Screening for the Isolates of Thrichoderma Viride Against Alternaria Alternata and Its Antagonistic Mechanism

By the method of baiting, 18 isolates were obtained, and further identificatied as Trichoderma viride.The antagonistic tests of all these isolates to 7 strains of Alternaria alternata from diseased tobacco leaves from different area of Yunnan were carried out by pairing culture on PDA.The results showed that 1 isolated (Tv-1)was strong antagonistic.The examination of antagonistic mechanism under optical microscope and transmission electron microscope showed Tv-1 hyphae growed quickly.Its hyphae could adhere to, coil around the hyphae of pathogen. Its finger-shaped haustorium penetrated into the hyphae of Alternaria alternat. Tv-1 could also secret antibiotic substance to make the pathogan hyphal plasma contracted, vacuolated and disrupted.