Biocontrol Agents Of Plant Pathogens Research Articles

Assessment of the Protective Potential of Inoculums and Metabolites of Rhizobacteria on Soybean (Glycine max) Seedlings against Bacterial and Fungal Pathogens.

Plant growth-promoting bacteria (PGPR), while generally considered to aid plant growth with the provision of nutrients, can also be used as biocontrol agents for plant pathogens. The study assessed the protective potential of inoculums and metabolites of plant growthpromoting rhizobacterial strains against bacterial and fungal pathogens on soybean seedlings. Inoculums and metabolites of 15 rhizobacterial strains were used for the study. Five pathogens (Alternaria sp., Aspergillus niger, Corynespora sp., Fusarium oxysporum and Xanthomonas campestris) were employed for the study. Four experimental setups: treated-only seeds, infected-only seeds, infected then inoculum or metabolite treated seeds, and infected then distilled water treated seeds. In the setup infected with Alternaria sp., final germination values of seeds in the presence of the respective inoculums showed no significant variation between the treated only and the infected then treated setup. In the case of seeds infected with Aspergillus niger, higher germination and vigor index values were observed in the treated-only seeds when compared with the infected then-treated seeds. For seeds infected with Corynespora sp., significantly lower germination and vigor index values were observed in the infected then-treated seeds than the treated-only seeds in the presence of the respective inoculums. With regards to setup infected with Fusarium oxysporum, significantly higher final germination and vigor index values were recorded for the treated only seeds when compared with the infected then treated setups. For the Xanthomonas campestris infected seeds, the majority of the infected then metabolite-treated seeds showed significantly lower final germination values when compared with the treated-only seeds. The study findings were able to establish the efficacy of some bacteria agents against economically important species of plant pathogens.

Antibacterial Activity of Different Strains of the Genus Trichoderma

The main pathogens causing plant diseases are bacteria, viruses, and fungi. A number of strategies are usually used for plant protection and control of pathogenic microorganisms. The main interest of researchers is focused on the development of alternative synthetic chemicals to control bacterial diseases of plants. Among such approaches, biological control of bacterial diseases using agents such as antagonistic fungi and some other microorganisms is considered to be one of the most effective strategies. Species of the genus Trichoderma are known for their antagonistic activity against plant pathogenic fungi and bacteria and can be an effective safety strategy to control them. An important peculiarity of fungi of this genus is their ability to inhibit target pathogenic organisms without harming non-target (beneficial) microorganisms. The study of the antagonistic activity of fungi of the genus Trichoderma was conducted mainly against pathogenic fungi of agricultural plants. At the same time, the study of the antibacterial activity of fungi of this genus has attracted much less attention. Therefore, the aim of our work was to determine the antibacterial activity of microscopic fungi of the genus Trichoderma against test cultures of bacteria causing pathogenesis of agricultural plants. Methods. The objects of research were 100 fungal strains of the genus Trichoderma and six economically important plant pathogenic bacteria such as Pseudomonas syringae UCM В-1027Т, Pseudomonas fluorescens 8573, Pectobacterium carotovorum UCM В-1095T, Xanthomonas campestris pv. campestris UCM В-1049, Clavibacter michiganensis subsp. michiganensis 102, and Agrobacterium tumefaciens UCM В-1000. Cultures of the studied fungi were grown on potato-dextrose agar. The antagonistic activity of fungi of the genus Trichoderma against plant pathogenic bacteria was studied using the conventional method of diffusion in agar and method of dual culture. The antibacterial activity of culture filtrates of Trichoderma strains was evaluated via the zone of growth inhibition of plant pathogenic bacteria. The percentages of growth inhibition of plant pathogenic bacteria were calculated, and the antagonistic activity of strains was concluded on the basis of the obtained values. Results. In general, the studied Trichoderma strains had the antagonistic activity against plant pathogenic bacteria. Using method of diffusion in agar, it was shown that among the 100 studied Trichoderma strains, 12 had the effect of growth inhibition (bacteriostatic effect) of all six studied species of pathogenic bacteria; 20 strains inhibited the growth of five ones, 36 — four, 12 — three, and 7 — of two strains. The strains with a wide spectrum of antibacterial activity were studied by the double culture method. This made it possible to demonstrate the high selectivity of the antagonistic effect of Trichoderma strains on individual test cultures of phytopathogenic bacteria. For example, strain No7A inhibited the growth of C. michiganensis subsp. michiganensis 102 by 47% and the growth of P. syringae UCM B-1027T by 30%, while the zones of growth inhibition of these test cultures, determined by the method of diffusion in agar, were 5 and 6 mm, respectively. Conclusions. The obtained results indicated the potential and overall ability of Trichoderma strains to biologically control bacterial pathogens. The most promising for the use of plant pathogenic bacteria as agents for biocontrol were strains F-60, 1515, and 320, which were active against all studied bacteria. Such strains may have the potential as a preventive biocontrol agent of plant pathogens with a wide range of action. On the other hand, Trichoderma strains with high activity against certain pathogens may have the potential to be used as a control agent against a specific target pathogen.

