Management of the soil-borne fungal pathogen – Verticillium dahliae Kleb. causing vascular wilt diseases

Vascular wilt diseases caused by Verticillium dahliae Kleb. are difficult to control and lead to increasing losses of many crops worldwide. It can cause disease on not only horticultural crops but also many economically important crops such vegetables, legumes, forest trees, woody and herbaceous plants. Reasons of this situation are various: (i) the specialization of crop production resulted in the accumulation of the pathogen in the soil, especially monoculture production; (ii) the lack of an efficient and safe soil fumigation method; (iii) the production in large amounts of survival structures—microslerotia and melanized hyphae that are resistant to chemical and biological degradation.Due to the lack of effective synthetic agents for eradication of V. dahliae from soil, considerable interest in this paper has been focused on biological control, especially the selection of microorganisms with mycoparasitic activity towards V. dahliae microsclerotia, that can decrease their number in soil. The main attention is paid on the Trichoderma fungi, non pathogenic Fusarium spp., Talaromyces flavus and bacteria Bacillus spp., Pseudomonas spp. and Streptomyces spp. that are discussed in this review. In this work the suppressive effect of organic amendments against this soil-borne pathogen is also mentioned. In addition biofumigation using toxic plant materials, which is an approach to the soil-borne pathogen management could be an effective method to control diseases caused by V. dahliae.

Microbes as Bioindicators for Contamination of Shatt Al-Arab Sediments in Basrah, Iraq

Shatt Al-Arab River in Basrah, Iraq represents an important source of fresh water so the current study aimed to determine the extent of pollution of the Shatt al-Arab River with some heavy metals and hydrocarbons by measuring their concentrations in sediment samples collected from different stations along the river, as well as the adoption of biomarkers represented by bacteria and fungi in determining the extents of such pollution. The results indicate that the river is contaminated with the following metals: : Ni, Cr, Zn, Pb, Cu and Cd. The total mean concentrations of heavy metals in the exchangeable part were high with 55.23, 53.76, 40.52, 33.84, 32.70 and 14.88 µg/g, respectively. The results also indicated a high concentration of hydrocarbons where the total mean was 28.52 µg/g. Bacteria and fungi represent vital indicators of heavy metals and hydrocarbons pollution in the environment. Different types of bacteria (Sphingomonas paucimobilis, Bacillus subtilis, Pseudomonas aeruginosa, Streptococcus thoraltensis, Staphylococcus lentus, Leuconostoc cremoris and Leuconostoc mesenteroides) and fungi (Aspergillus terreus, Aspergillus fumigatus, Aspergillus niger, Curvularia sp., Eurotium cristatus, Talaromyces flavus, Mucor sp., Rhizopus sp., Trichoderma sp., Dichotomomyces cejpii, and Penicillium spp.) have been isolated from the same sediment. Isolated of specific genera from bacteria and fungi like these isolated in the present study from the sediment of all studied stations reinforce the rest of the results recorded during the current study and confirms the pollution of the river with the studied pollutants.

Bacteria and Mold Spore Heat Resistance in Guava Juice and Its Control by pH and Sodium Benzoate

Heat-resistant bacteria and molds can survive the pasteurization conditions used in high-acid fruit juices. The objective of this study was to evaluate the log reductions and thermal inactivation kinetics of spores of Bacillus subtilis bacteria and ascospores of Talaromyces flavus and Eupenicillium javanicum molds under influence of pH and sodium benzoate preservative. The spores were suspended in guava juice, processed at 90-100°C for B. subtilis and at 80-90°C for T. flavus and E. javanicum, and decimal reduction ( D ) values were estimated from the log survivor curves. Next, the effects of pH change (3.5-4.5) and 0.015% sodium benzoate addition on the D values of spores were investigated. Lower D values were obtained at higher temperatures ( D 100 ° C value of 2.32 min vs. D 90 ° C value of 15.33 min for B. subtilis, D 90 ° C value of 2.96 min vs. D 80 ° C value of 59.52 min for T. flavus, and D 90 ° C value of 1.58 min vs. D 80 ° C value of 21.32 min for E. javanicum). The D values decreased further (to 1.8 min at 100°C for B. subtilis, to 2.33 min at 90°C for T. flavus, and to 1.49 min at 90°C for E. javanicum) when the pH of guava juice was decreased from 4.1 to 3.5. Inclusion of sodium benzoate in pH 3.5 juice enhanced the thermal inactivation of spores ( D 100 ° C value decreased to 1.4 min for B. subtilis, to 1.98 min for T. flavus, and to 1.34 min for E. javanicum). To conclude, the combination of low pH and sodium benzoate provided the best method for spore inactivation, which could enhance food safety and extend food’s shelf life.

