, and Anaerolineae in rhizosphere soil. Changes in microbial community were found to be strongly linked to the environment index, enzymes, soil metabolites, Se forms, which reduced Cd bioavailability and Cd accumulation in pepper plants. In conclusion, the nano-Se application integrates soil-plant balance by improving soil qualities and assigning signaling molecule levels in rhizosphere soil and pepper plants.

Selenium (Se) can promote the growth and resistance of agricultural crops as fertilizers, while the role of nano-selenium (nano-Se) against Cd remains unclear in pepper plants (Capsicum annuum L.). Biofortification with nano-Se observably restored Cd stress by decreasing the level of Cd in plant tissues and boosting the accumulation in biomass. The Se compounds transformed by nano-Se were primarily in the form of SeMet and MeSeCys in pepper tissues. Differential metabolites and the genes of plant signal transduction and lignin biosynthesis were measured by employing transcriptomics and determining target metabolites. The number of lignin-related genes (PAL, CAD, 4CL, and COMT) and contents of metabolites (sinapyl alcohol, phenylalanine, p-coumaryl alcohol, caffeyl alcohol, and coniferaldehyde) were remarkably enhanced by treatment with Cd1Se0.2, thus, maintaining the integrity of cell walls in the roots. It also enhanced signal transduction by plant hormones and responsive resistance by inducing the biosynthesis of genes (BZR1, LOX3, and NCDE1) and metabolites (brassinolide, abscisic acid, and jasmonic acid) in the roots and leaves. In general, this study can enable a better understanding of the protective mechanism of nano-Se in improving the capacity of plants to resist environmental stress.

In 2004, bacterial spot-causing xanthomonads (BSX) were reclassified into 4 species-Xanthomonas euvesicatoria, X. vesicatoria, X. perforans, and X. gardneri. Bacterial spot disease on pepper plant in Korea is known to be caused by both X. axonopodis pv. vesicatoria and X. vesicatoria. Here, we reidentified the pathogen causing bacterial spots on pepper plant based on the new classification. Accordingly, 72 pathogenic isolates were obtained from the lesions on pepper plants at 42 different locations. All isolates were negative for pectolytic activity. Five isolates were positive for amylolytic activity. All of the Korean pepper isolates had a 32 kDa-protein unique to X. euvesicatoria and had the same band pattern of the rpoB gene as that of X. euvesicatoria and X. perforans as indicated by PCR-restriction fragment length polymorphism analysis. A phylogenetic tree of 16S rDNA sequences showed that all of the Korean pepper plant isolates fit into the same group as did all the reference strains of X. euvesicatoria and X. perforans. A phylogenetic tree of the nucleotide sequences of 3 housekeeping genes-gapA, gyrB, and lepA showed that all of the Korean pepper plant isolates fit into the same group as did all of the references strains of X. euvesicatoria. Based on the phenotypic and genotypic characteristics, we identified the pathogen as X. euvesicatoria. Neither X. vesicatoria, the known pathogen of pepper bacterial spot, nor X. perforans, the known pathogen of tomato plant, was isolated. Thus, we suggest that the pathogen causing bacterial spot disease of pepper plants in Korea is X. euvesicatoria.

Endophytic bacteria may act individually or in consortia in controlling certain plant diseases. In this study, pepper plants (Capsicum annuum L. cv. Nokkwang) were cultivated in glasshouse conditions using field soils collected from two different geographic locations, Deokso (DS) and Gwangyang (GY) in Korea. Community structure and antifungal activity of pepper endophytic bacteria were analyzed using culture-independent (PCR-DGGE) and culture-dependent (plating) methods, respectively. Dissimilarities were observed between DGGE profiles of DS and GY samples at all plant tissues. However, sequencing of the major DGGE bands revealed an enrichment of Firmicutes in the leaves of plants propagated in either soil. Similar results were observed with the culturable assays. Firmicutes dominated the isolates from both leaf samples, DS leaf (100 %) and GY leaf (83.3 %), although the genus compositions of DS leaf and GY leaf isolates were different. We assessed the antifungal activity of each isolate recovered to better understand the potential role that these endophytic bacteria may play. Of the 27 representative isolates from DS plant samples, 17 isolates (63.0 %) had antagonistic activity against at least one of the fungi tested. Seventeen isolates from GY plant samples (58.6 %) displayed antagonistic properties. The results show that the endophytic communities differ in the same plant species when propagated in different soils. Exploring the internal tissues of plants growing in diverse soil environments could be a way to find potential candidates for biocontrol agents.

Integrated Pest Management strategies are widely implemented in sweet peppers. Aphid biological control on sweet pepers includes curative applications of parasitoids and generalist predators, but with limited efficiency. Macrolophus pygmaeus is a zoophytophagous predator which has been reported to predate on aphids, but has traditionally been used to control other pests, including whiteflies. In this work, we evaluate the effectiveness of M. pygmaeus in controlling Myzus persicae (Homoptera: Aphididae) by testing different combinations of aphid and predator densities in cage-experiments under greenhouse conditions. The impact of the presence of an alternative factitious prey (E. kuehniella eggs) was also investigated. Macrolophus pygmaeus, at densities of four individuals/plant, caused rapid decline of newly established aphid populations. When aphid infestations were heavy, the mirid bug reduced the aphid numbers but did not fully eradicate aphid populations. The availability of a factitious prey did not influence M. pygmaeus predation on aphids. Based on our data, preventive application of M. pygmaeus, along with a supplementary food source , is recommended to control early infestations of aphids.