Etiology of white root disease of cashew (Anacardium occidentale L.)

White root disease is a significant disease of cashew in Indonesia. However, the identity of the causal agent of the disease remains unclear. The objective of the research was to determine the pathogen causing cashew white root disease. Procedures undertaken in this research were (1) field observation in cashew plantations in Karangasem, Bali; (2) isolation and characterization of the suspected fungus and (3) Koch’s postulate on cashew saplings in the greenhouse. Field observation showed that white root disease occurs in cashew plantations with trees prevalently at the age of 8-23 years, with the primary symptom wilting and the presence of rhizomorph on the basal stem. Morphologically, Rigidoporus sp. fungus was consistently isolated from the root of infected plants. An artificial inoculation on nine-month-old saplings showed that wilting symptoms and the presence of rhizomorph on the basal stem developed at 51-76 days after inoculation. The inoculated saplings finally died. Root colonization by Rigidoporus sp. ranged from 35-90%. Rigidoporus sp. as the causal agent of white root disease of cashew was confirmed.