Chitinase and β-1,3-glucanase activities of Trichoderma harzianum in response towards pathogenic and non-pathogenic isolates: Early indications of compatibility in consortium

Potential of yeasts as biocontrol agents against Fusarium graminearum in vitro and on corn

AIMS

The antifungal effect of the yeast species Kluyveromyces marxianus, Meyerozyma caribbica, and Wickerhamomyces anomalus was evaluated against two Fusarium graminearum strains (FRS 26 and FSP 27) in vitro and on corn seeds.

METHODS AND RESULTS

The antifungal effect of the yeasts against F. graminearum was evaluated using scanning electron microscopy and extracellular chitinase and glucanase production to further elucidate the biocontrol mode of action. In addition, the germination percentage and vigor test were investigated after applying yeast on corn seeds. All the yeast strains inhibited fungal growth in vitro (57.4%-100.0%) and on corn seeds (18.9%-87.2%). In co-culture with antagonistic yeasts, F. graminearum showed collapsed hyphae and turgidity loss, which could be related to the ability of yeasts to produce chitinases and glucanases. The three yeasts did not affect the seed corn germination, and W. anomalus and M. caribbica increased corn seed growth parameters (germination percentage, shoot and root length, and shoot dry weight).

CONCLUSION

Meyerozyma caribbica and W. anomalus showed satisfactory F. graminearum growth inhibition rates and did not affect seed growth parameters. Further studies are required to evaluate the application of these yeasts to the crop in the field.

Ilex paraguariensis Hosts Root-Trichoderma spp. with Plant-Growth-Promoting Traits: Characterization as Biological Control Agents and Biofertilizers

In this study, the effect of native plant-growth-promoting microorganisms (PGPM) as bio-inoculants was assessed as an alternative to improve Ilex paraguariensis Saint Hilaire growth in the nursery. Fourteen Trichoderma strains isolated from yerba mate roots were evaluated in vitro for their potential as biological control agents (BCA) and PGPM. The PGPM properties were evaluated through the strain's antagonistic activity against three fungal pathogens (Alternaria sp., F. oxysporum, and F. solani) plus the production of extracellular cell-wall-degrading enzymes such as chitinase, β-1,3-glucanase, and cellulase. These results were used to calculate different PGPM indices to select the strains with the optimal properties. Four Trichoderma strains: T. asperelloides LBM193, LBM204, LBM206, and Trichoderma sp. LBM202, were selected based on their indirect and direct PGPM properties used in an inoculation assay on yerba mate plants in greenhouse conditions. A highly significant positive effect of bio-inoculation with these Trichoderma strains was observed in one-year-old yerba mate seedlings. Inoculated plants exhibited a greater height, chlorophyll content, and dry weight than un-inoculated plants; those treated with LBM193 manifested the best results. Yerba mate plants treated with LBM202 exhibited a healthy appearance and were more vigorous, showing potential for biocontrol agent. In conclusion, yerba mate seedlings in the Misiones region were found to have a reservoir of Trichoderma species that increases the yield of this crop in the nursery and protects them from adverse biotic and abiotic agents.

Biosafe Management of Botrytis Grey Mold of Strawberry Fruit by Novel Bioagents

Recently, there have been urgent economic and scientific demands to decrease the use of chemical fungicides during the treatment of phytopathogens, due to their human health and environmental impacts. This study explored the biocontrol efficacy of novel and eco-friendly preen (uropygial) oil and endophytic Bacillus safensis in managing postharvest Botrytis grey mold in strawberry fruit. The preen oil (25 μL/mL) showed high antifungal activity against B. cinerea Str5 in terms of the reduction in the fungal radial growth (41.3%) and the fungal colony-forming units (28.6%) compared to the control. A new strain of Bacillus safensis B3 had a good potential to produce chitinase enzymes (3.69 ± 0.31 U/mL), hydrolytic lipase (10.65 ± 0.51 U/mL), and protease enzymes (13.28 ± 0.65 U/mL), which are responsible for the hydrolysis of the B. cinerea Str5 cell wall and, consequently, restrict fungal growth. The in vivo experiment on strawberry fruit showed that preen (uropygial) oil reduced the disease severity by 87.25%, while the endophytic bacteria B. safensis B3 reduced it by 86.52%. This study reports the efficiency of individually applied bioagents in the control of phytopathogenic fungi for the first time and, consequently, encourages their application as a new and innovative strategy for prospective agricultural technology and food safety.