N -acylhomoserine lactone-degrading activity of Trichoderma species and its application in the inhibition of bacterial quorum sensing.

Many gram-negative pathogens can activate virulence factors under the control of N-acylhomoserine lactone (AHL）-mediated quorum sensing. AHL-degrading enzymes have been investigated for their application in disease control. Trichoderma is a genus of fungi inhabiting various types of soil and are widely used as biocontrol agents for plant pathogens. When the AHL-degrading activity of 33 strains belonging to Trichoderma species was investigated, most strains can degrade AHL. AHL lactonase catalyzes AHL ring opening by hydrolyzing lactone. Two model strains, Trichoderma atroviride MAFF 242473 and MAFF 242475, degrade AHL using their AHL lactonase activity and rapidly metabolize ring-opening AHL. Moreover, co-inoculation with MAFF 242473 and MAFF 242475 effectively inhibited AHL production by the plant pathogens, Pantoea ananatis and Pectobacterium carotovorum subsp. carotovorum. Our study suggested that Trichoderma might be an effective biocontrol agent to inhibit the expression of virulence factors via AHL-mediated quorum sensing.

Selecting Endophytes for Rhizome Production, Curcumin Content, Biocontrol Potential, and Antioxidant Activities of Turmeric (Curcuma longa).

Beneficial endophytes may enhance plant growth and stress tolerance. Yet, the plant health benefits of endophytes can be altered by biotic and abiotic factors and, thus, favour the inhibition of turmeric growth and curcumin production. The double petri dish method and greenhouse pot experiments were conducted to assess the biocontrol potential and impact of endophytes on the output, curcumin levels, and antioxidant activities of turmeric (Curcuma longa L.). The results showed that endophytes could control some disease-causing plant pathogens: 52% of all isolates have an antagonistic action against Fusarium oxysporum, 43% against Pythium myriotylum, 35% against Phytophthora megakarya, and 56% against Ralstonia solanacearum in vitro. Eight months after sowing, most endophyte isolates can increase the yield of turmeric rhizomes on a sterile substrate after inoculation, with yields ranging from 42 to 105% higher than the control and 3 to 50% higher than the urea treatment. In addition, 52% endophytes isolate significantly raised curcumin levels after 8 months of culture (from 2.1 to 3.1%) compared to control (1.7%) and urea treatment (1.8%). These endophytes promote an increase in the levels of reduced glutathione (22%), total thiols (26%), and carotenoids (91%) in turmeric. The study concludes that, in general, the endophytes-turmeric association can stimulate turmeric rhizome production, curcumin, and the antioxidant activities of the plant. They can also be used as biocontrol agents for plant pathogens.

