Biological control of early blight of tomato with epiphytic strains of Trichoderma

Early blight incited by Alternaria spp. is one of the destructive diseases of tomato which causes considerable crop yield losses. Biological control of the disease with epiphytic fungi as phyllosphere competent microorganisms is a suitable alternative to chemical pesticides. In order to isolating the fungi, healthy tomato plants were collected and small pieces of leaves and stems were placed in distilled water on a shaker and the aliquot was cultured. In search for biocontrol strains, isolated fungi were screened against the fungal pathogen (Alternaria alternata SN1–1) using dual culture as well as the volatile and non–volatile metabolites tests in vitro andeffective isolates were selected to study their efficacy on disease control under greenhouse conditions. Conidial suspension of epiphytic fungi was sprayed two times on the aerial parts of the plant in greenhouse. Two weeks after inoculation of the pathogen, the disease severity was evaluated based on a 0–9 scale. Results of screening test showed that epiphytic fungi inhibited the mycelial growth of the pathogen in various degrees. Maximum inhibition in dual culture, volatile and non–volatile metabolites tests were 70%, 53% and 68%, respectively. In greenhouse, the least disease indexes were recorded for the isolates F1–22 and P4––1 (81.4% disease control) together with P1–1 and P2–1 (74.4% disease control). Isolates F1–22, P4–1 and P2–1 identified as Trichoderma harzianum and isolate P1–1 identified as Trichoderma longibrachiatum.