Development of Brown root disease in Sri Lankan rubber plantations: possible involvement of other tree species

Brown root disease caused by Phellinus noxius is becoming an important root disease of Sri Lankan rubber plantations. Hence, this study was conducted to identify the alternative host species of the pathogen and to determine the role of those species in the incidence and the severity of brown root disease in rubber plantations. Seventy brown root disease incidences were used to assess the host range and the disease transmitting pattern. A structured questionnaire was used to collect the background information from the growers and the extension officers. In association with the roots of the diseased rubber trees, roots/root pieces of twenty six alternative species were identified and pathogen was isolated from seven alternative species only. The signs and the symptoms of the collar and the root systems of rubber and the associated tree species were recorded. The pathogenicity of those cultures were proved by Koch’s postulates and the seven different isolates showed cross infection ability among the species from which they were isolated and with rubber. The seven isolates showed a variation in their morphological and growth characteristics. It was observed that in all the brown root disease incidences on rubber, the primary inoculum was from a non-rubber species and the land had been previously either under the forest or abandoned for years with trees and shrubs of forest origin. With the findings of the study, it was concluded that the infection of brown root disease to rubber in these areas has an association with the other tree species such as Cereya arborea, Gmelina arborea and Bridelia retusa in the root contact.