Antimicrobial activity of sophorolipids produced by Starmerella bombicola against phytopathogens from cherry tomato.

BACKGROUND: Phytopathogenic microorganisms are the main cause of plant diseases, generating significant economic losses for the agricultural and food supply chain. Cherry tomatoes (Solanum lycopersicum var. cerasiforme) are very perishable plants and highly demanding in the use of pesticides; therefore, alternative solutions such as biosurfactants have aroused as a potent substituent. The main objective of the present study was to investigate the antimicrobial activity of sophorolipids against the phytopathogens Botrytis cinerea, Sclerotium rolfsii, Rhizoctonia solani and Pythium ultimum. RESULTS: The biosurfactant inhibited the mycelial growth in vitro with a minimum concentration of 2 mg mL-1 . The application of sophorolipids at 1, 2 and 4 mg mL-1 in detached leaves of tomato before the inoculation of the fungus B. cinerea was the best treatment, reducing leaf necrosis by up to 76.90%. The use of sophorolipids for washing tomato fruits before the inoculation of B. cinerea was able to inhibit the development of gray mold by up to 96.27%. CONCLUSION: The results for tomato leaves and fruits revealed that the biosurfactant acts more effectively when used preventively. Sophorolipids are stable molecules that show promising action for the potential replacement of pesticides in the field and the post-harvest process against the main tomato phytopathogens. © 2021 Society of Chemical Industry.

Plant growth promoting and antifungal activity in endophytic Bacillus strains from pearl millet (Pennisetum glaucum).

Bacterial endophytes are well known inhabitants of living plant system and perform important assignments in maintaining plant growth and health. Currently, limited reports are available on the endophytes of pearl millet (Pennisetum glaucum) reflecting antagonistic and plant growth promoting (PGP) attributes. Therefore, the major objectives of current investigation were to identify antagonistic strains of endophytic Bacillus from pearl millet and further illustrate their PGP capabilities. In this study, 19 endophytic Bacillus strains (EPP5, EPP21, EPP30, EPP32, EPP35, EPP42, EPP49, EPP55, EPP62, EPP65, EPP70, EPP71, EPP74, EPP78, EPP83, EPP86, EPP93, EPP100, and EPP102) displaying antagonistic activity towards Rhizoctonia solani (RS), Sclerotium rolfsii (SR), and Fusarium solani (FS) were isolated from different sections (root, leaf, stem, and root) of pearl millet. Phenotypic (shape, colony, gram staining reaction, endospore formation, and motility) and biochemical features (catalase, oxidase, citrate, gelatinase, urease, Voges Proskauer's, methyl red, indole, and nitrate reduction), along with the similarly comparison of 16S rRNA gene sequence with type strains identified eight antagonistic endophyhtes as B. amyloliquefaciens (EPP35, EPP 42, EPP62, and EPP 102), Bacillus subtilis subsp. subtilis (EPP65), and Bacillus cereus (EPP5, EPP71, and EPP74). The production of indole acetic acid and siderophores was varied among the isolated endophytes. Besides displaying enzymatic activities, these isolates varied in solubilizing capabilities of phosphate, potassium, and zinc. The presence of three antimicrobial peptide genes (ituD, bmyC, and srfA) also confirmed their antifungal nature. Further, single treatment of three promising strains (EPP5, EPP62, and EPP65) offered protection ranging from 35.68 to 45.74% under greenhouse conditions. However, microbial consortium (EPP5+ EPP62 + EPP65) provided the highest protection (71.96%) against root rot and wilt infection with significant increase in plant biomass. Overall, the current study indicated that pearl millet plant harbors various species of endophytic Bacillus that possess excellent biocontrol and growth promotion activities.

Effects of essential oils from two Lippia species on growth of phytopathogenic fungi / Efecto de los aceites esenciales de dos especies de Lippia sobre el crecimiento de hongos fitopatógenos

Chemical characterization of the essential oils of two Lippia species by GC-MS and NMR spectroscopy revealed that limonene (84.3%) and ß-caryophyllene (6.1%) were the most abundant components in Lippia turbinata while (6S,7S,10S)-trans-davanone (99.1%) predominated in Lippia integrifolia. Antifungal activity of the essential oils was determined by headspace volatile exposure assay against the fungal phytopathogenic Sclerotinia sclerotiorum, Sclerotium rolfsii and Rhizoctonia solani. The essential oil of L. turbinata showed potent antifungal activity against the panel of fungi tested while that the oil of L. integrifolia significantly inhibited the mycelial growth of S. rolfsii and R. solani.

