Potential of microbial endophytes to enhance the resistance to postharvest diseases of fruit and vegetables

Endophyte mediated biocontrol mechanisms of phytopathogens in agriculture

The global human population is growing and demand for food is increasing. Global agriculture faces numerous challenges, including excessive application of synthetic pesticides, emergence of herbicide-and pesticide-resistant pathogenic microbes, and more frequent natural disasters associated with global warming. Searches for valuable endophytes have increased, with the aim of making agriculture more sustainable and environmentally friendly. Endophytic microbes are known to have a variety of beneficial effects on plants. They can effectively transfer nutrients from the soil into plants, promote plant growth and development, increase disease resistance, increase stress tolerance, prevent herbivore feeding, reduce the virulence of pathogens, and inhibit the growth of rival plant species. Endophytic microbes can considerably minimize the need for agrochemicals, such as fertilizers, fungicides, bactericides, insecticides, and herbicides in the cultivation of crop plants. This review summarizes current knowledge on the roles of endophytes focusing on their mechanisms of disease control against phytopathogens through the secretion of antimicrobial substances and volatile organic compounds, and the induction of systemic resistance in plants. Additionally, the beneficial roles of these endophytes and their metabolites in the control of postharvest diseases in plants have been summarized.

Volatile Organic Compounds of Wickerhamomyces anomalus Prevent Postharvest Black Spot Disease in Tomato

Postharvest diseases, such as black spots caused by Alternaria alternata, have caused huge economic losses to the tomato industry and seriously restricted its development. In recent years, biological control has become a new method to control postharvest diseases of fruits and vegetables. Our research group screened W. anomalus, a yeast demonstrating a promising control effect on a postharvest black spot disease of tomatoes, and explored its physiological mechanism of prevention and control. Therefore, this study investigated the prevention and control effect of metabolites of W. anomalus on tomato black spot disease and the inhibition effect of main components on A. alternata. A GC-MS analysis found that isoamyl acetate was the main component of W. anomalus that played an inhibitory role. The results showed that isoamyl acetate could inhibit the growth of A. alternata and had a certain control effect on postharvest black spots in tomatoes. Our findings suggest that isoamyl acetate could be a promising alternative to fungicides for controlling postharvest black spots in tomatoes.

Endophytic Fungi Volatile Organic Compounds as Crucial Biocontrol Agents Used for Controlling Fruit and Vegetable Postharvest Diseases

Fruits and vegetables are an important part of the human diet, but during transportation and storage, microbial pathogens attack and spoil fruits and vegetables, causing huge economic losses to agriculture. Traditionally used chemical fungicides leave chemical residues, leading to environmental pollution and health risks. With the emphasis on food safety, biocontrol agents are attracting more and more attention due to their environmental friendliness. Endophytic fungi are present in plant tissues and do not cause host disease. The volatile organic compounds (VOCs) they produce are used to control postharvest diseases due to their significant antifungal activity, as well as their volatility, safety and environmental protection characteristics. This review provides the concept and characterization of endophytic fungal VOCs, concludes the types of endophytic fungi that release antifungal VOCs and their biological control mechanisms, as well as focuses on the practical applications and the challenges of applying VOCs as fumigants. Endophytic fungal VOCs can be used as emerging biocontrol resources to control postharvest diseases that affect fruits and vegetables.

Comparative physiological and transcriptomic analysis reveals an improved biological control efficacy of Sporidiobolus pararoseus Y16 enhanced with ascorbic acid against the oxidative stress tolerance caused by Penicillium expansum in pears

Sporidiobolus pararoseus Y16, a species of significant ecological importance, has distinctive physiological and biological regulatory systems that aid in its survival and environmental adaptation. The goal of this investigation was to understand the complex interactions between physiological and molecular mechanisms in pear fruits as induced by S. pararoseus Y16. The study investigated the use of S. pararoseus Y16 and ascorbic acid (VC) in combination in controlling blue mold decay in pears via physiological and transcriptomic approach. The study results showed that treatment of S. pararoseus Y16 with 150 μg/mL VC reduced pears blue mold disease incidence from 43% to 11%. Furthermore, the combination of S. pararoseus Y16 and VC significantly inhibited mycelia growth and spore germination of Penicillium expansum in the pear's wounds. The pre-treatment did not impair post-harvest qualities of pear fruit but increased antioxidant enzyme activity specifically polyphenol oxidase (PPO), peroxidase (POD), catalase (CAT) activities as well as phenylalanine ammonia-lyase (PAL) enzyme activity. The transcriptome analysis further uncovered 395 differentially expressed genes (DEGs) and pathways involved in defense mechanisms and disease resistance. Notable pathways of the DEGs include plant-pathogen interaction, tyrosine metabolism, and hormone signal transduction pathways. The integrative approach with both physiological and transcriptomic tools to investigate postharvest pathology in pear fruits with clarification on how S. pararoseus Y16 enhanced with VC, improved gene expression for disease defense, and create alternative controls strategies for managing postharvest diseases.