Community Analysis of Culturable Sapwood Endophytes from Apulian Olive Varieties with Different Susceptibility to Xylella fastidiosa

Endophytes are symptomless fungal and/or bacterial microorganisms found in almost all living plant species. The symbiotic association with their host plants by colonizing the internal tissues has endowed them as a valuable tool to suppress diseases, stimulate growth, and promote stress resistance. In this context, the study of culturable endophytes residing the sapwood of Apulian olives might be a promising control strategy for xylem colonizing pathogens as Xylella fastidiosa. To date, olive sapwood cultivable endophytes are still under exploration; therefore, this work pursues a study of cultivable endophytes occurrence variation in the sapwood of different olive varieties under the effect of seasonality, geographical coordinates, and X. fastidiosa infection status. Our study confirms the stability of sapwood endophytic culturable communities in the resistant olive variety and presents the seasonal and geographical fluctuation of olive trees’ sapwood endophytes. It also describes the diversity and occurrence frequency of fungal and bacterial genera, and finally retrieves some of the sapwood-inhabiting fungal and bacterial isolates, known as biocontrol agents of plant pathogens. Thus, the potential role of these bacterial and fungal isolates in conferring olive tree protection against X. fastidiosa should be further investigated.

Genomics, proteomics and transcriptomics in the biological control of plant pathogens: a review

Plant diseases cause significant yield and quality losses and thereby need to be minimized. Several approaches can be used to manage plant diseases. Farmers often depend more on chemical fertilizers and pesticides, in addition to good agronomic practices. Excessive use of agrochemicals has led to environmental pollution. Natural biocontrol agents have been postulated to be less harmful; however, despite successful identification of several biocontrol agents, inefficacy and inconsistency against specific plant diseases under different field and environmental conditions has been shown to be a big obstacle. This emphasizes the need for improved biocontrol agents which can withstand adverse conditions and still perform well for management of diseases caused by pathogens. Genome sequencing of biocontrol organism can provide better insights for effective management of plant diseases. Besides these, omics-technology based knowledge is increasingly contributing to better understanding of biocontrol strategies. While genetically modified microorganisms can play an important role, regulatory concerns can hamper effective commercialization. In this scenario, the omics-based technologies are expected to play a major role in future commercialization of biocontrol agents. This review provides an overview of the evolution of genomics, proteomics, and transcriptomics in the field of biocontrol agents for plant pathogens.

Culture-Dependent and Culture-Independent Characterization of the Olive Xylem Microbiota: Effect of Sap Extraction Methods.

Microbial endophytes are well known to protect host plants against pathogens, thus representing a promising strategy for the control of xylem-colonizing pathogens. To date, the vast majority of microbial communities inhabiting the olive xylem are unknown; therefore, this work pursues the characterization of the xylem-limited microbiome and determines whether the culture isolation medium, olive genotype, and the plant material used to analyze it can have an effect on the bacterial populations retrieved. Macerated xylem tissue and xylem sap extracted with the Scholander chamber from olive branches obtained from two cultivated and a wild olive genotypes were analyzed using culture-dependent and -independent approaches. In the culture-dependent approach using four solid culture media, a total of 261 bacterial isolates were identified after performing Sanger sequencing of 16S rRNA. Culturable bacteria clustered into 34 genera, with some effect of culture media for bacterial isolation. The cultivated bacteria belonged to four phyla and the most abundant genera included Frigoribacterium (18.8%), Methylobacterium (16.4%), and Sphingomonas (14.6%). On the other hand, in the culture-independent approach conducted using Illumina MiSeq 16S rRNA amplicon sequencing [next-generation sequencing (NGS)] of the xylem extracts, we identified a total of 48 operational taxonomic units (OTUs) belonging to five phyla, being Sphingomonas (30.1%), Hymenobacter (24.1%) and Methylobacterium (22.4%) the most representative genera (>76% of reads). In addition, the results indicated significant differences in the bacterial communities detected in the xylem sap depending on the genotype of the olive tree studied and, to a minor extent, on the type of sap extraction method used. Among the total genera identified using NGS, 14 (41.2%) were recovered in the culture collection, whereas 20 (58.8%) in the culture collection were not captured by the NGS approach. Some of the xylem-inhabiting bacteria isolated are known biocontrol agents of plant pathogens, whereas for others little information is known and are first reported for olive. Consequently, the potential role of these bacteria in conferring olive tree protection against xylem pathogens should be explored in future research.

