Fate of transformed Trichoderma harzianum in the phylloplane of tomato plants


  • This paper results from collaboration between the groups of Angelo Garibaldi (University of Torino) and Alfredo Herrera-Estrella (Centro de Investigacion y de Estudios Aianzados del I.P.N., Irapuato). Quirico Migheli., Maria Avataneo and M. Lodovica Gullino (Torino) a re involved in the improvement of the activity of antagonistic Trichoderma and Fusariiim spp. against foliar and soilbome fungal pathogens and in risk assessment studies for the release of genetically manipulated and nonmanipulated antagonistic fungi in the environment. Alfredo Herrera-EstTella has been working for several years in the development of fungal transformation systems and in molecular studies on the mechanism of action of Trichoderma spp. as mycoparasites, aiming to the development of improved strains by genetic engineering.

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A propiconazole-resistant Trichoderma harzianum strain with high phylloplane survival capability was transformed with the E. coli hygromycin B phosphotransferase gene (hph), coding for hygromycin B resistance. Four transformants were analysed for survival ability on the phylloplane of tomato plants grown under glasshouse conditions in comparison with their prototype and a yellow, hygromycin B-sensitive mutant. Over 2 weeks, the four transformants showed higher survival rates in comparison with the wild-type strain. The yellow mutant TF3/973 did not significantly differ in survival from the transformants. Both hygromycin B resistance and mitotic stability of transformants were evaluated during growth in vitro and after reisolation from tomato phylloplane. Hybridization patterns with the complete plasmid indicated that all four transformants were mitotically stable after several rounds of vegetative growth without selective pressure and during 2 weeks on tomato plants. None of the transformants had lost the ability to grow in the presence of both propiconazole and hygromycin B after growth under the same conditions. The results are discussed in relation to risk assessment of the release of transgenic fungi.