Abstract:

The primary objective of this study was to determine distribution patterns of endophytic Colletotrichum sp. in different tissues and different leaf ages of Camellia sinensis. Through artificial inoculation on detached leaves and fungifree seedlings, and re isolation, endophylism of the fungus in tea leaves was datermined. The results showed that endophytic endophytic Colletotrichum sp. was frequently isolated from tissue of healthy leaves and branches of tea plants. Colletotrichumsp. was isolated from 55.62% of leaf segments and the isolation ratio was 73.47% from the branches. However, in main root, stems, blossom and fruits, no colonization of endophytic Colletotrichum spp.was detected. Colletotrichumsp. was much less frequently isolated from newly flushed shoots of tea plants. The isolation rates grew gradually as the leaves developed. In mature leaves, the isolation ratio was 55.62%. But as the leaves developed further, the isolation rate dropped gradually. In artificial inoculation experiments, the conidia of Colletotrichum sp. germinated normally and formed mature appressoria on leaf surface. The fungi penetrated into leaf tissues directly between cuticle cells other than through trichome and stomatal openings. After entering host tissues, the fungus slowly colonized and had a limited growth which resulted in one or several fungal cells developed intercellularly or intracellularly in host tissues. Fungal penetration induced host cell defense responses in tea seedlings. In about 87% of fungal penetration sites, host cells reacted to fungal invasion by accumulating cytoplasm granules and forming papilla. Faint autoinfluorescence was also detected in some host cells which suggested that polyphenols accumulation occurred in those cells. In detached leaves, about 67.5% fungal penetration sites showed autoinfluorescence. Colletotrichum sp. was reintroduced into detached leaves and tea seedlings throught artificial inoculation. No obvious disease symptoms were observed 120 d after inoculation on tea seedlings. The fungus was recovered from all seedlings. The isolation ratio reached 41.17% from inoculated branches by spraying conidia suspension. The results indicated a feature of tissuespecific colonization of endophytic Colletotrichumsp. Artificial inoculation and microscopic observation strongly suggested that Colletotrichum sp. was an endophytic fungal species in tea plants. Cytoplasm aggregation and polyphenol accumulation were detected during the infection and colonization of host cells by Colletotrichumsp. The defense responses of host cells may contributed to the resulted endophytisum of Colletotrichum sp. in tea plants.
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Key words: Camellia sinensis, endophytic Colletotrichum sp., distribution, artificial inoculation, endophytisum