La caracterización química de los aceites esenciales de dos especies de Lippia por cromatografía gaseosa-espectrometría de masas (CG-EM) y espectroscopia de RMN reveló que limoneno (84,3%) y ß-cariofileno (6,1%) fueron los componentes más abundantes de Lippia turbinata mientras que (6S,7S,10S)-trans-davanona (99,1%) predominó en Lippia integrifolia. La actividad antifúngica de los aceites esenciales se determinó por el ensayo de exposición a los vapores frente a los hongos fitopatógenos Sclerotinia sclerotiorum, Sclerotium rolfsii y Rhizoctonia solani. El aceite esencial de L. turbinata mostró una potente actividad antifúngica frente al panel de hongos ensayados, mientras que el aceite de L. integrifolia inhibió significativamente el crecimiento micelial de S. rolfsii y R. solani.

Antifungal activity, yield, and composition of Ocimum gratissimum essential oil.

Ocimum gratissimum L. or clove basil, belongs to the Lamiaceae family, has various desirable uses and applications. Beyond its aromatic, seasoning, and medicinal applications, this plant also has antimicrobial activity. This study was aimed at assessing the antifungal activity, yield, and composition of the essential oil (EO) of O. gratissimum. The species was cultivated in garden beds with dystrophic red latosol soil type containing high organic-matter content. The EO was obtained by hydrodistillation of dried leaves in a modified Clevenger apparatus, followed by determination of its content. Chemical characterization was carried out by gas chromatography-mass spectrometry (GC-MS). Microbial activity was assessed using the broth microdilution method, by determining the minimum inhibitory concentration (MIC), in order to compare the antimicrobial effect of EO in 10 isolates-Fusarium oxysporum f. sp tracheiphilum (CMM-0033), F. oxysporum f. sp. cubense (CMM-0813 and CMM-2819), F. oxysporum f. sp lycopersici (CMM-1104), F. solani (CMM-3828), Rhizoctonia solani (CMM-3274), and Macrophomina phaseolina (CMM-2715, CMM-3875, CMM-3615, and CMM-3650). The EO was a highly effective inhibitor of the studied phytopathogenic fungi, with MICs varying from 31.25 to 125 µg/mL. F. oxysporum f. sp lycopersici and R. solani were the most sensitive; both were inhibited at an MIC of 31.25 µg/mL. The EO content in the plant extract was 0.18%. Thirty chemical compounds were detected via GC-MS, with linalool (32.9%) being the major compound followed by 1,8-cineole (21.9%), both oxygenated monoterpenes. It can be concluded that clove basil EO is a highly effective antifungal agent, and therefore, a potential alternative for the control of plant pathogenic diseases.

Identification of mVOCs from Andean rhizobacteria and field evaluation of bacterial and mycorrhizal inoculants on growth of potato in its center of origin.

Food security (a pressing issue for all nations) faces a threat due to population growth, land availability for growing crops, a changing climate (leading to increases in both abiotic and biotic stresses), heightened consumer awareness of the risks related to the use of agrichemicals, and also the reliance on depleting fossil fuel reserves for their production. Legislative changes in Europe mean that fewer agrichemicals will be available in the future for the control of crop pests and pathogens. The need for the implementation of a more sustainable agricultural system globally, incorporating an integrated approach to disease management, has never been more urgent. To that end, the Valorizing Andean Microbial Diversity (VALORAM) project (http://valoram.ucc.ie), funded under FP7, examined the role of microbial communities in crop production and protection to improve the sustainability, food security, environmental protection, and productivity for rural Andean farmers. During this work, microbial volatile organic compounds (mVOCs) of 27 rhizobacterial isolates were identified using gas chromatography/mass spectrometry (GC/MS), and their antifungal activity against Rhizoctonia solani was determined in vitro and compared to the activity of a selection of pure volatile compounds. Five of these isolates, Pseudomonas palleroniana R43631, Bacillus sp. R47065, R47131, Paenibacillus sp. B3a R49541, and Bacillus simplex M3-4 R49538 trialled in the field in their respective countries of origin, i.e., Bolivia, Peru, and Ecuador, showed significant increase in the yield of potato. The strategy followed in the VALORAM project may offer a template for the future isolation and determination of putative biocontrol and plant growth-promoting agents, useful as part of a low-input integrated pest management system.

Isolation and characterization of genetic variability in bacteria with ß-hemolytic and antifungal activity isolated from the rhizosphere of Medicago truncatula plants.

