New Record of Fusarium Leaf Spot Disease of Philodendron hastatum, an Ornamental Plant

Philodendron hastatum is also known as Silver Sword Philodendron due to its shiny, silvery leaf appearance and belongs to the family Araceae. It is known to be a perfect addition to the home decors as ornamental plant with high economic value all over the world. Necrotic spots were observed on the leaves of P. hastatum, at the plant sales centers and in the adjoining home gardens in Chenkalady, Batticaloa, Sri Lanka. Symptoms initiated as brownish, tan or black spots and enlarged with 3 to 5 mm diameter lesions on the adaxial of the matured leaves. No defoliation was observed due to this unknown disease and also no symptoms were observed on either on flowers or stem. Present study was conducted with the main objective of identifying fungal pathogen causing the leaf spots in P. hastatum, using morphological and molecular data. Fusarium was isolated from five leaves of three different P. hastatum plants, showing the lesions from the study area. The morphological data showed that an isolate was sparse to abundant cottony mycelium with colony color and pigmentations from pale white to light violet. Conidiophores are short, single, lateral mono phialides in the aerial mycelium that are later arranged in densely branched clusters. Macroconidia are fusiform, slightly curved, and pointed at the tip, with three septate basal cells and a size of 23-54 x 3-4.5 µm. Microconidia are abundant, never in chains, mostly non-septate, ellipsoidal to cylindrical, straight or often curved. The molesular data showed that the sequence of the fungal isolate was 99 % similar to the sequence with Accession Number AB369259, based on the BLAST search results with authenticated sequences. Thereby, the fungus associated with this leaf disease was identified as Fusarium oxysporum, based on the morphological and molecular data. Healthy inoculated P. hastatum leaves produced spot symptoms 7 days after the inoculation and they were similar to those observed originally on diseased leaves. The pathogenicity of the fungus was confirmed by performing the Koch’s postulates. This is recorded as the first report of Philodendron leaf spot, caused by Fusarium oxysporum, in Sri Lanka.