Identification and Molecular Characterizations of Neoscytalidium dimidiatum Causing Stem Canker of Red-fleshed Dragon Fruit (Hylocereus polyrhizus) in Malaysia

During the year 2008 to 2009, a new disease of stem canker was noticed in most red-fleshed dragon fruit (Hylocereus polyrhizus) plantations in Malaysia. The symptoms observed were small circular sunken orange spot, black pycnidia and rotted stem. This study was conducted to determine the occurrence of the stem canker on H.polyrhizus in Malaysia, subsequently to isolate, identify and characterize the fungal pathogen based on morphology and molecular characteristics and pathogenicity test. From the surveyed 20 plantations in Malaysia, stem canker was detected in all the plantations. A total of 40 isolates of Scytalidium-like fungus were isolated and identified as Neoscytalidium dimidiatum based on morphological characteristics and ITS region sequences, which showed 99% similarity to N.dimidiatum (FJ648577). From the phylogenetic analysis using maximum-likelihood tree, isolates of N.dimidiatum from stem canker of H.polyrhizus were grouped together and did not show any sequence variation. From pathogenicity test, all 40 isolates of N.dimidiatum were pathogenic causing stem canker on H.polyrhizus. To our knowledge, this is the first report of stem canker of H.polyrhizus caused by N.dimidiatum in Malaysia.