Biodiversity Of Antagonistic Endophytic Actinomycetes From Ginkgo Biloba And Etiological Study Of Lactuca Sativa Leaf Blight

The thesis includes two parts: Isolation of antagonistic endophytic actinomycetes and their biodiversity study; Etiological study of a new disease on Lactuca sativa.Part one:Endophytes are microbes living asymptomatically, either the whole or part of their life cycles inside plant tissues, which include fungi, bacteria and actinomycetes. Study shows that endophytic actinomycetes can not only enhance plants growth and bring productivity improvement, but also colonize and propagate within plant tissues, in which they produce antagonistic substances such as antibiotics, enzymes and siderophores, inducing systematic defense responses of plants. Ginkgo biloba is one of the special trees in our country, it is well known for its disease resistance, which indicates the harmonious symbiosis of its endophytes with their host has played an important role in resisting the infection of pathogens. This paper is to study on the biodiversity of Ginkgo biloba endophytic actinomycetes varieties and screening antagonistic activities in Petri dishes, we hope to provide more potential biological control agents for ecological agriculture, and obtain some basic information for further effective using endophytes of Ginkgo biloba.Through sterilization the surface of leaves and fruits from Ginkgo biloba , isolation of endophytic actinomycetes and description of morphological characteristic, we got the results as follows: the total number of the isolates is 80, in which 60 strains came from the leaves, the rest from the fruits, the ratio is 3:1. The size of the colonies is different, the morphological characteristic difference is significant and the color of the colonies is varied, which showed abundant biodiversity of endophytic actinomycetes from Ginkgo biloba.High ratio of active strains was obtained through inhibitory activity screening. 51 active strains were obtained by inhibitory activity in vitro, and they had different antagonism to all provided pathogens, 96.2% to the whole selected isolates; 15 strains have high antagonistic activities and broad inhibition spectrum, 28.3% to all provided isolates. Screening of the crude fermentation products showed that all products had very high antagonism (the inhibition zone diameters are over 20mm) to some of the pathogens, and the activity of the products was accorded to their strains in vitro, which indicated that Ginkgo biloba endophytic actinomycetes are hopeful candidate as biocontrol agents, they have potential applied value.