Verticillium klebahnii and V. isaacii Isolates Exhibit Host-dependent Biological Control of Verticillium Wilt Caused by V. dahliae

Verticillium dahliae, the soil-borne fungal pathogen, causes vascular wilt on many economically important crops resulting in significant yield losses. Verticillium klebahnii (isolate PD659) and V. isaacii (isolate PD660), two related species that cause little or no symptoms in some hosts, were evaluated as potential biocontrol agents (BCA) in eggplant, lettuce, and tomato by pre, post, and co-inoculation with a virulent race 1 isolate of V. dahliae (VdLs16). Initial studies demonstrated that the biocontrol efficacy of both BCAs was similar to reference BCA Talaromyces flavus (NRRL15936) across all hosts (α= 0.05). Subsequent experiments with PD659 against V. dahliae isolate Sm113 from eggplant, VdLs16 and VdLs17 isolates from lettuce, and Le1811 isolate from tomato demonstrated a significant biocontrol efficacy in eggplant and tomato but not in lettuce (at 95% CI), suggesting host-dependent effectiveness of V. klebahnii. Confocal microscopy using GFP-tagged tomato V. dahliae isolate Le1811 indicated delayed xylem colonization or lack of pathogen progression into the vascular system in a host-dependent manner on BCAs treated plants. Quantitative analyses of the expression of defense-related genes PR1a, PR5, acidic extracellular b-1,3-glucanase (GlucA), basic intracellular b-1,3-glucanase (GlucB), acidic extracellular chitinase (Chi3), basic intracellular chitinase (Chi9), and cysteine proteases (cysProreases) in tomato in the presence or absence of PD659 suggested an elevated expression of defense-related genes in compatible interaction of V. dahliae-tomato cv. Early Pak. Verticillium klebahnii (PD659) may delay the entry of V. dahliae by competing for space or nutrients during the initial stages of root colonization.

Effectiveness of isolated compound from Aloe barbadensis Miller and its formulated ointment against bacteria and fungi

Ethnomedicinally, the family Liliaceae is prominent in controlling skin, wound and fungal infections. A carboxylic fatty acid derivative has been isolated from Aloe vera leaves and its structure was elucidated on the basis of NMR and FT-IR analysis. The compound was formulated as ointment with the aid of polymer based delivery agent. The ointment and the uncontaminated fatty acid have been scrutinized aimed at their anti-infectious potential. Individually, the pure compound and the formulated ointment exhibited growth inhibitory activity against Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, Candida albicans and Talaromyces flavus. Minimum inhibitory concentration (MIC) values were found to be appreciably low, ranging between 0.30 and 2.50 mg/ml. The formulated ointment displayed highly significant inhibitory activities against all six pathogens compared to the unformulated compound. The MIC values of the ointment ranged between 0.08 and 1.25 mg/g. The in vitro antibiotic activity studies discovered that, both the pure compound and the formulated ointment showed potency against the selected multi-resistant microorganisms tested in the current work. These findings suggest that the isolated carboxylic acid derivative may be beneficial in the discovery of antibiotics highly potent against drug-resistant pathogens. Furthermore, it may add to the improvement of preservatives in the food industry. Lastly, it could be considered as new source of natural antibiotics in the pharmaceutical industry.

Diversity of soil culturable fungi in the tropical montane cloud forest of Veracruz, Mexico

Background: Cloud forest is one of the most threatened ecosystems in the world and more than half of its original area has been transformed for other land uses. Consequently, macro- and microorganisms of this ecosystem have likely undergone changes. Objective: To analyze the diversity of saprobic filamentous soil cultured fungi in four cloud forest fragments and evaluate the similarity in species composition among fragments. Methods: To detect and isolate soil microfungi, the soil particle filtration technique was used. Emerging colonies were transferred to a culture medium for subsequent quantification and identification. For each species, permanent and semi-permanent slide preparations were made, and taxonomic identification was performed based on morphological features. Results and conclusions: From 20 soil samples and 2000 inoculated particles, 233 species were distinguished. The most common species were Myrmecridium schulzeri, Pestalotiopsis maculans, Trichoderma atroviride, Virgaria nigra, Trichoderma cremeum, Fusarium solani, Cordana terrestris, Aspergillus fischeri, and Penicillium olsoni. The most abundant species were Talaromyces flavus and Pestalotiopsis maculans. All the forest fragments had a high richness, diversity, and evenness in addition to a high turnover and high number of exclusive species.