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The soybean is recognized worldwide as one of the most important crops due to its protein- and oil-rich seeds. Several beneficial bacterial strains, including those of the genus Pseudomonas, are known to increase plant yield and disease tolerance. The aim of this study was to test the potential of 15 strains of Pseudomonas spp. to promote soybean growth under field conditions. Strains were identified based on 16S rRNA and gyrB sequences, and strains belonging to risk group 1 were further analyzed. Selected strains were tested for plant growth-promoting (PGP) properties, biofilm formation and in vitro antimicrobial activity against various fungal pathogens. PGP activity indicators of the selected strains were evaluated on soybean plants grown in fertilizer-free soil and in soil treated with 70% and 100% fertilizers. Three Pseudomonas spp. strains, P. putida VB131A, P. fulva VB134B and P. rhodesiae VB143S, were selected as PGP candidates. All three strains showed the ability to produce IAA and solubilize phosphorus, while only P. rhodesiae VB143S showed strong lipase and protease activity. Only P. fulva VB134B showed the ability to produce biofilm and hydrogen cyanide. All three strains showed in vitro antifungal activity against Alternaria infectoria. P. fulva VB134B and P. rhodesiae VB143S showed antifungal activity against Alternaria alternata and P. putida VB131A and P. rhodesiae VB143S against Epicoccum nigrum. Only P. fulva VB134B showed activity against Monilinia laxa. Statistically significant differences in plant height were not observed regardless of the strain or soil treatment used. In terms of first pod height, the P. fulva VB134B treatment was most effective when applied to soybeans grown in 100% fertilized soil. In contrast, plants treated with P. rhodesiae VB143S and grown in 100% fertilized soil had the highest number of branches and pods per plant.

The pygidial glands of carabids produce strong-smelling vapours. In this study, we examined the chemical composition of the gland secretions and the structure of the glands in five species of Carabini ground beetles (one species from the subtribe Calosomatina and four species from the subtribe Carabina): Calosoma (Calosoma) maderae (Fabricius, 1775), Carabus (Carabus) granulatus Linnaeus, 1758, C. (Limnocarabus) clathratus Linnaeus, 1760, C. (Carabus) ulrichii Germar, 1823, and C. (Procerus) gigas Creutzer, 1799. Additionally, we tested the antibacterial potential of the pygidial gland secretions of the two latter species against 11 bacterial strains. In order to detect the chemical content of the secretions, we used gas chromatography–mass spectrometry (GC–MS). The secretion extracts were applied against selected strains of medically important bacteria. We used bright-field microscopy to examine the morphology of the glands. We discovered a total of 11 chemical compounds in the pygidial gland extracts of the ground beetles we analysed. Ten of these compounds were identified as seven carboxylic acids, two hydrocarbons, and one aromatic aldehyde, while one chemical remained unidentified. Most of the components were isolated from the secretion of C. (L.) clathratus (nine), while the lowest number of compounds was found in C. (P.) gigas (two). Methacrylic acid was the most dominant compound by percentage in all five species, while angelic acid was also detected in all samples. As expected, salicylaldehyde was exclusively found in the species of the genus Calosoma Weber, 1801. The secretion of C. (P.) gigas was shown to achieve the highest level of antibacterial activity against Pseudomonas aeruginosa, Salmonella enterica, and S. typhimurium (even the same level as the positive control streptomycin), while the secretion of C. (C.) ulrichii achieved the highest antimicrobial potential against Staphylococcus epidermidis, S. aureus, Listeria monocytogenes, and Bacillus cer