A polyphasic molecular approach to characterize a collection of grapevine endophytic bacteria with bioprotective potential

AIMS

The work presented here was conducted to characterize the biodiversity of a collection of bacterial isolates, mainly wood endophytes, as part of a research project focused on exploring their bioprotective potential for postharvest biological control of fruits.

METHODS AND RESULTS

This work was the basis for the development of a tailored method combining 16S rDNA sequencing and Rep-PCR to differentiate the isolates and identify them to genus level or below. More than one hundred isolates obtained from wood and roots of different grapevine genotypes were cultured on appropriate growth media and then subjected to the specified multistep molecular identification.

CONCLUSIONS

We have obtained good dereplication for grapevine-endophytic bacteria, together with reliable genetic identification. Both are essential prerequisites to properly characterize a biome bank and, at the same time, beneficial prerequisites to subsequently perform a correct bioprotection assessment.

Endophytic Bacillus subtilis H17-16 effectively inhibits Phytophthora infestans, the pathogen of potato late blight, and its potential application

BACKGROUND

As a highly prevalent epidemic disease of potato, late blight caused by Phytophthora infestans poses a serious threat to potato yield and quality. At present, chemical fungicides are mainly used to control potato late blight, but long-term overuse of chemical fungicides may lead to environmental pollution and human health threats. Endophytes, natural resources for plant diseases control, can promote plant growth, enhance plant resistance, and secrete antifungal substances. Therefore, there is an urgent need to find some beneficial endophytes to control potato late blight.

RESULTS

We isolated a strain of Bacillus subtilis H17-16 from potato healthy roots. It can significantly inhibit mycelial growth, sporangia germination and the pathogenicity of Phytophthora infestans, induce the resistance of potato to late blight, and promote potato growth. In addition, H17-16 has the ability to produce protease, volatile compounds (VOCs) and form biofilms. After H17-16 treatment, most of the genes involved in metabolism, virulence and drug resistance of Phytophthora infestans were down-regulated significantly, and the genes related to ribosome biogenesis were mainly up-regulated. Moreover, field and postharvest application of H17-16 can effectively reduce the occurrence of potato late blight, and the combination of H17-16 with chitosan or chemical fungicides had a better effect than single H17-16.

CONCLUSION

Our results reveal that Bacillus subtilis H17-16 has great potential as a natural fungicide for controlling potato late blight, laying a theoretical basis for its development as a biological control agent. © 2023 Society of Chemical Industry.

Prolong the postharvest shelf life of spinach through the antioxidative ability of melatonin

Spinach is also known as Persian cuisine, it is rich in nutrients such as protein, vitamin C and minerals, and has high nutritional value. In this study, Spinach was treated with melatonin in order to prolong its shelf life. Melatonin has strong antioxidant effects as an endogenous free radical scavenger. The spinach was sprayed with 0.10, 0.20 and 0.30 mg/mL melatonin solution after harvesting, and distilled water was used as control for low temperature storage at 4 °C. The results showed that melatonin spraying Spinach delayed the degradation of chlorophyll, especially the treatment of 0.20 mg/mL melatonin was the most effective. The content of soluble sugar and soluble protein in spinach tissue was kept high, the accumulation of malondialdehyde (MDA) was reduced, and the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) were increased. These findings suggested that melatonin treatment may be a useful technique to prolong the postharvest life of spinach and improve its quality.