Transcriptome and Metabolome Reprogramming in Tomato Plants by Trichoderma harzianum strain T22 Primes and Enhances Defense Responses Against Aphids.

Beneficial fungi in the genus Trichoderma are among the most widespread biocontrol agents of plant pathogens. Their role in triggering plant defenses against pathogens has been intensely investigated, while, in contrast, very limited information is available on induced barriers active against insects. The growing experimental evidence on this latter topic looks promising, and paves the way toward the development of Trichoderma strains and/or consortia active against multiple targets. However, the predictability and reproducibility of the effects that these beneficial fungi is still somewhat limited by the lack of an in-depth understanding of the molecular mechanisms underlying the specificity of their interaction with different crop varieties, and on how the environmental factors modulate this interaction. To fill this research gap, here we studied the transcriptome changes in tomato plants (cultivar “Dwarf San Marzano”) induced by Trichoderma harzianum (strain T22) colonization and subsequent infestation by the aphid Macrosiphum euphorbiae. A wide transcriptome reprogramming, related to metabolic processes, regulation of gene expression and defense responses, was induced both by separate experimental treatments, which showed a synergistic interaction when concurrently applied. The most evident expression changes of defense genes were associated with the multitrophic interaction Trichoderma-tomato-aphid. Early and late genes involved in direct defense against insects were induced (i.e., peroxidase, GST, kinases and polyphenol oxidase, miraculin, chitinase), along with indirect defense genes, such as sesquiterpene synthase and geranylgeranyl phosphate synthase. Targeted and untargeted semi-polar metabolome analysis revealed a wide metabolome alteration showing an increased accumulation of isoprenoids in Trichoderma treated plants. The wide array of transcriptomic and metabolomics changes nicely fit with the higher mortality of aphids when feeding on Trichoderma treated plants, herein reported, and with the previously observed attractiveness of these latter toward the aphid parasitoid Aphidius ervi. Moreover, Trichoderma treated plants showed the over-expression of transcripts coding for several families of defense-related transcription factors (bZIP, MYB, NAC, AP2-ERF, WRKY), suggesting that the fungus contributes to the priming of plant responses against pest insects. Collectively, our data indicate that Trichoderma treatment of tomato plants induces transcriptomic and metabolomic changes, which underpin both direct and indirect defense responses.

Eurypsychrophilic Pseudomonas spp. isolated from Venezuelan tropical glaciers as promoters of wheat growth and biocontrol agents of plant pathogens at low temperatures

Andean tropical glaciers are disappearing rapidly and, consequently, the microbes immured in these frozen environments will be lost forever. Some of these microbes are thought to be potentially useful to develop biotechnological products or processes. Among these microbes, plant-growth promoting (PGP) bacteria have been proposed as valuable tools to develop cold-active biofertilizers and/or biopesticides. A few years ago, we hypothesized that bacteria immured within glacial ice could be effective in promoting plant growth and/or in protecting plants from pathogen infection, at low temperatures. In this study, we aimed at testing some of these traits, with a suitable plant model (Triticum aestivum). In the present study, from a collection of bacteria isolated from Venezuelan tropical glaciers, we selected four Pseudomonas isolates and tested their PGP effects at low temperatures, both in vitro and on wheat plantlets. The isolates grew well over a wide range of low temperatures and were thus classified as eurypsychrophilic. They also displayed well-known PGP traits: solubilization of inorganic phosphates, production of phytohormones and antagonism against a phytopathogenic oomycete (Pythium ultimum). Inoculation of T. aestivum seeds with some of these Pseudomonas spp. isolates promoted a significant elongation of their roots and shoots. This was also the case when wheat plantlets were grown in sterile sand or soil, at 15 °C. Inoculation of wheat seeds also protected plantlets against the damage caused by P. ultimum. Together, our results suggest that some of these Pseudomonas spp. isolates could act as cold-active biofertilizers and/or biocontrol agents.

