Mycelial Growth Of Fungal Pathogens Research Articles

Pseudomonas synxantha volatile organic compounds: efficacy against Cadophora luteo-olivacea and Botrytis cinerea of kiwifruit.

Volatile organic compounds (VOCs) are responsible for the antagonistic activity exerted by different biological control agents (BCAs). In this study, VOCs produced by Pseudomonas synxantha strain 117-2b were tested against two kiwifruit fungal postharvest pathogens: Cadophora luteo-olivacea and Botrytis cinerea, through in vitro and in vivo assays. In vitro results demonstrated that P. synxantha 117-2b VOCs inhibit mycelial growth of C. luteo-olivacea and B. cinerea by 56% and 42.8% after 14 and 5 days of exposition, respectively. In vivo assay demonstrated significant inhibitory effects. VOCs used as a biofumigant treatment reduced skin-pitting symptoms disease severity by 28.5% and gray mold incidence by 66.6%, with respect to the untreated control. BCA volatiles were analyzed by solid-phase microextraction coupled with gas chromatography-mass spectrometry (SPME-GC/MS), and among the detected compounds, 1-butanol, 3-methyl and 1-nonene resulted as the most produced. Their efficacy as pure synthetic compounds was assayed against mycelial growth of fungal pathogens by different concentrations (0.34, 0.56, and 1.12 µL mL-1 headspace). The effect of the application of VOCs as a biofumigant was also investigated as the expression level of seven defense-related genes of kiwifruit at different exposition times. The results indicated an enhancement of the expression of almost all the genes starting from 3h of treatment. These results described P. synxantha VOCs characteristics and their potential as a promising method to adopt for protecting kiwifruit from postharvest diseases caused by C. luteo-olivacea and B. cinerea.

BIO-MANAGEMENT OF FUNGAL LEAF SPOT OF TOMATO (SOLANUM LYCOPERSICUM L.) USING INDIGENOUS TRICHODERMA ISOLATES

One of the main obstacles to feeding the world is the fungal leaf spot disease, which has a negative impact on plants' photosynthetic areas and significantly lowers crop quality and output. To manage fungi that pose a serious hazard to both humans and the environment, various chemical fungicides are utilized. The goal of the current study was to determine whether local isolates of three Trichoderma spp. (Trichoderma viride, Trichoderma harzianum, and Trichoderma asperellum) had any antagonistic effects in vitro against the pathogenic fungi Alternaria alternata, Fusarium solani, Fusarium oxysporum, Aspergillus flavus, Aspergillus sydowii, and Alternaria sp. Trichoderma viride showed the greatest growth inhibition against all of the tested pathogenic fungi, followed by Trichoderma harzianum and Trichoderma asperellum. It was shown that all three Trichoderma species strongly inhibited the mycelial growth of fungal pathogens. Compared to other isolated fungi, Trichoderma species inhibited Alternaria alternata mycelial growth more, whereas in Fusarium oxysporum least amount of mycelial growth inhibition was observed. These findings imply that Trichoderma species can function as an effective biocontrol agent against the fungi responsible for tomato leaf spot disease.

Volatile Organic Compound from Trichoderma asperelloides TSU1: Impact on Plant Pathogenic Fungi.

Soil microorganisms are well studied for their beneficial effects on plant growth and their impact on biocontrol agents. The production of volatile antifungal compounds emitted from soil fungi is considered to be an effective ability that can be applied in biofumigants in the control of plant diseases. A soil fungus, Trichoderma asperelloides TSU1, was isolated from flamingo flower cultivated soil and identified on the basis of the morphology and molecular analysis of the internal transcribed spacer (ITS), rpb2, and tef1-α genes. To test T. asperelloides TSU1-produced volatile organic compounds (VOCs) with antifungal activity, the sealed plate method was used. The VOCs of T. asperelloides TSU1 inhibited the mycelial growth of fungal pathogens that were recently reported as emerging diseases in Thailand, namely, Corynespora cassiicola, Fusarium incarnatum, Neopestalotiopsis clavispora, N. cubana, and Sclerotium rolfsii, with a percentage inhibition range of 38.88–68.33%. Solid-phase microextraction (SPME) was applied to trap VOCs from T. asperelloides TSU1 and tentatively identify them through gas chromatography–mass spectrometry (GC/MS). A total of 17 compounds were detected in the VOCs of T. asperelloides TSU1, and the dominant compounds were identified as fluoro(trinitro)methane (18.192% peak area) and 2-phenylethanol (9.803% peak area). Interestingly, the commercial 2-phenyethanol showed antifungal activity against fungal pathogens that were similar to the VOCs of T. asperelloides TSU1 by bioassay. On the basis of our study’s results, T. asperelloides TSU1 isolated from soil displayed antifungal abilities via the production of VOCs responsible for restricting pathogen growth.

