Effect of Trichoderma asperellum and Trichoderma virens on Allium cepa L. Growth, Damping off and Basal Rot Disease Incidence and Severity in Sri Lanka

Abstract

Trichoderma species are frequently used for the biological control of phytopathogenic fungi and they have also been reported as plant growth promoters. In the present study, the effect of two Trichoderma spp. i.e. Trichoderma asperellum and Trichoderma virens isolated from the soils of onion fields on the growth of Allium cepa L. plants and suppression of damping off and basal rot diseases was evaluated under field conditions. The two Trichoderma spp. were mass cultured in a low cost medium containing molasses and yeast and added to a low cost carrier medium consisting of talc. Two formulations, i.e. T. asperellum only and T. asperellum in combination with T. virens were prepared and the formulations were tested for their effect on onion seedlings at the nursery stage and also on transplanted plants in the field. At the nursery stage, the two formulations were applied using two methods i.e. soil application prior to planting of onion seeds or priming of onion seeds with the two formulations separately before planting. Both methods reduced the incidence and severity of damping off disease while increasing the growth of seedlings significantly (p ≤ 0.05) at the nursery stage. Additional treatment with the two formulations as seedling root dips or soil applications before transplanting the seedlings in the field were effective in controlling basal rot disease of A. cepa L. and enhancing the growth of Allium cepa L. plants significantly (p ≤ 0.05) in the field.