Leaf Spot Characteristics of Phomopsis Durionis on Durian (Durio Zibethinus Murray) and Latent Infection of the Pathogen

A survey of leaf spot disease on durian caused by Phomopsis durionis was conducted in durian growing areas in eastern Thailand, Chanthaburi and Trat provinces. It was found that lesions with yellow halos on both mature and young leaves are variable in sizes (1–10 mm in diameter). In this study, nine morphologically distinct isolates of Phomopsis were obtained from durian leaf spots. Some of them produced small number of pycnidia on potato dextrose agar after incubation for 30 days. Artificial inoculation on wounded leaves of durian seedlings, resulted in the production of browning areas with yellow halos and pycnidium formation at 13 days and 20 days after inoculation, respectively. Furthermore, red-brown spots with yellow halos on leaf tissues were observed at 32 days after inoculation. High density of Phomopsis was observed in durian symptomless leaves and flowers indicated the latent infection of the pathogen in the fields. Interestingly, crude extract of durian leaf with preformed substances demonstrated inhibition of spore germination and germ tube growth of the pathogen, Phomopsis sp., on water agar. In addition, bioassay on TLC plate displayed inhibition zone of growth of the fungus, Cladosporium oxysporum at retention factor (Rf) of 0.29–0.88. This indicates that preformed substances in leaf tissues might act as compounds affecting latent period of pathogen.