Luteolin-induced activation of the phenylpropanoid metabolic pathway contributes to quality maintenance and disease resistance of sweet cherry

Redox imbalance and fungal infection are major causes for quality deterioration and postharvest decay of fruit. Therefore, it is crucial to activate intrinsic antioxidative capacity and disease responses for fruit quality maintenance. Although plant-derived flavonoids have been reported for health-promoting benefits, their roles in the maintenance of fruit quality remains largely unexplored. Here, we exogenously applied luteolin, a flavonoid substance, and further examined its efficacy in maintaining fruit quality and inhibiting fungal diseases in sweet cherry. The results showed that 100 or 200 mg/L luteolin maintained better organoleptic quality and decreased disease incidence during storage. Biochemical assays revealed that luteolin activated the phenylpropanoid metabolic pathway and improved antioxidative capacity, thereby elevating total anthocyanin and flavonoid contents. Notably, luteolin inhibited mycelial growth of fungal pathogens and reduced patulin yield by Penicillium expansum. Collectively, these results suggest that luteolin is a promising alternative for maintaining better fruit quality and ameliorating disease resistance.

Control of Wilt and Rot Pathogens of Tomato by Antagonistic Pink Pigmented Facultative Methylotrophic Delftia lacustris and Bacillus spp.

The studies on the biocontrol potential of pink pigmented facultative methylotrophic (PPFM) bacteria other than the genus Methylobacterium are scarce. In the present study, we report three facultative methylotrophic isolates; PPO-1, PPT-1, and PPB-1, respectively, identified as Delftia lacustris, Bacillus subtilis, and Bacillus cereus by 16S rRNA gene sequence analysis. Hemolytic activity was tested to investigate the potential pathogenicity of isolates to plants and humans, the results indicates that the isolates PPO-1, PPT-1, and PPB-1 are not pathogenic strains. Under in vitro conditions, D. lacustris PPO-1, B. subtilis PPT-1, and B. cereus PPB-1 showed direct antagonistic effect by inhibiting the mycelial growth of fungal pathogens; Fusarium oxysporum f. sp. lycopersici (2.15, 2.05, and 1.95 cm), Sclerotium rolfsii (2.14, 2.04, and 1.94 cm), Pythium ultimum (2.12, 2.02, and 1.92 cm), and Rhizoctonia solani (2.18, 2.08, and 1.98 cm) and also produced volatile inhibitory compounds. Under plant growth chamber condition methylotrophic bacterial isolates; D. lacustris PPO-1, B. subtilis PPT-1, and B. cereus PPB-1 significantly reduced the disease incidence of tomato. Under greenhouse condition, D. lacustris PPO-1, B. subtilis PPT-1, and B. cereus PPB-1 inoculated tomato plants, when challenged with F. oxysporum f. sp. lycopersici, S. rolfsii, P. ultimum, and R. solani, increased the pathogenesis related proteins (β-1,3-glucanase and chitinase) and defense enzymes (phenylalanine ammonia lyase, peroxidase, polyphenol oxidase, and catalase) on day 5 after inoculation. In the current study, we first report the facultative methylotrophy in pink pigmented D. lacustris, B. subtilis, and B. cereus and their antagonistic potential against fungal pathogens. Direct antagonistic and ISR effects of these isolates against fungal pathogens of tomato evidenced their possible use as a biocontrol agent.