In the present study, we investigated in vitro the antimicrobial activity of the pygidial gland secretion of the guanophilic ground beetle Laemostenus (Pristonychus) punctatus (Dejean, 1828) and some of its chemicals against resistant and non-resistant bacteria and Candida species, the synergistic and additive potential of combinations of selected chemicals and antimicrobial drugs against resistant bacterial and fungal strains, anti-adhesive and anti-invasive potential of the secretion and formic acid alone and in selected combinations with antimicrobial drugs against methicillin-resistant Staphylococcus aureus (MRSA) toward spontaneously immortalized human keratinocyte cell line (HaCaT cells). In addition, we examined the antiproliferative activity of the secretion and formic acid in vitro. The tested secretion and the standards of formic and oleic acids possessed a significant level of antimicrobial potential against all tested strains (P < 0.05). The isolate from guano Pseudomonas monteilii showed the highest resistance to the secretion and formic acid, while MRSA achieved a significantly high level of susceptibility to all agents tested, particularly to the combinations of formic acid and antibiotics, but at the same time showed a certain level of resistance to the antibiotics tested individually. Candida albicans and C. tropicalis were found to be the most sensitive fungal strains to the secretion. Formic acid (MIC 0.0005 mg/mL) and gentamicin (MIC 0.0010 mg/mL) in the mixture achieved synergistic antibacterial activity against MRSA (FICI = 0.5, P < 0.05). The combination of formic acid, gentamicin and ampicillin accomplished an additive effect against this resistant bacterial strain (FICI = 1.5, P < 0.05). The secretion achieved a better inhibitory effect on the adhesion ability of MRSA toward HaCaT cells compared to formic acid alone, while formic acid showed better results regarding the invasion (P < 0.001). The combinations of gentamicin and ampicillin, as

Introduction: A novel group of Rhizobiumspp. strains belonging to the “tumorigenes” clade has recently been described on blackberry in Serbia and Germany and on rhododendron in Germany. The BIOCTA project aimed to characterize efficient plant-associated bacterial strains for biocontrol of crown gall, thus providing an environmentally friendly alternative to pesticides that would contribute to the development of sustainable agriculture. Methods: Antagonistic potential of 37 biocontrol strains against two R. tumorigenes strains 932 and 1078 and Rhizobium sp. strain rho-6.2 was evaluated in vitro using the “well diffusion” method, as well as in vivo on tomato plants, using two inoculation strategies (co-inoculation and preventive). DNA metabarcoding approach was used to analyze the phytobiome of treated and non-treated tomato plants. Results: Based on the determined in vitro antagonistic potential, seven strains – Bacillus spp. (B. amyloliquefaciens ID084 and GT28.3, B. velezensis X5-2, and B. subtilis GD1), Pseudomonas sp. (R-6.10 and R11-20) and Agrobacterium rosae rho-6.1 were selected for further in vivo experiments. Of all tested strains/treatments, two Pseudomonas strains were the most efficient, showing up to 92.86%efficacy in suppressing tumors caused by Rhizobiumsp. strain rho-6.2 when applied in a co-inoculation strategy. Based on the DNA metabarcoding analysis, genera Pseudolabrys and Asanoa prevailed in the co-inoculation strategy, while Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium prevailed in positive control. Conclusion: Crown gall tumors have shown to be a valuable source of antagonistic isolates. Pseudomonas strains R-6.10 and R11-20 could be proposed for the efferent control of crown gall caused by newly described Rhizobium spp. strains in nurseries.

Targeted physiological groups of bacteria were cultivated and identified in the brackish groundwaters of Obrenovačka Banja (OB), Lomnički Kiseljak (LK) and Velika Vrbnica (VV) using biological activity reaction tests (BARTs) to assess the biocorrosion, biofouling and health risks. The highest density of iron-related, sulfate-reducing, slime-forming, facultatively anaerobic heterotrophic, denitrifying bacteria and representatives of Pseudomonas spp. was recorded in the OB sample, while the lowest density of the same physiological groups of bacteria was recorded in the LK sample. Facultatively anaerobic heterotrophic bacteria were the most abundant in the OB and LK samples, while, in contrast, heterotrophic aerobic bacteria were the most abundant in the VV sample. All tested samples were characterized by a high degree of biochemical activity associated with iron-related, sulfate-reducing, slime-forming, heterotrophic aerobic and facultatively anaerobic bacteria. Also, high biochemical activity of denitrifying bacteria was recorded in the OB sample, and the same activity of Pseudomonas species was recorded in the OB and VV samples. For OB and LK groundwaters, the highest degree of risk was estimated for biocorrosion process, while for the OB and VV occurrences, the highest degree of risk was estimated for biofouling process. The health risk was present for all examined groundwaters. Caution is warranted in further use of all investigated occurrences due to the established public health risk and an immediate revitalization of the OB, LK and VV wells is necessary.

