Studies on the endophytic mycota of Citrus spp.

摘要

An investigation has been undertaken to determine the pattern of colonisation of citrus fruit and branches by stem-end rot pathogens (Phomopsis citri, Lasiodiplodia theobromae,and Botryosphaeria sp). The healthy (symptomless) flowers, fruits, pedicels, and branches (five most recent growth flushes) of Citrus reticulata var 'Nin Kat' that had been regularly sprayed or not sprayed with copper oxychloride were assayed monthly for endophytic fungi over two consecutive seasons. All three stem-end rot pathogens were confirmed to be endophytes. Members of other genera (including known pathogens of Citrus)were also recovered as endophytes including Colletotrichum (anthracnose), GuignardialPhyllostictina (black spot), Mycosphaerella (greasy spot), Cladosporium, and Alternaria. Recovery levels of all fungi varied in time, reflecting the complex and dynamic nature of the host/colonist interactions. In addition. other plantings in China and elsewhere were sampled as opportunity permitted. A greater diversity of fungi was recovered from plant material collected from Chinese sites and unsprayed sites, suggesting that domestication (outside the native range of citrus) and the application of fungicides may reduce the prevalence and diversity of the endophytic mycota of fruit trees. The endophytic fungi present in healthy citrus tissues may represent a reservoir of: quiescent pathogens; potential pathogens; pathogen antagonists; insect repellents; harmless saprophytes; and host defence elicitors. It is in the last-named role that they merited consideration by this workshop. Endophytic colonists are present throughout tree growth and development. In any crop centre of origin,evolution may have favoured those endophytes that provided some natural selection advantage to the host. The advantages may have included the production of anti-microbials by the endophytic colonist or the elicitation of similar compounds by the host. Further studies are needed in the centres of origin of our major fruit species to seek and evaluate fungal colonists that might confer such advantages.