Antifungal Efficacies of Plant Essential Oils and Main Constituents Against Soil-Borne Fungal Disease Agents of Bean

In this study, in vitro antifungal efficacies of essential oils (EO's) obtained from taxonomically different medicinal plants such as oregano (Origanum syriacum L), fennel (Foeniculum vulgare Mill.) and laurel (Laurus nobilis L.), naturally growing in the different regions of Hatay province, and their major constituents (carvacrol, trans-anethole and 1,8-cineole) were investigated against soil-borne fungal disease agents of bean plants such as Sclerotium rolfsii, Rhizoctonia solani and Macrophomina phaseolina. Inhibitory effects of volatile and contact phases of different concentrations of the essential oils used were determined on fungal hyphae. While contact phases of O. syriacum and F. vulgare EO's completely inhibited mycelial growth of fungal pathogens at 160 to 320 µg/ml concentrations, L. nobilis EO, however, completely inhibited mycelial growth at relatively higher concentrations (1440 to 2880 µg/ml). In comparison, volatile phases of all EO have completely inhibited mycelial growth at relatively lower concentrations (20 to 200 µg/ml). Major components of O. syriacum, and F. vulgare EO's, carvacrol and trans-anethole respectively, also completely inhibited mycelial growth at 130 to 440 µg/ml concentrations. Major component of L. nobilis EO, 1,8-cineole, was, however, able to show antifungal activity against only M. phaseolina at the highest concentration (3000 µg/ ml). Antimicrobial activities shown by EO's and their major constituents against fungal disease agents revealed their potential to be used as a new alternative control measures against fungal diseases of economically important plant.

Optimization and production of salicylic acid by rhizobacterial strain <italic>Bacillus licheniformis </italic> MML2501

The Rhizobacterial isolate Bacillus licheniformis MML2501 effectively inhibited the mycelial growth of fungal pathogens viz., Macrophomina phaseolina, Fusarium udum, Fusarium oxysporum, Bipolaris oryzae, Pyricularia oryzae, Alternaria alternata and Curvularia lunata. Bacillus licheniformis MML2501 was tolerant to heavy metals such as zinc, cobalt and selenium. B. licheniformis MML2501 was tolerant to fungicides such as propiconazole and tridemorph and showed moderate tolerance to tricyclazole and it was showed resistant to antibiotics such as ampicillin, streptomycin, bacitracin, cephalotitin, erythromycin and oxytetracycline. Bacillus licheniformis MML2501 produced salicylic acid (SA), with a maximum yield of 18 μg/ml in optimized culture conditions such as pH 7.0, temperature 30°C, casaminoacids at a concentration of 0.4 % and at 200 rpm shaken condition. SA produced by Bacillus licheniformis MML2501 was further confirmed by TLC and HPLC analyses, in which the Rf value and retention time of 0.61 and 5.24 min, respectively were matching with that of authentic SA. Therefore the present study suggests that the rhizobacterial strain Bacillus licheniformis MML2501 has merits to be a beneficial bacteria for the crop protection through systemic resistance.

A Bacterial Endophyte, Pseudomonas brassicacearum YC5480, Isolated from the Root of Artemisia sp. Producing Antifungal and Phytotoxic Compounds

An endophytic bacterial strain YC5480 producing antifungal and phytotoxic compounds simultaneously was isolated from the surface sterilized root of Artemisia sp. collected at Jinju area, Korea. The bacterial strain was identified as a species of Pseudomonas brassicacearum based on its 16S rRNA gene sequence analysis and physiological and biochemical characteristics. The seed germination and growth of monocot and dicot plants were inhibited by culture filtrate (1/10-strength Tryptic Soy Broth) of the strain. The germination rate of radish seeds in the culture filtrate differed in various culture media. Only 20% of radish seeds germinated in the culture media of 1/2 TSB for 5 days incubation. Mycelial growth of fungal pathogens, Colletotrichum gloeosporioides, Fusarium oxysporum and Phytophthora capsici was also inhibited by the culture filtrate of the strain YC5480. An antifungal compound, KS-1 with slight inhibitory activity of radish seed germination at 1,000 ppm and a seed germination inhibitory compound, KS-2 without suppression of fungal growth were produced simultaneously in TSB. The compounds KS-1 and KS-2 were identified to be 2,4-diacetylphloroglucinol (DAPG) and 2,4,6-trihydroxyacetophenone (THA), respectively.