Development of next-generation formulation against Fusarium oxysporum and unraveling bioactive antifungal metabolites of biocontrol agents

Biocontrol agents serve as a sustainable means of controlling wilt caused by the widespread plant pathogen, Fusarium oxysporum f. sp. lycopersici. The present study aimed to develop water dispersible granules (WDG) using response surface methodology (RSM) for Bacillus subtilis MTCC 2274 and Trichoderma harzianum MTCC 3928, and to compare their antifungal efficacy with other formulations. Further, characterization of the bioactive metabolites responsible for biocontrol was performed. A new microbial formulation, WDG, was developed in the present study with talcum powder (substrate), alginic acid (dispersing agent) and acacia gum (wetting agent) (suspensibility 82.23%; wetting time 2.5 min; dispersion time 10.08 min) that fulfilled the guidelines of Collaborative International Pesticides Analytical Council (CIPAC). In planta study demonstrated that WDG of B. subtilis showed maximum reduction in disease incidence (48%) followed by talc formulation of B. subtilis (44%) and WDG of T. harzianum (42%) with profound effect on plant growth promotion. B. subtilis and T. harzianum demonstrated protease (929 and 846 U ml⁻¹ min⁻¹), chitinase (33.69 and 154 U ml⁻¹ min⁻¹), and β-1,3-glucanase (12.69 and 21.47 U ml⁻¹ min⁻¹) activities. Culture filtrates of B. subtilis and T. harzianum exhibited significant inhibition against mycelial growth of pathogen. The compounds present in the culture filtrates were identified with GC–MS as fatty acids, alkanes, phenols, benzene, pyran derivatives etc. The major non-volatile compounds in bioactive antifungal fraction were identified as derivatives of morpholine and piperdine for T. harzianum and B. subtilis, respectively. The findings propose a multivariate biocontrol mechanism against phytopathogen by production of hydrolytic enzymes, volatile and non-volatile compounds, together with development of an efficient next-generation formulation.

Encapsulation of Trichoderma harzianum Preserves Enzymatic Activity and Enhances the Potential for Biological Control

Trichoderma harzianum is a biological control agent used against phytopathogens and biostimulation in agriculture. However, its efficacy can be affected by biotic and abiotic factors, and microencapsulation has been used to maximize the efficacy. The objective was to develop polymeric microparticles to encapsulate T. harzianum, to perform physicochemical characterization to evaluate its stability, to evaluate effects on the soil microbiota, antifungal activity in vitro and enzymatic activity. Size distribution of wet and dry microparticles was 2000 and 800 μm, respectively. Scanning electron microscopy showed spherical morphology and encapsulation of T. harzianum. Photostability assays showed that encapsulation protected the fungus against ultraviolet radiation. The evaluation of the microbiota showed that the proportion of denitrifying bacteria increased when compared to the control. The T. harzianum encapsulation showed an improvement in the chitinolytic and cellulosic activity. In vitro tests showed that encapsulated fungus were able to provide a greater control of S. sclerotiorum.

Production of chitosan-oligosaccharides by the chitin-hydrolytic system of Trichoderma harzianum and their antimicrobial and anticancer effects

Chitosan-oligosaccharides (COS) are low-molecular weight chitosan derivatives with interesting clinical applications. The optimization of both COS production and purification is an important step in the design of an efficient production system and for the exploration of new COS applications. Trichoderma harzianum is an innocuous biocontrol agent that represents a novel biotechnological tool due to the production of extracellular enzymes, including those that produce a COS mixture. In this work, we propose different systems for the production of COS using the T. harzianum chitinolitic system. A complete qualitative and quantitative analysis of a partially purified COS mixture were performed. Also, an evaluation of the anticancer and antimicrobial effects of the COS mixture was carried out. Three chitosan variants (colloidal, solid and solution) and two fungus stages (spores and mycelia) were tested for COS production. The best system consisted of the interaction of the solid chitosan and the fungal spores, producing a COS mixture containing species from the monomer to the hexamer, in a concentration range of 7-238 mg/mL, according to chromatographic analysis. The proposed purification method isolated the monomer and the dimer from the COS mixture. Moreover, the COS mixture has an inhibitory effect on the growth of bacteria and changes the morphology of yeasts. As anticancer compounds, COS inhibited the growth of cervical cancer cells at concentration of 4 mg/mL and significantly reduced the survival rate of the cells. In conclusion, T. harzianum proved to be an efficient system for COS mixture production.