Purification and characterization of alkaline protease produced by Streptomyces flavogriseus and its application as a biocontrol agent for plant pathogens

Background A protease is an enzyme that helps proteolysis: protein catabolism by hydrolysis of peptide bonds. Proteases were the first enzymes to be commercialized, partly on the account of the history of availability and on account of need. Aim The aim of the present work is studying the properties of the partially purified enzyme and some application of the enzyme. Materials and methods In this study, alkaline protease was produced by Streptomyces flavogriseus using the shaking method. The enzyme was partially purified by ammonium sulfate precipitation. The most active fraction was evaluated on Sephadex G-100 column chromatography. The activity of the enzyme was determined at different temperatures and different pH values using various buffers. Results and conclusion In this study, alkaline protease produced by S. flavogriseus was partially purified by ammonium sulfate precipitation at 75% w/v saturation and pooled on Sephadex G-100 with a yield of 60.85% and specific activity of 85.14 U/mg protein. The enzyme was optimally active at 45°C in 0.5 mol/l potassium phosphate buffer (pH 8.0) after 30 min of incubation and was broadly stable at 45°C for 60 min and pH 6–8. The alkaline protease relative activity was increased in the presence Mn2+, Co2+, K+, Na+, Fe2+, and Mg2+ at concentration 1 mmol/l, respectively.

Immobilization of Bacteriocins from Lactic Acid Bacteria and Possibilities for Application in Food Biopreservation

Bacteriocins are biologically active compounds produced by a large number of bacteria, including lactic acid bacteria (LAB), which exhibit antimicrobial activity against various saprophytic and pathogenic microorganisms. In recent decades, bacteriocins are increasingly becoming more important in different branches of the industry due to their broad antibacterial and antifungal spectrum - in the food industry for natural food preservation and expiry date extension; in the health sector for preparation of probiotic foods and beverages; in the clinical practice as alternatives of conventional antibiotics; in the agriculture as biocontrol agents of plant pathogens and alternatives of chemical pesticides for plant protection. The broad antimicrobial spectrum of bacteriocins has stimulated the research attention on their application mainly in the food industry as natural preservatives. Most scientific achievements concerning the application food biopreservation are related to bacteriocins produced by LAB. The lactic acid bacteria bacteriocins can be produced in the food substrate during its natural fermentation or can be added in the food products after obtaining byin vitrofermentations under optimal physical and chemical conditions. Moreover, the immobilization of LAB bacteriocins on different matrices of organic and inorganic origin has been proposed as an advanced approach in the natural food preservation for their specific antimicrobial activity, anti-biofilm properties and potential use as tools for pathogen detection.

Lsp family proteins regulate antibiotic biosynthesis in Lysobacter enzymogenes OH11

Ax21 family proteins have been shown to play regulatory roles in plant- and animal-pathogenic species in the bacterial family Xanthomonadaceae, but the protein have not been investigated previously in the non-pathogenic members of this bacterial family. Lysobacter enzymogenes, is a non-pathogenic species known for its capacity as a biocontrol agent of plant pathogens. It is also noted for the production of antimicrobial secondary metabolites, heat stable antifungal factor (HSAF) and WAP-8294A2, that have potential for agricultural and pharmaceutical applications. The species also displays type IV pili-dependent twitching motility and the production of multiple extracellular lytic enzymes as additional biocontrol-related traits. Here, we show that L. enzymogenes strain OH11 possesses three genes widely separated in the OH11 genome that code for unique Ax21-like proteins (Lsp). By comparing the wildtype OH11 with mutant strains having a single lsp gene or a combination of lsp genes deleted, we found that each Lsp protein individually is involved in positive regulation of HSAF and WAP-8294A2 biosynthesis, but the proteins collectively do not exert additive effects in this regulation. None of the Lsp proteins were found to influence twitching motility or the production of three extracellular lytic enzymes. This study is the first to provide evidence linking Ax21-family proteins to antibiotic biosynthesis and, hence, adds new insights into the diversity of regulatory functions of Ax21 family proteins in bacteria.