Post-harvest biocontrol of Fusarium infection in tomato fruits using bio-mediated selenium nanoparticles

The protection of post-harvest infection by Fusarium spp. is a major worldwide demand, especially using effective natural alternatives to chemical fungicides. In this respect, selenium nanoparticles (SeNPs) were biosynthesized using Fenugreek seeds aqueous extract. Bio-mediated SeNPs were characterized using XRD, FTIR, UV-Vis, TEM, and EDX. XRD confirmed the crystalline nature with six characteristic peaks corresponding to Se-nanocrystals. TEM showed spherical-shaped SeNPs with 34.02-63.61 nm diameter. FTIR verified the presence of different bio-functional groups, such as, N-H, O-H, C-N, and C-NH2 acting as stabilizing/reducing agents during the biosynthesis. Bio-mediated SeNPs exhibited excellent biocidal activity against F. oxysporum and F. moniliforme, with MIC of 0.25 and 1.7 mg/mL, respectively. Direct treatment of F. oxysporum with SeNPs led to significant deformation and lysis of the fungal hyphae within 18 h. The treatment of infected fruits with MIC of SeNPs reduced the infection signs by 100% and preserved the fresh-like appearance of treated fruits for 25 and 35 days when stored at 25 °C and 5 °C, respectively. Therefore, SeNPs is considered efficacious fungicidal against Fusarium spp. in-vitro and in-vivo. The treatment of tomato fruits with MIC of SeNPs positively affected its chemical properties, as well as decreased weight loss %, confirming the barrier effect of SeNPs, thus increasing fruits' shelf-life. Bio-mediated SeNPs appeared safe towards normal HSF and OEC cell lines with IC50> 300 μg/mL. Overall results recommend the usage of bio-mediated SeNPs as safe powerful bioagent against Fusarium infection, maintaining tomato quality, and providing protection from post-harvest invasion and/or destroying existing infections.

Insights into the Isolation, Identification, and Biological Characterization Analysis of and Novel Control Strategies for Diaporthe passiflorae in Postharvest Passion Fruit

Postharvest diseases seriously restrict developments in the passion fruit industry. In this study, we aimed to identify the postharvest pathogen affecting passion fruit, investigate its pathogenicity, and explore relevant control methods. The pathogen was isolated from rotting passion fruit and identified using morphological characteristics, ITS sequences, and phylogenetic tree analyses. Additionally, preliminary studies were conducted to assess the biological characteristics of the pathogen and evaluate the efficacy of various treatments for disease control. The fungus on the passion fruit called B4 was identified as Diaporthe passiflorae. Optimal conditions for mycelial growth were observed at 25-30 °C and pH 5-6, with starch as the carbon source and peptone as the nitrogen source. Infection by D. passiflorae accelerated fruit decay, reduced the h° value of the peel, and increased the peel cell membrane permeability when compared to the control. Notably, treatments with appropriate concentrations of ɛ-poly-l-lysine, salicylic acid, and melatonin showed inhibitory effects on the pathogen's growth in vitro and may thus be potential postharvest treatments for controlling brown rot caused by D. passiflorae in passion fruit. The results provide a scientific basis for the development of strategies to control postharvest decay and extend the storage period of passion fruit.

Anticancer and Antiphytopathogenic Activity of Fluorinated Isatins and Their Water-Soluble Hydrazone Derivatives

A series of new fluorinated 1-benzylisatins was synthesized in high yields via a simple one-pot procedure in order to explore the possible effect of ortho-fluoro (3a), chloro (3b), or bis-fluoro (3d) substitution on the biological activity of this pharmacophore. Furthermore, the new isatins could be converted into water-soluble isatin-3-hydrazones using their acid-catalyzed reaction with Girard's reagent P and its dimethyl analog. The cytotoxic action of these substances is associated with the induction of apoptosis caused by mitochondrial membrane dissipation and stimulated reactive oxygen species production in tumor cells. In addition, compounds 3a and 3b exhibit platelet antiaggregation activity at the level of acetylsalicylic acid, and the whole series of fluorine-containing isatins does not adversely affect the hemostasis system as a whole. Among the new water-soluble pyridinium isatin-3-acylhydrazones, compounds 7c and 5c,e exhibit the highest antagonistic effect against phytopathogens of bacterial and fungal origin and can be considered useful leads for combating plant diseases.

Anti-oomycete ability of scopolamine against Phytophthora infestans, a terrible pathogen of potato late blight

BACKGROUND

Phytophthora infestans causes late blight, threatening potato production. The tropane alkaloid scopolamine from some industrial plants (Datura, Atropa, etc.) has a broad-spectrum bacteriostatic effect, but its effect on P. infestans is unknown.

