Investigation on the Effect of Different Levels of Temperature and pH of some Trichoderma Isolates for Biological Control of Tomato Wilt Disease under Laboratory and Greenhouse Conditions

Document Type : Research Article


1 Gorgan University of Agricultural Sciences and Natural Resources

2 Gorgan University of Agricultural Sciences and Natural Resources.


Introduction: Vascular wilt caused by Fusarium oxysporum is one of the most important problems in producing tomtao. Recently, using the method of biological control by beneficial microorganisms of plant pathogens has an important role in crop management programs. A number of Trichoderma species are now available commercially to be used (discretely or in combination with reduced amount of chemical pesticides) for plant pathogens control. These biocontrol agents include strains belonging to the fungal genera such as Trichoderma and Gliocladium, which these species are the most intensively studied species. They are the most isolated soil-borne fungi commonly found in plant root ecosystem and these opportunistic, a virulent plant symbionts are also antagonistic towards many phytopathogenic fungi. Depending upon the strain, the application of Trichoderma has been proven to improve root and plant growth and induce resistance in plants, as well. In order to utilize the full potential of Trichoderma species in specific applications, precise identification and characterization of these fungi is vital. Trichoderma species are saprophytic fungi with minimal nutritional needs, which secrete a wide range of secondary metabolites conferring major ecological benefits to their host plants.
Materials and Methods: In this study, the fungal isolates were cultured using dual culture to assess the nutritional competitiveness, colonization and mean percentage of growth inhibition between Trichoderma isolates and Fusarium oxysporum in three temperature levels (20, 25 and 300C) and pH (4, 5 and 6.5) in PDA. If one colony has a faster growth rate than the other, a curve in the contact zone would most probably be observed. Then, the effect of growth indices were measured in both methods of cell suspensions injection and mixing the biocontrol agent (Trichoderma species) into the soil in comparison with control in greenhouse condition .In order to evaluate the effect of temperature and pH on the antagonistic activity of native Trichoderma species from kitchen garden crops on the pathogen and greenhouse studies, a factorial experiment was designed in a randomized complete block in vitro and greenhouse.
Results and Discussion: The results showed that the biocontrol characteristic of antagonistic species depended on the type of Trichoderma isolate, temperature conditions and pH. This study indicated that all five native species isolates can reduce mycelia growth of F. oxysporum in dual culture in vitro. As for the ability of Trichoderma species in growth inhibition, there was significantly different in the level of %1 for temperature and pH treatments. T. harzianum (Ah90) had the highest antagonistic activity with 58.33% inhibition of growth at 300C in pH 6.5. On the other hand, environmental parameters such as temperature and pH were effective on germination and growth of the germ tube in antagonistic species and mycelia growth. As to the contact of Trichoderma isolates and the pathogenic agent, the growth of mycelia was very low and the amount of spore in the pathogen was reduced compared with the control. After 35 days, there were significant differences in the growth indices (average fresh and dry weight and plant height) in both injection of suspension and mixing the biocontrol agent by soil with control in greenhouse condition. Using antagonists in greenhouse conditions caused an increase in plant growth system due to earlier deployment and better absorption of water and nutrients by the plant. According to the statistical analysis, antagonistic activity of T. harzianum (Ah90) plus pathogen were greater than the other two species compared with infected control and increased total dry weight by 2.14 g and plants height by 2.32 cm. Adding Trichoderma to soil prior to cultivation had a greater effect on disease control than suspension injection in the soil as the antagonist spores in suspension were not available to the root in long term and removed from the root. While in soil application, soil immersion significantly decreased tomato wilt compared to control treatment.
Conclusion: In a temperature range of 33 oC, soil pH of 5.6 and by application of soil inoculation, T. harzianum (Ah90) isolated from cucurbit fields in Khorasan province was found to be the most suitable species leading to reduced disease and increasing the vegetative parts of the plant under greenhouse conditions.


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