The transcription factor SKN7 regulates conidiation, thermotolerance, apoptotic-like cell death and parasitism in the nematode endoparasitic fungus Hirsutella minnesotensis.

The transcription factor SKN7 is a highly conserved protein among fungi and was initially recognized as a response regulator that protects cells from oxidative stress and maintains cell wall integrity in yeast. Orthologs of SKN7 are extensively present in biocontrol agents of plant pathogens, but they had not been functionally characterized. Here, we identified and characterized the transcription factor SKN7 in the nematode endoparasitic fungus Hirsutella minnesotensis. Null mutant lacking HIM-SKN7 (HIM_03620), which was generated by a gene disruption strategy, demonstrated reduced conidiation, increased sensitivity to high temperature, hydrogen peroxide, mannitol and ethanol, and reduced fungal resistance to farnesol. However, over-expression mutant showed increased conidial production, thermotolerance and resistance to farnesol, suggesting that HIM-SKN7 regulates antiapoptotic-like cell death in H. minnesotensis. Moreover, the results showed that in null mutant, H. minnesotensis had decreased endoparasitic ability as compared to wild type and over-expression strain. During the infection process, the relative expression of the HIM-SKN7 gene was significantly induced in the wild type and over-expression strain. The results of the present study advance our understanding of the functions of the SKN7 gene in biocontrol agents, in particular, nematode endoparasitic fungi.

Streptomycesspp. alleviateRhizoctonia solani-mediated oxidative stress inSolanum lycopersicon

The ability of Streptomyces species to act as biocontrol agents for plant pathogens via induced systemic resistance has been demonstrated and considerable efforts have been made in elucidating the underlying mechanisms of Streptomyces–host plant–phytopathogen interactions. Here, we have assessed the ability of Streptomyces coelicolor, Streptomyces griseus, Streptomyces albus, Streptomyces antibioticus and Streptomyces champavatii to provide disease protection against Rhizoctonia solani in Solanum lycopersicon and have also examined associated changes in hydrogen peroxide (H2O2) production, lipid peroxidation (LPO) and antioxidant enzymes. The production of H2O2 at the second day after pathogen inoculation (dapi) was observed to be 1.1-fold higher in Streptomyces-treated plants, when compared to untreated inoculated control plants. A similar increase in catalase and ascorbate peroxidase activity was observed at fourth dapi whereas increased activities of guaiacol reductase and glutathione peroxidase were observed at fifth dapi. Likewise, LPO reached a maximum at sixth dapi in untreated inoculated plants while in Streptomyces-treated plants it was observed to be 1.3–1.5-fold less when compared to untreated inoculated control plants. This study offers novel insights into the mechanisms of priming by Streptomyces and highlights their capacity to activate plant defence responses generated by biotic stress through induction of antioxidant enzymes along with improved reactive oxygen species management.

Bahasa Indonesia

Nursery disease frequently found on Acacia crassicarpa seedlings is bacterial leaf blight caused by Xanthomonas sp. Disease symptom starts as a small fleck on the leaf which may then develop to leaf strike or leaf blight if the environmental factors are conducive to disease development. Actinomycetes are soil microorganisms that produce biologically active substances such as enzymes and antibiotics. These compounds could inhibit growth of other microorganisms, particularly bacteria. Thus, Actinomycetes are considered as potential candidates of biocontrol agents for plant pathogens. In the current study Actinomycetes isolated from a wide range of localities were screened for their efficacy against Xanthomonas sp. in vitro. The objective of this study was to obtain Actinomycete isolates effective against Xanthomonas, to mitigate impact of the pathogen on quality of A. crassicarpa seedlings. All Actinomycete collections were isolated from soil by a chain of enrichment isolation procedures. The antibiotic activities were investigated through antimicrobial screening tests using paper discs on assay plates. Of the 75 Actinomycete isolates originally collected and screened, 5 isolates showed good antimicrobial activities against Xanthomonas and are therefore considered as potential biocontrol agent candidates.

