Biological Effects of Trichoderma spp. Isolated from Tomato Rhizosphere and Trichomax-HV Biofungicide against Tomato Fusarium Wilt in Vitro

Fusarium wilt of tomato is one of the most important and common tomato diseases growing in the cultivated areas of this plant around the world. Biological control of plant diseases using non-pathogenic microorganisms has attracted the attention of many researchers. Trichoderma is one of the most successful and widely used microorganisms that prevent fungal damage in plants. Trichoderma spp. have different mechanisms to deal with plant pathogens, such as increasing plant resistance and activating defense reactions, direct confrontation with the pathogen through mycoparasitism, antibiosis, competition, plant growth stimulation, regulation and induction of plant growth factors including auxins, cytokinins and ethylene that stimulate growth Plants are involved. Totally, they destroyed biological reproductive organs, survival and reproduction, weakening and expelling pathogens from plant debris and preventing the formation of contaminants are the three basic methods by which biological control is achieved. Trichoderma is one of the living fungi that can perform the above three mechanisms simultaneously and as a result it is used as a biological fungus that increases plant growth and activity of beneficial microorganisms.

In this study, the effects of two isolates; Trichoderma harzianum and Trichoderma virens, and biological toxin of Trichomax-HV against Fusarium oxysporum f. sp. lycopersici which is the agent of Fusarium wilt disease in tomato was evaluated in the laboratory and greenhouse. Trichomax-HV is a biofungicide that use as commercially. During summer and autumn, tomato plants with obvious signs of Fusarium wilt were collected from tomato fields in different parts of Lorestan province and transferred to the laboratory. Isolation of pathogenic fungi was performed according to Bani Hashemi and Dezeeuw methods using acidic PDA culture medium. Antagonistic activity of these isolates against this pathogen was studied by dual culture method in the laboratory. In order to investigate the effect of these antagonist isolates in the greenhouse, first the inoculum of pathogenic fungus and fungal antagonists were added to the pots as soon as the seedlings were transferred to the pots and then after 60-days, the interactions between the pathogen and antagonist was evaluated. This test was performed in a completely randomized design with 10 treatments and three replications. The data obtained from the experiment were statistically analyzed using SPSS 16 software and the average of the treatments were compared using Duncan's multiple range test at 5% probability level.

In this study, a total of three isolates of F. oxysporum f. sp. lycopersici were isolated from tomato plants infected with Fusarium wilt disease from Robat and Chegeni Dore tomato fields (Khorramabad city) and Cham fig fields (Poldokhtar city) that was assigned them codes FOM, FOK and FOS respectively. A total of 27 fungal isolates were isolated from soil samples of tomato rhizosphere collected from tomato fields of two cities in Lorestan province. By evaluating the inhibitory effect of these isolates on pathogenic growth, two isolates prevented the growth of pathogenic mycelium by creating an inhibitory aura. The results of laboratory studies showed that T. harzianum by 48.9 percent, Trichomax-HV by 45.6 percent and‏ T. virens to 22.36 percent prevented the growth of pathogen and colonized the pathogen’s colonies (in comparison with the control). Antagonist agents in greenhouse experiments increased stem height, wet and dry weight of shoots and root in the absence of pathogen. Comparing with the control sample, only the isolate T. harzianum in the interaction with the pathogen increased the plant height, wet and dry weight of shoots and root. According to study, in the greenhouse biological tests of biofungicide (Trichomax-HV) and Trichoderma spp. had shown good control on causal agent of the disease (Fusarium oxysporum f. sp. lycopersici). Among these treatments, T. harzianum had the best effect on the control of pathogenic fungi, which is due to the complex system of soil biology and ecology and the presence of antagonists in the rhizosphere and the power of root colonization and antagonist survival, soil pH and soil texture.

Based on the this study results, T. harzianum had the highest percentage of inhibition of pathogenic fungal growth as well as increase in height, fresh and dry weight of the plant and decrease in disease severity among the different treatments tested. In greenhouse conditions, T. harzianum prevented from tomato Fusarium wilt disease (caused by Fusarium oxysporum f. sp. lycopersici) in very large extent. Also this results showed that Trichomax-HV could be a viable alternative to chemical fungicides in controlling this disease.