RESULTS

In the present study, scopolamine inhibited the mycelial growth of phytopathogenic oomycete P. infestans, and the half-maximal inhibitory concentration (IC50 ) was 4.25 g L-1 . The sporangia germination rates were 61.43%, 16.16%, and 3.99% at concentrations of zero (control), 0.5 IC50 , and IC50 , respectively. The sporangia viability of P. infestans was significantly reduced after scopolamine treatment through propidium iodide and fluorescein diacetate staining, speculating that scopolamine destroyed cell membrane integrity. The detached potato tuber experiment demonstrated that scopolamine lessened the pathogenicity of P. infestans in potato tubers. Under stress conditions, scopolamine showed good inhibition of P. infestans, indicating that scopolamine could be used in multiple adverse conditions. The combination effect of scopolamine and the chemical pesticide Infinito on P. infestans was more effective than the use of scopolamine or Infinito alone. Moreover, transcriptome analysis suggested that scopolamine leaded to a downregulation of most P. infestans genes, functioning in cell growth, cell metabolism, and pathogenicity.

CONCLUSION

To our knowledge, this is the first study to detect scopolamine inhibitory activity against P. infestans. Also, our findings highlight the potential of scopolamine as an eco-friendly option for controlling late blight in the future. © 2023 Society of Chemical Industry.

Research progress of volatile organic compounds produced by plant endophytic bacteria in control of postharvest diseases of fruits and vegetables

Pathogen infestation results in significant losses of fruits and vegetables during handling, transportation, and storage. The use of synthetic fungicides has been a common measure for controlling plant pathogens. However, their excessive use of chemicals has led to increased environmental pollution, leaving large amounts of chemicals in agricultural products, posing a threat to human and animal health. There is now an increasing amount of research activities to explore safer and more innovative ways to control plant pathogens. In this regard, endophytic bacteria contribute significantly. Endophytic bacteria are ubiquitous in the internal tissues of plants without causing damage or disease to the host. Due to their high volatility and difficulties in residue in fruits and vegetables, volatile organic chemicals (VOCs) produced by endophytic bacteria have received a lot of attention in recent years. VOCs are a potential biofumigant for the effective control of postharvest fruits and vegetables diseases. This review focuses mainly on the recent progress in using endophytic bacteria VOCs to control post-harvest fruits and vegetables disease. This review provides a brief overview of the concept, characteristics, and summarises the types, application effect, and control mechanisms of endophytic bacterial VOCs. The research area that is being developed has great application value in agriculture and living practice.

Isolation and Screening of Antagonistic Endophytes against Phytophthora infestans and Preliminary Exploration on Anti-oomycete Mechanism of Bacillus velezensis 6-5

Phytophthora infestans, the notorious pathogen of potato late blight, leads to a severe decline in potato yields and even harvest failure. We isolated 201 endophytic isolates from healthy root tissues of potatoes, among which 41 showed strong antagonistic activity against P. infestans. Further, the tolerance to stress and the potential application against potato late blight of these antagonistic isolates were tested. Most of them were extremely tolerant to stresses such as acid-alkali, temperature, UV, salt, and heavy metal stress. However, some antagonistic isolates with excellent stress tolerance might be pathogenic to potatoes. Combining the screening results, a total of 14 endophytes had excellent comprehensive performance in all the tests. In this paper, the endophyte 6-5 was selected among them for the preliminary exploration of the anti-oomycete mechanism. Analysis of the 16S rDNA sequence revealed that 6-5 had a high homology to the corresponding sequence of Bacillus velezensis (99.72%) from the NCBI database. Endophyte 6-5 significantly inhibited the mycelial growth of P. infestans, with an inhibition rate of over 90% in vitro assays, and deformed the hyphal phenotype of P. infestans. In addition, endophyte 6-5 could secrete protease and cellulase, and produce antagonistic substances with high thermal stability, which might be helpful to its antagonistic activity against P. infestans. Furthermore, it was demonstrated that 6-5 had the ability to improve the resistance of potato tubers to late blight. In short, our study described the process of isolating and screening endophytes with antagonistic activity against P. infestans from potato roots, and further explored the potential of biocontrol candidate strain 6-5 in potato late blight control.

