Destructive Leaf Rot Disease Caused by Fusarium oxysporum on Aloe barbadensis Miller in Bali

Aloe (Aloe barbadensis Miller) has been planted in Bali since 2006 with the total area of 170 hectares. There was a destructive leaf rot disease was found to be associated with aloe plants, however, there is no information available on the cause of the disease. This research was conducted in order to identify the causal agent that responsible for the leaf rot disease on aloe. The observation on the occurrence of the disease was done in five regencies in Bali, namely Buleleng, Karangasem, Bangli, Gianyar and Badung. Three observations point were determined in each regency by evaluating 20% of the total plant population in each observation point to determine the disease occurrences. Koch Postulate was applied to confirm the causal agent of the disease. Identification of the causal agent was done based on the morphological characteristics observed under Scanning Electron Microscope and molecular analysis of 18S rDNA. Results of this study showed that the leaf rot disease was found distributed in all five regencies of Bali, where the aloe is grown. The average incidence of the leaf rot disease was 7.35%. A pathogenic fungus, Fusarium sp. isolate Fo2010 was found to be the causal agent of the disease. Based on observation under scanning electron microscope and the analysis of 18S rDNA, the Fusarium sp. isolate Fo2010 was identified as Fusarium oxysporum with smooth surface macro conidia, intercalary, while the micro conidia and hypha were roughly. This is the first report of the leaf rot disease on A. barbadensis since its introduction to Bali in 2006. Key words: destructive disease, Aloe barbadensis, Fusarium oxysporum, 18S rDNA