Purification of an Antifungal Endochitinase from a Potential Biocontrol Agent Streptomyces griseus

Streptomyces griseus (MTCC 9723) is a chitinolytic bacterium isolated from prawn cultivated pond soil of Peddapuram Village; East Godavari District was studied in detailed. Chitinase (EC 3.2.1.14) was extracted from the culture filtrate of Streptomyces griseus and purified by ammonium sulfate precipitation, DEAE-cellulose ionexchange chromatography, Sephadex G-100 and Sephadex G-200 gel filtration chromatography. The molecular mass of the purified chitinase was estimated to be 34, 32 kDa by SDS gel electrophoresis and confirmed by activity staining with Calcofluor White M2R. Chitinase was optimally active at pH of 6.0 and at 40 degrees C. The enzyme was stable from pH 5-9 and up to 20-50 degrees C. The chitinase exhibited Km and Vmax values of 400 mg and 180 IU mL(-1) for colloidal chitin. Among the metals and inhibitors that were tested, the Hg+, Hg2+ and P-chloromercuribenzoic acid completely inhibited the chitinase activity at 1 mM concentration. The purified chitinase showed high activity on colloidal chitin, chitobiose, and chitooligosaccharide. An in vitro assay proved that the crude chitinase, actively growing cells of S. griseus having antifungal activity against all studied fungal pathogen. This result implies that characteristics of S. griseus producing endochitinase made them suitable for biotechnological purpose such as for degradation of chitin containing waste and it might be a promising biocontrol agent for plant pathogens.

Screening for In Vitro Antifungal Activity of Soil Bacteria Against Plant Pathogens

Antifungal bacteria for biological control of plant diseases or production of novel antibiotics to plant pathogens were isolated in 1997 from various soils of Ansung, Chunan, Koyang, and Paju in Korea. Sixty-four bacterial strains pre-screened from approximately 1,400 strains were tested on V-8 juice agar against eight plant pathogenic fungi using in vitro bioassay technique for inhibition of mycelial growth. Test pathogens were Aiternaria mali, Colletotrichum gloeosporioides, C. orbiculare, Fusarium oxysporum f. sp. cucumerinum, F oxysporum f. sp. lycopersici, Magnaporthe grisea, Phytophthora capsici, and Rhizoctonia solani. A wide range of antifungal activity of bacterial strains was found against the pathogenic fungi, and strain RC-B77 showed the best antifungal activity. Correlation analysis between inhibition of each fungus and mean inhibition of all eight fungi by 64 bacterial strains revealed that C. gloeosporioides would be best appropriate for detecting bacterial strains producing antibiotics with potential as biocontrol agents for plant pathogens.

Genetic diversity and biocontrol activity of Aureobasidium pullulans isolates against postharvest rots

Aureobasidium pullulans, a cosmopolitan yeast-like fungus, colonises leaf surfaces and is a potential biocontrol agent for plant pathogens. Forty-one isolates of the fungus from the surface of several fruits and vegetables cultivated in Southern Italy were compared by molecular analysis and biocontrol activity. Characterisation of the isolates by using arbitrarily primed PCR (ap-PCR) confirmed the presence of a high genetic variability within the species. All the isolates were evaluated for their ability to control postharvest grey mold of apples, and two of them (SL250 and SL236), plus a proven antagonist (isolate L47), were able to control Penicillium digitatum on grapefruit, Botrytis cinerea, Rhizopus stolonifer and Aspergillus niger on table grape and B. cinerea and R. stolonifer on cherry tomato. Furthermore, preharvest application of isolate L47 on table grape resulted in a significant reduction of grey mold ranging from 27.1 to 49.5% compared to the untreated control. Random amplified polymorphic DNA technique (RAPD) was a useful method for the identification and evaluation of the survival rate of the applied antagonist. © 1999 Elsevier Science B.V. All rights reserved.