Deciphering the role of endophytic microbiome in postharvest diseases management of fruits: Opportunity areas in commercial up-scale production

As endophytes are widely distributed in the plant's internal compartments and despite having enormous potential as a biocontrol agent against postharvest diseases of fruits, the fruit-endophyte-pathogen interactions have not been studied detail. Therefore, this review aims to briefly discuss the colonization patterns of endophytes and pathogens in the host tissue, the diversity and distribution patterns of endophytes in the carposphere of fruits, and host-endophyte-pathogen interactions and the molecular mechanism of the endophytic microbiome in postharvest disease management in fruits. Postharvest loss management is one of the major concerns of the current century. It is considered a critical challenge to food security for the rising global population. However, to manage the postharvest loss, still, a large population relies on chemical fungicides, which affect food quality and are hazardous to health and the surrounding environment. However, the scientific community has searched for alternatives for the last two decades. In this context, endophytic microorganisms have emerged as an economical, sustainable, and viable option to manage postharvest pathogens with integral colonization properties and eliciting a defense response against pathogens. This review extensively summarizes recent developments in endophytic interactions with harvested fruits and pathogens-the multiple biocontrol traits of endophytes and colonization and diversity patterns of endophytes. In addition, the upscale commercial production of endophytes for postharvest disease treatment is discussed.

Bitter friends are not always toxic: The loss of acetic acid bacteria and the absence of Komagataeibacter in the gut microbiota of the polyphagous fly Anastrepha ludens could inhibit its development in Psidium guajava in contrast to A. striata and A. fraterculus that flourish in this host

The gut microbiota is key for the homeostasis of many phytophagous insects, but there are few studies comparing its role on host use by stenophagous or polyphagous frugivores. Guava (Psidium guajava) is a fruit infested in nature by the tephritids Anastrepha striata and A. fraterculus. In contrast, the extremely polyphagous A. ludens infests guava only under artificial conditions, but unlike A. striata and the Mexican A. fraterculus, it infests bitter oranges (Citrus x aurantium). We used these models to analyze whether the gut microbiota could explain the differences in host use observed in these flies. We compared the gut microbiota of the larvae of the three species when they developed in guava and the microbiota of the fruit pulp larvae fed on. We also compared the gut microbiota of A. ludens developing in C. x aurantium with the pulp microbiota of this widely used host. The three flies modified the composition of the host pulp microbiota (i.e., pulp the larvae fed on). We observed a depletion of Acetic Acid Bacteria (AAB) associated with a deleterious phenotype in A. ludens when infesting P. guajava. In contrast, the ability of A. striata and A. fraterculus to infest this fruit is likely associated to a symbiotic interaction with species of the Komagataeibacter genus, which are known to degrade a wide spectrum of tannins and polyphenols. The three flies establish genera specific symbiotic associations with AABs. In the case of A. ludens, the association is with Gluconobacter and Acetobacter, but importantly, it cannot be colonized by Komagataeibacter, a factor likely inhibiting its development in guava.

Distribution pattern of endophytic bacteria and fungi in tea plants

Endophytes are critical for plant growth and health. Tea is an economically important crop in China. However, little is known about the distribution pattern and potential functions of endophytic communities in tea trees. In this study, two genotypes (BXZ and MF) cultivated under the same conditions were selected, and endophytic bacteria and fungi were analyzed through 16S rRNA and ITS high-throughput sequencing technologies, respectively. For endophytic bacteria, root tissues harbored the most diverse endophytes, followed by stems and old leaves, and new leaves possessed the lowest diversity. In contrast, old leave tissues harbored more diverse endophytic fungi than did root and stem tissues. Most of the dominant endophytes showed obvious cultivar and tissue preferences. Tissue type played a more important role in shaping community structure than did cultivar. Nevertheless, some endophytic bacterial groups, which mainly affiliated to Chryseobacterium, Sphingomonas, Rhizobium, Morganella, Methylobacterium and Comamonadaceae, could parasitize different tissues, and the average relative abundance of endophytic bacteria was as high as 72.57%. Some endophytic fungal populations, such as Colletotrichum, Uwebraunia, Cladosporium, and Devriesia, could also parasitize tea, and the relative abundance accounted for approximately 25.70–97.26%. The cooperative relationship between endophytic bacteria and fungi in the new leaves was stronger than that in the old leaves, which can better participate in the metabolism of tea material.

