In Vitro and In Vivo Test of Antagonistic Trichoderma Isolates Against the Causative Agent of Tomato Wilt Disease (Fusarium Oxysporum F. Sp. Lycopersici), in the Central Rift Valley of Ethiopia
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Date
2012-11-11
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Addis Ababa University
Abstract
The study was initiated with the objectives of controlling tomato wilt diseases caused by Fusarium oxysporum species and using Trichoderma species as a biocontrol agent against the test pathogen. Fusarium oxysporum the causative agent of tomato wilt disease was isolated from diseased tomato plants grown in five selected kebeles of Dugda Bora and Adami Tulu Jido-Kombolcha woredas of the Central Rift Valle (CRV) region of Ethiopia. Three Trichoderma species were isolated from the rhizosphere soil of healthy tomato plants. Trichoderma isolates were grown in different culture media namely; PDA, MEA and CDA to determine their mycelial growth. The pathogencity of isolate was determined on three different tomato varieties namely Cochoro, Miya and Fetane were grown in 20 cm plastic pots containing 3 kg of autoclaved soil in the greenhouse. The antagonistic effect of Trichoderma isolates against the test pathogen was tested both in vitro and under greenhouse conditions. Fusarium oxysporum isolate produced three types of spores on PDA medium namely microconidia, macroconidia and chlamydospores. The antagonistic effect of Trichoderma isolates against the test pathogen was tested by infesting 20 ml of Fusarium oxysporum isolate spores at a concentration of 1.5 x106 conidia/ml and 20 ml Trichoderma isolate spores with the same concentration after 7 days of inoculation of Fusarium oxysporum isolate spore. All the Trichoderma isolates showed maximum mycelial growth on MEA and minimum mycelial growth on CDA. From the three tomato varieties, Miya variety was more susceptible to Fusarium oxysporum isolate infection than both Cochoro and Fetane varieties. The antagonistic effect of Trichoderma isolates culture filtrate on the test pathogen showed that Trichoderma isolate AUT9 exhibited the highest percent inhibition 66 % on the mycelial growth of test pathogen. Trichoderma isolates AUT8 and AUT10 showed percent inhibition of 61 and 58%, respectively on the mycelial growth of the test pathogen. The symptoms of wilt were observed after 60 days of sowing. All Trichoderma isolates achieved maximum mycelial growth at 250C and minimum mycelial growth at 150C. The effect of pH on the mycelial growth of Trichoderma isolates in vitro showed that Trichoderma isolate AUT8 showed maximum mycelial growth at pH 5.5 and Trichoderma isolate AUT9 showed maximum mycelial growth at pH 6.5.
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Keywords
Pathogen, Resistance, Pesticide, Symptom, Antagonism, Antibiosis