Numerous microbial taxa are used as biofertilizers because they have the potential to competitively colonize the rhizosphere or root interior of plants and promote nutrient uptake. The aim was to investigate the shifts of keystone bacterial species in maize roots and rhizosphere during seedling stage, flowering, and harvest, under different treatments of bacterial phytobiotic (PHY), poultry manure (PM) and their combination (PHY_PM). Soil bacterial communities remained largely unchanged regardless of the treatment applied or phenophase studied, with uncultured Gaiellales and Bacillus being the most abundant. In contrast, bacterial communities in roots differed in terms of distribution and relative abundance (RA) of different taxa between growth stages and treatments. The most abundant bacterial taxa in the roots during the initial seedling stage was Pseudomonas. In the flowering, Bacillus occurred with a two- to threefold higher RA in treatments with PHY or PM compared to the negative control, while Lechevalieria dominated during the harvest. Differential abundance analysis at the seedling stage showed a reduction of Pseudomonas in roots treated with PHY, while Pseudonocardia was significantly more abundant in roots treated with PM than in the other samples. Massilia, Streptomyces, Lechevalieria, Microbacteriaceae, Aeromicrobium, Sphingomonas and Roseiflexaceae were significantly higher in the PHY_PM treated root samples. Steroidobacter and Bdellovibrio were absent in PHY and PM treated root samples during flowering, while Bdellovibrio was significantly reduced in PHY_PM treatment compared to the negative control. RA of Bradyrhizobium and Polaromonas was reduced in PHY treated root samples, and Dongia was completely absent. Gaiellales was significantly more abundant, while Sphingomonas was less abundant in roots treated with PM and PHY_PM. Solirubrobacter and Bdellovibrio were absent from roots during harvest in all three treatment types. Pajaroellobacter was comple

Soda pans are restricted to the Carpathian Basin and differ from other similar saline waters mainly due to the dominant presence of Na+, HCO3–, and CO32– ions. These shallow and temporary aquatic habitats are inhabited by a number of species that can thrive in extreme environments. In Serbia, saline habitats are rare, endangered, and most common in the territory of Vojvodina. One of the most investigated group of organisms in soda pans is diatoms. Due to ecophysiological plasticity, they can survive and tolerate extreme environmental conditions which gives them a competitive advantage over other algae. Quite the opposite, prokaryotes in saline habitats are not sufficiently studied and data are scarce. Thus, samples from 6 soda pans were collected in March 2021 aiming to determine diatom (microscopic and molecular analysis, 18S rRNA gene) and bacterial community (16S rRNA gene). Most of the recorded diatom taxa are neutrophilic to alkalibiontic, mostly halophilic, and eutrophic species. The species richness diversity index was the highest in Velika Slatina and Slatina, while it was lowest in Mala Rusanda. The genus Nitzschia was one of the most represented and numerous according to morphological analyses (24 taxa, 4 dominant), while molecular analyses indicate 11 different species with low abundances and mainly with unassigned sequences. The biggest discrepancy in these two approaches was observed in Mala Rusanda and Okanj bara. Metabarcoding analysis indicated Halamphora veneta as the dominant taxa, while morphological analyses have shown a predominance of Nitzschia supralitorea and Surirella brebissonii in Mala Rusanda, and N. austriaca in Okanj bara. Estimated richness and alpha diversity indices showed the highest bacterial diversity in Velika Rusanda and Okanj bara, while the lowest richness was in Mala Rusanda. Representatives of the phylum Proteobacteria were detected predominantly in Pečena Slatina, Bacteroidota in Velika Slatina, Actinobacteria in Okanj bara

