Resumo

SIAMETO, E. N.; OKOTH, S.; AMUGUNE, N. O.  e  CHEGE, N. C. Molecular characterization and identification of biocontrol isolates of Trichoderma harzianum from Embu District, Kenia. Trop. subtrop. agroecosyt [online]. 2011, vol.13, n.1, pp.81-90. ISSN 1870-0462.

Species in the genus Trichoderma are important commercial source of several enzymes, biofungicides and growth promoters. The most common biological control agents of the genus are strains of T. harzianum, T .viride and T. viriens. In this study, sixteen selected isolates of T. harzianum from different land use types in Embu, Kenya were tested for antagonistic action against five soil borne phytopathogenic fungi (Rhizoctonia solani, Pythium sp, Fusarium graminearum, F. oxysporum f sp phaseoli and F. oxysporum f sp Lycopersici) using dual culture assay and through production of non-volatile inhibitors. Seven isolates were further characterized using RAPD-PCR procedure to determine genetic variability. All T. harzianum isolates had considerable antagonistic effect on mycelial growth of the pathogens in dual cultures compared to the control. Maximum inhibitions occurred in Pythium sp-055E interactions (73%).The culture filtrates obtained from Czapek's liquid medium reduced the dry weight (mg) of the mycelia significantly while those from the potato dextrose broth showed minimum inhibition growth. Pythium sp. was most sensitive compared to other pathogens. Genetic similarities generated using Jaccard's coefficient of similarity ranged from 0.231 to 0.857 for isolates 055E, 011E, 010E and 015E. Since all T. harzianum isolates evaluated were effective in controlling colony growth of the soil borne pathogens both in dual cultures and in culture filtrates they could be tried as a broad spectrum biological control agent in the green house and under field conditions.

Palavras-chave : Trichoderma harzianum; growth antagonism; genetic similarity RAPDs.

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