Exobasidium diseases occurring on camellias in Korea
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Nine species of Exobasidum have been reported from commercially grown tea trees (Camellia sinensis), tea-oil camellias (C. oleifera), Japanese camellias (C. japonica), and sasanqua camellias (C. sasanqua) worldwide. Among them, Exoabasidium vexans is one of the most damaging pathogens to commercial tea trees causing yield losses of up to 33 percent, when uncontrolled. Three of Exobasidium species have been reported on Camellia species in Korea: E. vexans on C. sinensis, E. gracile on C. sasanqua, and E. camelliae on C. japonica. Exobasidium gracile was first discovered and described on C. sasanqua in Korea in 2012. New leaves emerging from the infected trees were pale-green or tinged red, enlarged, and thickened compared to dark-green, normal leaves. E. gracile had a unique feature of growth that formed its hymenium layer in the intercellular spaces in the fourth to sixth cell layers above the abaxial leaf epidermis. The cell layers including the abaxial epidermis were sloughed off as basidia matured. Then, the exposed underside of the leaves was covered with white, powdery fungal growth which consisted of hyphae, basidia, basidiospores, and conidia. Exobasidium camelliae was reported to cause fruit galls on C. japonica in 2021. Infected fruits were enlarged, up to 3-6 cm in diameter, and the pericarp became thick and fleshy. When the gall matured, the fruit epidermis ruptured and peeled away exposing affected mesocarp tissues. The exposed surface was wrinkled and initially light green, but eventually became covered by a white hymenium layer. The two Exobasidium species were identified based on morphological characteristics and internal transcribed spacer and large-subunit rDNA sequence analyses. Camellia japonica occurs only as small and isolated populations on several southern islands in Korea, nine of which have been designated as natural monuments to prevent any disturbances. Precautionary monitoring of Exobasidium diseases would be a significant part of the conservation efforts of Korean populations of C. japonica.
Keywords: Adaptive and integrated management, Research, Sustainable forest management
ID: 3622507