INTRODUCTION Crown gall is an economically important and widespread plant disease caused by tumorigenic bacteria that are commonly affiliated with the genera Agrobacterium, Allorhizobium and Rhizobium. Novel and an atypical group of tumorigenic agrobacteria belonging to the genus Rhizobium (“tumorigenes” clade) was identified as a causative agent of crown/cane gall on blackberry, rhododendron and blueberry in Serbia and Germany (Kuzmanović et al., 2018 and 2019). Efficient measures to control crown gall disease were not reported till nowadays, so assessment and application of alternative biological control measures would contribute to sustainable agricultural production and environmental protection. The aims of the study were 1) identification of candidate bacterial strains that could be employed for biological control 2) to analyse phytobiome of the treated and non-treated crops and 3) to perform a whole-genome sequencing of a few most promising biocontrol strains. STATE OF THE ART Antimicrobial activity of ten biocontrol candidates from rhododendron and 27 additional antagonistic strains were tested in vitro against the tumor-inducing strain Rhizobium sp. rho-6.2. The six most efficient Pseudomonas and Bacillus strains were tested in vivo, using co-inoculation and preventive inoculation strategies in controlled greenhouse conditions on tomato plants as a model system in four replicas and randomized. Tumors from the most effective treatments were sampled, and then total DNA was isolated and subjected to the next-generation sequencing (NGS). Direct analysis of bacterial communities using Illumina MiSeq sequencing of 16S rRNA gene amplicon libraries was performed to assess the microbial ecological effect, with complete bioinformatic and computational biology analysis conducted. Also, a whole-genome sequencing of a few most promising antagonistic strains was performed. RESULTS Among six antagonistic strains, the most efficient in co-inoculation strategy against pathog

INTRODUCTION Maize is among the three world’s most important and widely grown cereals (Seyi-Amole & Onilude, 2021). The excessive and long-term application of agrochemicals for providing maize with essential nutrients, required for the development of all growth phenophases and for yield enhancement, leaves adverse consequences for human health and the environment (Khaliq et al., 2004). Although their use is inevitable to meet the increasing demand of the growing human population for a healthy food supply, organic fertilizers and biofertilizers (microbial fertilizers) are becoming recognized as effective, economically feasible, and environmentally sound alternatives for sustainable agriculture (Lawal & Babalola, 2014; Hui et al., 2017; Mahanty et al., 2017). The main objective of this study was to evaluate the influence of the microbial inoculant Phytobiotic (PHY), containing a consortium of Bacillus subtilis sp. subtilis and Microbacterium sp., on native maize microbiome during key growth phenophases (seedling, flowering, and harvesting) under field conditions, as well as to compare whether differences in efficacy between PHY, poultry manure (PM) and their combination (PHY_PM) exist, based on yield parameters. STATE OF THE ART Seeds, roots, and soil samples were taken for metabarcoding analysis during four growth phenophases (I-IV). Samples of uninoculated seeds and soil, poultry manure, and seeds inoculated with PHY were primarily taken before sowing (phenophase I). Further, during the growing season [phenophases II (seedling), III (flowering), and IV (harvesting)] the effect of PHY, PM, and PHY_PM on maize seeds, roots, and soil microbiome was evaluated in relation to concurrently sampled negative controls. A total DNA from the collected samples was isolated, amplified with primers 515F/ 806R targeting the V4 region of the 16S rRNA, and subjected to next-generation sequencing (NGS). The obtained sequence data were bioinformatically processed and used for the evalu