Endophytes from blueberry (Vaccinium sp.) fruit: Characterization of yeast and bacteria via label-free surface-enhanced Raman spectroscopy (SERS)

Blueberries (Vaccinium sp.) are consumed all around the globe, however, their endophytic community has not been thoroughly researched, specifically their fruit endophytes. We aimed to isolate and analyze easily cultivable blueberry fruit endophytes to help in future research, concerning probiotic microorganisms. Twelve strains were isolated in this pilot study, genetically homologous with Staphylococcus hominis, Staphylococcus cohnii, Salmonella enterica, Leuconostoc mesenteroides, and [Candida] santamariae. To determine the molecular composition of these isolates we used label-free surface-enhanced Raman spectroscopy (SERS). To our knowledge, this is the first time that SERS spectra for L. mesenteroides and C. santamariae are presented, as well as the first report of Candida yeast, isolated specifically from blueberry fruits. Our findings suggest that the differences in tested yeast and bacteria SERS spectra and subsequent differentiation are facilitated by minor shifts in spectral peak positions as well as their intensities. Moreover, we used principal component and discriminant function analyses to differentiate chemotypes within our isolate group, proving the sensitivity of the technique and its usefulness to recognize different strains in plant-associated microbe samples, which will aid to streamline future studies in biofertilizers and biocontrol agents.

Comprehensive Review of Fungi on Coffee

Coffee is grown in more than 80 countries as a cash crop and consumed worldwide as a beverage and food additive. It is susceptible to fungal infection during growth, processing and storage. Fungal infections, in particular, can seriously affect the quality of coffee and threaten human health. The data for this comprehensive review were collected from the United States Department of Agriculture, Agricultural Research Service (USDA ARS) website and published papers. This review lists the fungal species reported on coffee based on taxonomy, life mode, host, affected plant part and region. Five major fungal diseases and mycotoxin-producing species (post-harvest diseases of coffee) are also discussed. Furthermore, we address why coffee yield and quality are affected by fungi and propose methods to control fungal infections to increase coffee yield and improve quality. Endophytic fungi and their potential as biological control agents of coffee disease are also discussed.

Bacterial Endophyte Community Dynamics in Apple (Malus domestica Borkh.) Germplasm and Their Evaluation for Scab Management Strategies

The large genetic evolution due to the sexual reproduction-mediated gene assortments and propensities has made Venturia inaequalis (causing apple scab) unique with respect to its management strategies. The resistance in apple germplasm against the scab, being controlled for by more than fifteen genes, has limited gene alteration-based investigations. Therefore, a biological approach of bacterial endophyte community dynamics was envisioned across the apple germplasm in context to the fungistatic behavior against V. inaequalis. A total of 155 colonies of bacterial endophytes were isolated from various plant parts of the apple, comprising 19 varieties, and after screening for antifungal behavior followed by morphological, ARDRA, and sequence analysis, a total of 71 isolates were selected for this study. The alpha diversity indices were seen to fluctuate greatly among the isolation samples in context to microflora with antifungal behavior. As all the isolates were screened for the presence of various metabolites and some relevant genes that directly or indirectly influence the fungistatic behavior of the isolated microflora, a huge variation among the isolated microflora was observed. The outstanding isolates showing highest percentage growth inhibition of V. inaequalis were exploited to raise a bio-formulation, which was tested against the scab prevalence in eight apple varieties under controlled growth conditions. The formulation at all the concentrations caused considerable reductions in both the disease severity and disease incidence in all the tested apple varieties. Red Delicious being most important cultivar of the northwestern Himalayas was further investigated for its biochemical behavior in formulation and the investigation revealed different levels of enzyme production, chlorophyll, and sugars against the non-inoculated control.

Insights into the relevance between bacterial endophytic communities and resistance of rice cultivars infected by Xanthomonas oryzae pv. oryzicola

Bacterial leaf streak (BLS) caused by Xanthomonas oryzae pv. oryzicola (Xoc), impacts the production of rice. However, several rice cultivars displayed resistance to Xoc in the field, but scarce information is available about the role of endophytic microbiota in disease resistance. In the present study, the endophytic bacterial communities of resistant and susceptible rice cultivars "CG2" and "IR24", respectively, were analyzed using high throughput 16S rRNA gene amplified sequencing and culture dependent method was further used for bacterial isolation. A total of 452,716 high-quality sequences representing 132 distinct OTUs (Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes) and 46 isolates of 16 genera were explored from rice leaves infected with Xoc. Community diversity of endophytic bacteria were higher in the leaves of the resistant cultivars compared to susceptible cultivars upon Xoc infection. Strikingly, this diversity might contribute to natural defense of the resistant cultivar against pathogen. Pantoea, which is pathogen antagonist, was frequently detected in two cultivars and higher abundance were recorded in resistant cultivars. Different abundance genus includes endophytic isolates with marked antagonistic activity to Xoc. The increased proportions of antagonistic bacteria, may contribute to resistance of rice cultivar against Xoc and the Pantoea genus was recruited by Xoc infection play a key role in suppressing the development of BLS disease in rice. Taken together, this work reveals the association between endophytic bacteria and BLS resistance in rice and identification of antagonism-Xoc bacterial communities in rice.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02979-2.

