2007 Volume 3 Pages 47-53
Longan (Dimocarpus longan Lour. cv. Daw) is one of Thailand's most important export fruits. This crop was confronted with a severe postharvest fungal rot disease problem. Examination of the surface appearance using a stereo-microscope showed that the fruit skin was rough and uneven. Under a scanning electron microscope, the surface of longan fruit consisted of scale and epidermal hairs, and in some areas the remnant of cuticle could be observed. Filamentous fungi were also observed. Many genera of fungi were isolated from the affected skin of harvested longans by a tissue transplanting method. These were Aspergillus, Cladosporium, Colletotrichum, Fusarium, Lasiodiplodia, Mucor, Penicillium Pestalotiopsis, Phomopsis, Rhizopus, Trichoderma, Verticillium and 7 unidentified genera. Each of the fungal isolates was inoculated onto the pericarp of the fruit for pathogenicity determination. The pathogenic ability examination showed that Lasiodiplodia and Pestalotiopsis, which were common molds found on the fruit skin, caused the most severe symptoms, e.g. the diseased fruit rotted rapidly. The most virulent isolate was identified as Lasiodiplodia theobromae based on its morphological characteristics and by DNA sequencing.