BACKGROUND Atypical Rhizobium sp. were identified as a causative agent of crown gall on rhododendron and blueberry in Germany. Considering the lack of efficient measures against crown gall disease, evaluation of innovative biocontrol measures would greatly contribute to sustainable agriculture. OBJECTIVES Identification of candidate bacterial strains that could be employed for biological control of the novel crown gall bacteria belonging to the ″tumorigenes″ clade. METHODS Antimicrobial activity of six antagonistic Pseudomonas and Bacillus strains were tested in vitro and in vivo against pathogenic strain Rhizobium sp. rho-6.2. The in vivo experiment, using co-inoculation and preventive inoculation strategies, was performed in controlled greenhouse conditions on tomato plants as a model system in four replicas and randomized. RESULTS The whole cultures of two antagonistic Pseudomonas strains were the most efficient against pathogenic Rhizobium sp. rho-6.2 in co-inoculation strategy with reducing tumor size of 92.86%. Contrary, in the preventive treatment same Pseudomonas strains were less efficient (15.38 and 30.77%). Despite the high in vitro antimicrobial activity of Bacillus strains their in vivo activity was less pronounced in preventive treatment (up to 15.38%), while in co-inoculation strategy was more prominent (42.86%). Consortium based on Bacillus and Pseudomonas strains, was increased biocontrol activity up to 38.6% of tumor’s reduction. The selected Pseudomonas strains could be further tested as an alternative strategy for the biocontrol of crown gall disease and potential involvement of quorum quenching mechanism will be determined.

The potential of two biocontrol strains, Bacillus velezensis X5-2 and Pseudomonas orientalis X2-1P to control black rot caused by Xanthomonas campestris pv. campestris was evaluated in vivo on autochthonous cabbage cultivar ‘Futoški’, under the condition of natural infection. Liquid formulations of biocontrol strains were prepared in fermenters (B. velezensis - 1010 CFU mL-1, P. orientalis - 109 CFU mL-1) and diluted with water in a 1:5 ratio, before use. Treatments were performed with each strain and their mixture (1:1). The experiment included the following: (i) seed treatments (15, 30, 60 min), (ii) foliar treatments (three treatments: when the first symptoms appeared and remaining every two weeks), and (iii) combined seed and foliar treatments. Experiments were conducted in four replicates, with 10 plants per replicate. Two controls were used, untreated and conventionally treated cabbage (pesticides). Assessment of disease intensity was rated one month after the last foliar treatment, using the Horsfall-Barratt scale (1-12). During ripening, cabbage heads’ weights were measured and data were statistically processed (Minitab). All performed treatments were effective in the control of black rot (85.7-98.9%). The highest efficacy was obtained in combined seed (60 min) and foliar treatments with P. orientalis, as well as its mixture with B. velezensis (98.9% both). All treatments influenced the increase of cabbage heads’ weight (up to 1.3 times), with the highest found in combined treatments (60 min seed + foliar) using a mixture of B. velezensis and P. orientalis. A negative correlation (P≤0.05) was found between disease intensity and cabbage heads’ weight.

Maize (Zea mays L.) occupies a significant part of the world cultivated area. Beneficial microorganisms and organic fertilizers are powerful tools for sustainable agricultural management. Applying appropriate formulation either through seed coating or composting material together with seeds during the sowing was aimed to achieve optimal performance on plants and increase the crop yields. Also, a complete analysis of phytobiome including high-throughput amplicon and whole-genome sequencing, and computational biology of the treated and non-treated plants' roots and soil was applied. The statistically significant difference in bacterial communities between phenophases and treatments was much more prevalent in the roots than soil itself. In general, seedling phenophase (II) differed in terms of diversity from bacterial communities of flowering (III) and harvesting phenophases (IV), regardless of treatment, indicating good colonization with the treated substrate for up to one month. In the root samples, the dominance of the genus Pseudomonas was evident, in the initial stages (phase II), while this percentage decreased linearly over time. High relative abundance of the genera Achromobacter, Sphingobacterium, and Stenotrophomonas also characterized II phenophase. Contrary, a relative abundance of the genus Bacillus was characteristic for III phenophase, and especially twice or three times higher in treatments with phytobiotic or manure compared to the negative control. Furthermore, it was observed that with increasing inoculation of Bacillus isolate, the percentage of Pantoea genus decreases drastically in coated seeds. In conclusion, a statistically significant increase in maize yield was obtained in the treatment with phytobiotic with an average value of 650 kg/ha compared to the negative control.

