Biocontrol Effects of Trichoderma Species on Alternaria alternata keissl. , The Causal Agent of Tomato Target Spot Under In Vitro conditions

Alternaria target spot is one of the important diseases of tomato (Solanum lycopersicum) leading to substantial yield loses worldwide. The genus Trichoderma comprises a great number of fungal isolates that act as biological control agents, the antagonistic properties of which are based on the activation of multiple mechanisms. Trichoderma strains exert biocontrol against fungal phytopathogens either indirectly, by competing for nutrients and space, modifying the environmental conditions, promoting plant growth and plant defensive mechanisms, antibiosis, or directly, by mechanisms such as mycoparasitism.MATERIALS AND METHODS: The fungus pathogen, Alternaria alternata keissl. was isolated from transitional part between healthy tissue and brown spots on tomato leaves. The fungus was maintained on Potato Dextrose Agar (PDA) at 25 ᵒC. In this study biocontrol activities of 4 species of Trichoderma against A. alternata has been evaluated. A dual culture test on the potato dextrose agar was conducted in vitro to assay the ability of biocontrol agents viz, T. koningii T. brevicompactum T. harzianum T. virens to inhibit growth of Alternaria pathogen. All treatments were carried out in triplicate. They were incubated at 25 ᵒC and the diameter of the colonies was measured after 10 days. The biocontrol activity was assesed as the percentage of mycelial growth inhibition according to Edington et al., ( 1971). as fallows :Percentage of mycelial growth inhibition = [(dc-dt)/dc × 100]. where dc = average diameter of fungal colony in control and dt denotes the average diameter of fungal colony in treatment.All of four species of Trichoderma inhibited the growth of the fungus pathogen. among them T. koningii and T. brevicompactum had more inhibition effect on Alternaria. In dual culture test T. koningii caused maximum inhibition of radial growth of Alternaria (77%) followed by T. brevicompactum (73%). The strong reducing effect of these species towards Alternaria can be applied in biological control of this pathogen

کلیدواژه ها:

Alternaria ، Biocontrol ، Trichoderma ، Tomato