In the present study, we analyzed the frequency of hemolytic and antifungal activities in bacterial isolates from the rhizosphere of Medicago truncatula plants. Of the 2000 bacterial colonies, 96 showed ß-hemolytic activities (frequency, 4.8 x 10(-2)). Hemolytic isolates were analyzed for their genetic diversity by using random amplification of polymorphic DNA, yielding 88 haplotypes. The similarity coefficient of Nei and Li showed a polymorphic diversity ranging from 0.3 to 1. Additionally, 8 of the hemolytic isolates showed antifungal activity toward plant pathogens, Diaporthe phaseolorum, Colletotrichum acutatum, Rhizoctonia solani, and Fusarium oxysporum. The 16S ribosomal sequencing analysis showed that antagonistic bacterial isolates corresponded to Bacillus subtilis (UM15, UM33, UM42, UM49, UM52, and UM91), Bacillus pumilus (UM24), and Bacillus licheniformis (UM88). The present results revealed a higher genetic diversity among hemolytic isolates compared to that of isolates with antifungal action.

Antifungal activity of metabolites of the endophytic fungus Trichoderma brevicompactum from garlic.

The endophytic fungus strain 0248, isolated from garlic, was identified as Trichoderma brevicompactum based on morphological characteristics and the nucleotide sequences of ITS1-5.8S- ITS2 and tef1. The bioactive compound T2 was isolated from the culture extracts of this fungus by bioactivity-guided fractionation and identified as 4ß-acetoxy-12,13- epoxy-Δ(9)-trichothecene (trichodermin) by spectral analysis and mass spectrometry. Trichodermin has a marked inhibitory activity on Rhizoctonia solani, with an EC50 of 0.25 µg mL(-1). Strong inhibition by trichodermin was also found for Botrytis cinerea, with an EC50 of 2.02 µg mL(-1). However, a relatively poor inhibitory effect was observed for trichodermin against Colletotrichum lindemuthianum (EC50 = 25.60 µg mL(-1)). Compared with the positive control Carbendazim, trichodermin showed a strong antifungal activity on the above phytopathogens. There is little known about endophytes from garlic. This paper studied in detail the identification of endophytic T. brevicompactum from garlic and the characterization of its active metabolite trichodermin.

Antifungal activity of metabolites of the endophytic fungus Trichoderma brevicompactum from garlic

The endophytic fungus strain 0248, isolated from garlic, was identified as Trichoderma brevicompactum based on morphological characteristics and the nucleotide sequences of ITS1-5.8SITS2 and tef1. The bioactive compound T2 was isolated from the culture extracts of this fungus by bioactivity-guided fractionation and identified as 4β-acetoxy-12,13-epoxy-Δ9-trichothecene (trichodermin) by spectral analysis and mass spectrometry. Trichodermin has a marked inhibitory activity on Rhizoctonia solani, with an EC50 of 0.25 µgmL-1. Strong inhibition by trichodermin was also found for Botrytis cinerea, with an EC50 of 2.02 µgmL-1. However, a relatively poor inhibitory effect was observed for trichodermin against Colletotrichum lindemuthianum (EC50 = 25.60 µgmL-1). Compared with the positive control Carbendazim, trichodermin showed a strong antifungal activity on the above phytopathogens. There is little known about endophytes from garlic. This paper studied in detail the identification of endophytic T. brevicompactum from garlic and the characterization of its active metabolite trichodermin.

Antifungal activity of metabolites of the endophytic fungus Trichoderma brevicompactum from garlic

The endophytic fungus strain 0248, isolated from garlic, was identified as Trichoderma brevicompactum based on morphological characteristics and the nucleotide sequences of ITS1-5.8SITS2 and tef1. The bioactive compound T2 was isolated from the culture extracts of this fungus by bioactivity-guided fractionation and identified as 4β-acetoxy-12,13-epoxy-Δ9-trichothecene (trichodermin) by spectral analysis and mass spectrometry. Trichodermin has a marked inhibitory activity on Rhizoctonia solani, with an EC50 of 0.25 µgmL-1. Strong inhibition by trichodermin was also found for Botrytis cinerea, with an EC50 of 2.02 µgmL-1. However, a relatively poor inhibitory effect was observed for trichodermin against Colletotrichum lindemuthianum (EC50 = 25.60 µgmL-1). Compared with the positive control Carbendazim, trichodermin showed a strong antifungal activity on the above phytopathogens. There is little known about endophytes from garlic. This paper studied in detail the identification of endophytic T. brevicompactum from garlic and the characterization of its active metabolite trichodermin.(AU)

Mycoparasitism studies of Trichoderma species against three phytopathogenic fungi: evaluation of antagonism and hydrolytic enzyme production.