The olive tree is one of the most important agricultural plants, affected by several pests and diseases that cause a severe decline in health status leading to crop losses. Olive leaf spot disease caused by the fungus Venturia oleaginea can result in complete tree defoliation and consequently lower yield. The aim of the study was to obtain new knowledge related to plant–pathogen interaction, reveal mechanisms of plant defense against the pathogen, and characterize fungal phyllosphere communities on infected and symptomless leaves that could contribute to the development of new plant breeding strategies and identification of novel biocontrol agents. The highly susceptible olive variety “Istrska Belica”' was selected for a detailed evaluation. Microscopy analyses led to the observation of raphides in the mesophyll and parenchyma cells of infected leaves and gave new insight into the complex V. oleaginea pathogenesis. Culturable and total phyllosphere mycobiota, obtained via metabarcoding approach, highlighted Didymella, Aureobasidium, Cladosporium, and Alternaria species as overlapping between infected and symptomless leaves. Only Venturia and Erythrobasidium in infected and Cladosporium in symptomless samples with higher abundance showed statistically significant differences. Based on the ecological role of identified taxa, it can be suggested that Cladosporium species might have potential antagonistic effects on V. oleaginea. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.

Šljiva (Prunus domestica L.) ima izuzetan značaj kao voćarska kultura u Srbiji i tradicionalno se prerađuje u rakiju šljivovicu. S obzirom da je godišnji prinos šljive ugrožen različitim bolestima, naročito izazivačima bakterioznog raka i mrke truleži neophodno je naći efikasne agense za njihovo suzbijanje, a naročito alternativu upotrebi hemijskih pesticida. U ovom radu je prvi put analiziran mikrobiom filosfere četiri sorte šljive (Čačanska lepotica, Čačanska rodna, Požegača i Ranka), obuhvatajući ranu (maj) i kasnu fenološku fazu (juli) razvića ploda. Indeksi alfa i beta diverziteta su pokazali da su zajednice bile heterogene i da je njihov sastav zavisio od sezone uzorkovanja i sorti šljive. U ukupnoj bakterijskoj zajednici je metagenomskim pristupom utvrđeno da su predstavnici razdela Proteobacteria bili najdominantniji, a najzastupljenije vrste su bile iz rodova: Methylobacterium, Sphingomonas i Hymenobacter. Tradicionalnim kultivabilnim pristupom i analizom sekvenci gena za 16S rRNK identifikovane su Pseudomonas syringae i Pseudomonas graminis kao najdominantnije vrste. Analiza mikobioma je ukazala na dominatnu zastupljenost predstavnika razdela Ascomycota. Vrste iz rodova Aureobasidium i Cryptococcus su bile najučestalije u maju, dok su u julu predstavnici različitih rodova dominirali na sortama šljive (Cryptococcus, Metschnikowia, Fusarium i Hanseniaspora). U okviru kolekcije kultivabilnih gljiva, identifikovano je 11 izolata Monilinia laxa na osnovu filogenetske analize sekvenci ITS regiona. Odabrani izolati M. laxa su prouzrokovali tipične simptome na ubranim plodovima sorti Požegača i Čačanska rodna, a testiranjem potencijalnih bakterijskih patogena su izdvojeni izolati P. syringae ČL2/2 i P7/16_2, koji su izazivali nekroze na ubranim listovima šljive svih ispitivanih sorti. Analizom antagonističkog potencijala kolekcije bakterija i kvasaca poreklom sa sve četiri sorte je izdvojen izolat Bacillus thuringiensis R3/3 sa snažnom antibakterijskom aktivnošću, Plum (Prunus domestica L.) has a great importance as a fruit crop in Serbia and it is traditionally processed into slivovitz brandy. Considering that the annual plum yield is significantly affected by various pathogens, especially those causing bacterial canker and brown rot, it is necessary to find effective agents for their control, and in particular, an alternative to the chemical pesticides. In this research, microbiome of four plum cultivars phyllosphere (Čačanska lepotica, Čačanska rodna, Požegača i Ranka) was analyzed for the first time, including the early (May) and late phenological stages (July) of fruit development. Alpha and beta diversity indices had shown that the communities were heterogenous and that their composition depended on sampling season and plum cultivars. The metagenomic approach revealed that the representatives of the phylum Proteobacteria were the most dominant in the total bacterial community, and that the most represented species were from the genera: Methylobacterium, Sphingomonas and Hymenobacter. Traditional cultivable approach and 16S rRNA sequence analyses identified Pseudomonas syringae i Pseudomonas graminis as two most dominant species. Mycobiome analysis revealed the dominance of the phylum Ascomycota representatives. Aureobasidium and Cryptococcus species were the most abundant in May, while in July representatives of different genera dominated the plum cultivars (Cryptococcus, Metschnikowia, Fusarium and Hanseniaspora). From the collection of cultivable fungi, eleven Monilinia laxa isolates were identified based on phylogenetic analysis of the ITS region sequences. The selected M. laxa isolates caused typical symptoms on the harvested fruits of the Požegača and Čačanska rodna cultivars, and the testing of potential bacterial pathogens revealed P. syringae ČL2/2 and P7/16_2 isolates, which caused necrosis on the harvested plum leaves of all tested cultivars. Antagonistic potential analysis of bacterial and yeast isolates from