An overview on endophytic bacterial diversity habitat in vegetables and fruits

Nowadays, scientific research revolution is going on in many areas, and the human health is one of them. However, in the earlier studies, it was observed that most of the people health in the world affects by consumptions of contaminated food which is dangerous for human health and country economy. Recent studies showed that the fresh vegetables and fruits are the major habitat for endophytic bacterial communities. Salmonella and Escherichia coli both are the very common bacteria founds in fresh vegetables and fruits. Generally, many people eat vegetables and fruits without cooking (in the form of salad). The continued assumption of such food increases the health risk factor for foodborne diseases. So, from the last decades, many researchers working to understand about the relationship of endophytic microbes with plants either isolated bacteria are pathogenic or nonpathogenic. Moreover, most of the endophytes were identified by using 16S rRNA sequencing method. Hence, this review elaborates on the differences and similarities between nonpathogenic and pathogenic endophytes in terms of host plant response, colonization strategy, and genome content. Furthermore, it is emphasized on the environmental effects and biotic interactions within plant microbiota that influence pathogenesis and the pathogenesis.

Genomic Analysis and Secondary Metabolites Production of the Endophytic Bacillus velezensis Bvel1: A Biocontrol Agent against Botrytis cinerea Causing Bunch Rot in Post-Harvest Table Grapes

Botrytis bunch rot caused by Botrytis cinerea is one of the most economically significant post-harvest diseases of grapes. In the present study, we showed that the bacterial strain Bvel1 is phylogenetically affiliated to Bacillus velezensis species. The strain Bvel1 and its secreted metabolites exerted an antifungal activity, under in vitro conditions, against B. cinerea. UHPLC-HRMS chemical analysis revealed that iturin A2, surfactin-C13 and -C15, oxydifficidin, bacillibactin, L-dihydroanticapsin, and azelaic acid were among the metabolites secreted by Bvel1. Treatment of wounded grape berries with Bacillus sp. Bvel1 cell culture was effective for controlling grey mold ingress and expansion in vivo. The effectiveness of this biological control agent was a function of the cell culture concentration of the antagonist applied, while preventive treatment proved to be more effective compared to curative. The strain Bvel1 exhibited an adequate colonization efficiency in wounded grapes. The whole-genome phylogeny, combined with ANI and dDDH analyses, provided compelling evidence that the strain Bvel1 should be taxonomically classified as Bacillus velezensis. Genome mining approaches showed that the strain Bvel1 harbors 13 antimicrobial biosynthetic gene clusters, including iturin A, fengycin, surfactin, bacilysin, difficidin, bacillaene, and bacillibactin. The results provide new insights into the understanding of the endophytic Bacillus velezensis Bvel1 biocontrol mechanism against post-harvest fungal pathogens, including bunch rot disease in grape berries.

Medicinal Plants and Their Bacterial Microbiota: A Review on Antimicrobial Compounds Production for Plant and Human Health

Medicinal plants (MPs) have been used since antiquity in traditional and popular medicine, and they represent a very important source of bioactive molecules, including antibiotic, antiviral, and antifungal molecules. Such compounds are often of plant origin, but in some cases, an origin or a modification from plant microbiota has been shown. Actually, the research continues to report the production of bioactive molecules by plants, but the role of plant–endophytic interaction is emerging. Classic examples are mainly concerned with fungal endophytes; however, it has been recently shown that bacterial endophytes can also play an important role in influencing the plant metabolism related to the synthesis of bioactive compounds. In spite of this, a deep investigation on the power of MP bacterial endophytes is lacking. Here, an overview of the studies on MP bacterial microbiota and its role in the production of plant antimicrobial compounds contributing to prime host defense system and representing a huge resource for biotech and therapeutic applications is provided.