Trichoderma spp. are used for biocontrol of several plant pathogens. However, their efficient interaction with the host needs to be accompanied by production of secondary metabolites and cell wall-degrading enzymes. Three parameters were evaluated after interaction between four Trichoderma species and plant-pathogenic fungi: Fusarium solani, Rhizoctonia solani and Sclerotinia sclerotiorum. Trichoderma harzianum and T. asperellum were the most effective antagonists against the pathogens. Most of the Trichoderma species produced toxic volatile metabolites, having significant effects on growth and development of the plant pathogens. When these species were grown in liquid cultures with cell walls from these plant pathogens, they produced and secreted ß-1,3-glucanase, NAGAse, chitinase, acid phosphatase, acid proteases and alginate lyase.

Pelargonium graveolens L'Her. and Artemisia arborescens L. essential oils: chemical composition, antifungal activity against Rhizoctonia solani and insecticidal activity against Rhysopertha dominica.

The chemical composition of the Pelargonium graveolens essential oil allowed the identification of 15 compounds (93.86% of the total essential oil). The major fractions were citronellol (35%) and geraniol (28.8%). The chemical composition of the Artemisia arborescens essential oil revealed twenty-one compounds representing 93.57% of the total essential oil. The main compounds were chamazulene (31.9%) and camphor (25.8%). The insecticidal effects were tested towards the insect Rhysopertha dominica. Results revealed that these two essential oils were highly effective against R. dominica at the dose of 50 µL on Petri dish of 8.5 cm of diameter. The antifungal activity was evaluated against Rhizoctonia solani and results showed that both of the essential oils were highly active at a dose of 12.5 µL/20 mL of PDA. Moreover, the inhibitory effect of P. graveolens essential oil was evidenced as stronger than that of the A. arborescens oil for all the tested doses.

Muscodor albus E-6, an endophyte of Guazuma ulmifolia making volatile antibiotics: isolation, characterization and experimental establishment in the host plant.

Muscodor albus is an endophytic fungus, represented by a number of isolates from tropical tree and vine species in several of the world's rainforests, that produces volatile organic compounds (VOCs) with antibiotic activity. A new isolate, E-6, of this organism, with unusual biochemical and biological properties, has been obtained from the branches of a mature Guazuma ulmifolia (Sterculiaceae) tree growing in a dry tropical forest in SW Ecuador. This unique organism produces many VOCs not previously observed in other M. albus isolates, including butanoic acid, 2-methyl-; butanoic acid, 3-methyl-; 2-butenal, 2-methyl-; butanoic acid, 3-methylbutyl ester; 3-buten-1-ol, 3-methyl; guaiol; 1-octene, 3-ethyl-; formamide, N-(1-methylpropyl); and certain azulene and naphthalene derivatives. Some compounds usually seen in other M. albus isolates also appeared in the VOCs of isolate E-6, including caryophyllene; phenylethyl alcohol; acetic acid, 2-phenylethyl ester; bulnesene; and various propanoic acid, 2-methyl- derivatives. The biological activity of the VOCs of E-6 appears different from the original isolate of this fungus, CZ-620, since a Gram-positive bacterium was killed, and Sclerotinia sclerotiorum and Rhizoctonia solani were not. Scanning electron micrographs of the mycelium of isolate E-6 showed substantial intertwining of the hyphal strands. These strands seemed to be held together by an extracellular matrix accounting for the strong mat-like nature of the mycelium, which easily lifts off the agar surface upon transfer, unlike any other isolate of this fungus. The ITS-5.8S rDNA partial sequence data showed 99 % similarity to the original M. albus strain CZ-620. For the first time, successful establishment of M. albus into its natural host, followed by recovery of the fungus, was accomplished in seedlings of G. ulmifolia. Overall, isolates of M. albus, including E-6, have chemical, biological and structural characteristics that make them potentially useful in medicine, agricultural and industrial applications.

Synthesis of a Trichoderma chitinase which affects the Sclerotium rolfsii and Rhizoctonia solani cell walls.

A Trichoderma sp. isolate, hereafter called T6, produces a 46-kDa endochitinase (CHIT 46) which had been shown to drastically affect in vitro the cell walls of the phytopathogens Sclerotium rolfsii and Rhizoctonia solani. We attempted to gain insight into its properties. The CHIT 46 N-terminal amino acid sequence shares a very high homology with other fungal chitinases. Western blot analysis using polyclonal antibodies anti-CHIT 46 revealed that this enzyme is immunologically distinct from other proteins produced by the same Trichoderma isolate T6, but is immunologically identical with proteins having equivalent molar mass, probably chitinases, produced by other Trichoderma spp. isolates. In addition, the antibodies revealed also that a substantial amount of this enzyme is secreted into the culture medium 2 d after the Trichoderma isolate T6 comes into contact with chitin.