Abstract

Biocontrol of Rhizoctonia solani in tomato with Trichoderma harzianum mutants Jaime Montealegre1 , Luis Valderrama1 , Rodrigo Herrera1 , Ximena Besoaín2 , Luz M. Pérez3 1 Departamento de Sanidad Vegetal, U. de Chile; 2 Pontificia U. Católica de Valparaíso; 3 U. Andrés Bell., Casilla 1004, Santiago, Chile, e-mail: [email protected] Abstract: Biocontrol of Rhizoctonia solani in glasshouse tomatoes was analysed using Trichoderma harzianum mutants. These were obtained from wild strains of T. harzianum (previously selected for their good biocontrol activity), after treatment with N-methyl-N-nitro-N-nitrosoguanidine (NG) or UV light A (320 nm) or C (256 nm). Pellets containing different Trichoderma strains and selected mutants (1.7 g pellet/L soil) were applied to a soil previously inoculated with R. solani AG 4 at transplant. Controls without Trichoderma and with added fungicide were compared with each wild strain and mutant. Evaluations considered canker formation, root growth, mortality and fresh and dry weight of tomato plants of cvs. 92.95 and Góndola. Also the persistence in soil under storage conditions at 22 and 5ºC was evaluated. Results showed that mutants controlled better R. solani than their corresponding wild strains. Th 12 A10.1, Th 11 A 80.1 and NG 7 were the best mutants for control of R. solani in cv. 92.95; while in the cv. Góndola were not observed statistical differences in the different strains. In general these results indicate that the mutants mentioned above are more efficient than their corresponding wild types for the control of R. solani under high pressure of disease in glasshouse conditions, and have a good persistence in the soil under storage conditions at 22 and 5ºC. Experiments under greenhouse conditions are being carried out.