RESUMEN Para evaluar la eficiencia del control biológico ejercido por aislados nativos de Trichoderma spp. sobre Rosellinia sp. causante de la muerte de plantas de macadamia, se realizaron dos experimentos en el Laboratorio de Fitopatología de la FCA-UNA, San Lorenzo, Central y en el vivero San Joaquín, Caraguatay, Cordillera. Para las pruebas in vitro se obtuvieron 19 aislados de Trichoderma spp. de parcelas productoras de macadamia del Paraguay y se enfrentaron en cultivo pareado con Rosellinia sp. para medir su capacidad antagónica, utilizando el Diseño Completamente al Azar (DCA) con cinco repeticiones. Los resultados obtenidos permitieron seleccionar a los aislados GS18 (Itapuá), GS13 (Central), GS10 (Cordillera) para su evaluación in vivo. Para el segundo experimento en condiciones in vivo se utilizó el DCA, los tratamientos consistieron en T1: Testigo (sólo el patógeno), T2: Mezcla de aislados de Trichoderma spp. y T3: Carbendazim al 0,1%, con cinco repeticiones. Las plantas de macadamia de 12 meses fueron tratadas con los aislados de Trichoderma spp.. Transcurridas 2 semanas se infestó el sustrato de todas las plantas con propágulos de Rosellinia spp.. Se aguardaron otras 2 semanas que permitieron el establecimiento del patógeno y se aplicó Carbendazim al 0,1%. En las plantas testigo se constató 53% de incidencia de la enfermedad, en las tratadas con Trichoderma spp. 26%, y en las plantas tratadas con Carbendazim se verificó 7%. Se concluye que los aislados nativos Trichoderma spp. presentan potencial como agentes biocontroladores de Rosellinia sp. al reducir la incidencia de la enfermedad en condiciones in vivo.

ABSTRACT To evaluate the biological control exercised by native isolates of Trichoderma spp. on Rosellinia sp., responsible for the death of macadamia nut plants, two experiments were carried out at the Phytopathology Lab of the FCA-UNA, San Lorenzo, main campus and at the San Joaquín nursery, Caraguatay, Cordillera. For in vitro tests, 19 isolates of Trichoderma spp. were obtained from several macadamia growing plots in Paraguay. They were faced in matched crops with Rosellinia sp. to measure their antagonistic capacity, using a completely randomized design with five repetitions. The results allowed selecting the isolates GS18 (Itapua), GS13 (Central), GS10 (Cordillera) for their in vivo evaluation. For the second experiment, a completely randomized design was used. The treatments consisted on T1: Control (the pathogen only), T2: Trichoderma spp isolates mix. and T3: 1% Carbendazim having each one five repetitions. 12 months old Macadamia plants were treated with the Trichoderma spp isolates mix. After 2 weeks, the substratum of all plants was infested with Rosellinia sp. propagules, two more weeks were allowed to assure the establishment of the pathogen and then Carbendazim with 0,1% dose, was applied. In the control plants, it was observed a 53% incidence of disease, a 26% in the plants treated with the Trichoderma spp. mix and 7% in plants treated with Carbendazim. It is concluded that native isolates of Trichoderma spp. have a potential as Rosellinia sp .bio-control agents since they reduce the incidence of the disease in in vivo conditions.