Applications of Fungal Strains with Keratin-Degrading and Plant Growth Promoting Characteristics

Protein hydrolysates (PHs) are organic non-microbial biostimulants having beneficial effects on plants. The study was designed to assess the effects on plants by the applications of PHs obtained from Trichoderma isolates grown on keratin wastes. Trichoderma isolates were characterized for indole-3-acetic acid and siderophores production, activity of lytic enzymes, phosphorous solubilization and inhibition of pathogens growth, using qualitative specific tests. Fungal isolates were cultured on a medium with keratin wastes (wool and feathers) to obtain PHs. Fungal PHs were tested in vivo for plant biostimulant action, as follows: (i) seeds germination test; (ii) activation of plant proton pump; (iii) evaluation of effect on tomato seedling growth. PHs from T. asperellum cultured on feathers medium reached the highest values for all parameters recorded (plant height and diameter, number of leaves and branches), with the exception of those for plant biomass, which were maximum for the wool medium. The metabolites released by keratin degradation under the activity of selected T. asperellum isolate improved crop health and productivity. The use of PHs can be a reasonable solution for the environmental pollution of by-products from the food chain, as well as for the replacement of chemical fertilizers with microbial formulations to stimulate plant growth.

Vinegar residue compost as a growth substrate enhances cucumber resistance against the Fusarium wilt pathogen Fusarium oxysporum by regulating physiological and biochemical responses

Fusarium wilt caused by the fungus Fusarium oxysporum f. sp. cucumerinum (FOC) is the most severe soil-borne disease attacking cucumber. To assess the positive effects of vinegar residue substrate (VRS) on the growth and incidence of Fusarium wilt on cucumber, we determined the cucumber growth parameters, disease severity, defense-related enzyme and pathogenesis-related (PR) protein activities, and stress-related gene expression levels. In in vitro and pot experiments, we demonstrated the following results: (i) the VRS extract exhibited a higher biocontrol activity than that of peat against FOC, and significantly improved the growth inhibition of FOC, with values of 48.3 %; (ii) in response to a FOC challenge, antioxidant enzymes and the key enzymes of phenylpropanoid metabolic activities, as well as the PR protein activities in the roots of cucumber, were significantly increased. Moreover, the activities of these proteins were higher in VRS than in peat; (iii) the expression levels of stress-related genes (including glu, pal, and ethylene receptor) elicited responses to the pathogens inoculated in cucumber leaves; and (iv) the FOC treatment significantly inhibited the growth of cucumber seedlings. Moreover, all of the growth indices of plants grown in VRS were significantly higher than those grown in peat. These results offer a new strategy to control cucumber Fusarium wilt, by upregulating the activity levels of defense-related enzymes and PR proteins and adjusting gene expression levels. They also provide a theoretical basis for VRS applications.

Biochemical Characterization of a Novel Acidic Exochitinase from Rhizomucor miehei with Antifungal Activity

A novel chitinase gene (RmChi44) from Rhizomucor miehei was cloned and expressed in Escherichia coli as an intracellular soluble and active protein. The recombinant chitinase (RmChi44) was purified to homogeneity and biochemically characterized. The molecular mass of RmChi44 was estimated to be 44.6 kDa on SDS-PAGE. RmChi44 displayed an acidic pH optimum of 4.5 and was stable within pH 4.5-9.0. The optimal temperature of RmChi44 was found to be 50 °C. The Km values of RmChi44 for colloidal chitin and glycol chitin were 4.02 and 1.55 mg/mL, respectively. RmChi44 hydrolyzed colloidal chitin to yield mainly N-acetyl chitobiose, exhibiting an exotype cleavage pattern. Moreover, the enzyme displayed β-N-acetylglucosaminidase activity, splitting N-acetyl COSs with degree of polymerization (DP) 2-5 into their monomer. In addition, RmChi44 showed antifungal activity against some phytopathogenic fungi. This is the first report on an exochitinase showing β-N-acetylglucosaminidase activity and antifungal activity from Rhizomucor species.