European plum (Prunus domestica L.) is a significant commercial crop in Serbia in terms of total fruit production, and is traditionally processed into slivovitz brandy. The brown rot disease caused by Monilinia laxa drastically reduces plum yield almost every year. Fungal communities associated with leaves and fruits of four local Serbian plum cultivars (Požegača, Ranka, Čačanska Lepotica and Čačanska Rodna) were investigated in two phenological stages during early (May) and late (July) fruit maturation. Alpha diversity indices showed that fungal communities were heterogeneous and Beta diversity indicated that autochthonous fungal communities depended upon seasonal changes and the cultivars themselves. The phylum Ascomycota was the most abundant in all samples, with relative abundance (RA) between 46% in the Požegača cultivar (May) and 89% in the Lepotica cultivar (July). The most abundant genus for all plum cultivars in May was Aureobasidium, with RA from 19.27 to 33.69%, followed by Cryptococcus, with 4.8 to 48.80%. In July, besides Cryptococcus, different genera (Metschnikowia, Fusarium, and Hanseniaspora) were dominant on particular cultivars. Among all cultivable fungi, molecular identification of eleven M. laxa isolates from four plum cultivars was performed simultaneously. Bacterial isolates from the plum phyllosphere were tested for their potential antifungal activity against indigenous M. laxa isolates. The most potent antagonist P4/16_1, which significantly reduced mycelial growth of M. laxa, was identified as Pseudomonas synxantha. Further characterization of P4/16_1 revealed the production of volatile organic compounds and phenazine-1-carboxylic acid (PCA). Crude benzene extract of PCA exhibited 57–63% mycelial growth inhibition of M. laxa. LC/MS analysis of the crude extract confirmed the presence of phenazine derivatives amongst other compounds. Scanning electron microscopy revealed morpho-physiological changes in the hyphae of M. laxa isolates caused