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Transformants of Trichoderma longibrachiatum Overexpressing the β-1,4-Endoglucanase Gene egl1 Show Enhanced Biocontrol of Pythium ultimum on Cucumber

First, third, and fourth authors: Dipartimento di Valorizzazione e Protezione delle Risorse Agroforestali, Università di Torino, Via L. da Vinci 44, I-10095 Grugliasco, Torino, Italy; and second and fifth authors: Instituto de Agroquímica y Tecnologia de Alimentos, Apartado de Correos 73, E-46100 Burjassot, Valencia, Spain

Nine transformants of Trichoderma longibrachiatum with extra copies of the egl1 gene were studied for mitotic stability, endoglucanase production, and biocontrol activity against Pythium ultimum on cucumber seedlings. The transformants showed a significantly higher level of expression of the egl1 gene in comparison to the wild type under both inducing and noninducing growth conditions. Transformants with the egl1 gene under the control of a constitutive promoter had the highest enzymatic activity. Both the endoglucanase activity and the transforming sequences were stable under nonselective conditions. When applied to cucumber seeds sown in P. ultimum-infested soil, T. longibrachiatum transformants with increased inducible or constitutive egl1 expression generally were more suppressive than the wild-type strain.

Additional keywords: damping-off , biological control , lytic enzymes , rhizosphere .