Isolation And Screening Of Phyllosphere Microorganisms Of Rehmannia Glutinosa And Studies On Their Mechanisms

Rehmannia glutinosa Libosch is a perennial herb of Scrophulariaceae, and has been cultivated for more than 1500 years. Its root is used frequently as a crude drug in traditional Chinese medicine. In the more concentrated cultivation areas,especially in the condition of continuous cropping, Rehmannia foliage fungal diseases are more serious.These disease are spot blight,ring spot and dot disease.Although the preliminary study on the pathogens of the foliage diseaseshas been done,pathogens are not identical because of the different geographical environments.Also, physical control and chemical control are taken to control these foliage diseases,the method of utilization of usefull microorganisms of the isolation and screenings of leaves from the disease region to control these diseases which is called biocontrol has not carried though.Therefore,in this dissertation,the study of the isolation and screening usefull microorganisms and their mechanisms will been done for the basic study of biocontrol of the foliage diseases by simplified experiments.The main findings are as follows:1.Thirty phyllosphere fungi were isolated from the leaves in the disease region,in which ten were from diseased leaves,twenty were from normal leaves. BY1,BY2 and BY3 were dominant species, BY1 belongs to Phllosticta Pers, BY2 belongs to Alternaria Nees. The proportion of BY1, BY2 and BY3 in the phyllosphere fungi of the disease leaves are respectively 33.3%,26.7%,20%.In the phyllosphere fungi of normal leaves,Penicillium,Aspergillus,Trichoderma are dominant genus.And,the quantity of phyllosphere fungi of old leaves is more than that of young leaves.2.After inoculating all of the phyllosphere fungi to the leaves of plantlets, unbodied leaves,the leaves of potted seedlings,I found that BY1 was the pathogen.I also found that BY10,DY5,DY15,DY16 had definite pathogenicity.In the experiment of inoculating all phyllosphere fungi to the leaves of plantlets, BY1, BY10, DY5, DY15,DY16 had the leaves caught a diseas,especially BY1,and the remaining fungi only brought small spots.In the experiment of unbodied leaves'test, BY1 brought spots fairly rapidly,thereafter,along with time'going, BY10, DY5, DY15,DY16 gave the brown rot to the leaves as a result of the extension of the mycelium.The remaining isolates except for DY9 brought brown rot as a result of the extension of the mycelium.In the test of potted seedlings,only BY1 brought spots,and the spots were expanding along with the extension of time,finally,the leaves seared and cracked.3.After in the standoff test between BY1and other isolates,I firstly got several usefull screenings,in which a few had the edge in nutrition and space competition, and they wereBY4,BY5,BY9,BY10,DY1,DY2,DY3,DY5,DY7,DY8,DY10,DY13,DY15,DY18, DY20.However, BY10,DY5,DY15 were eliminated from those usefull screenings because they had definite pathogenicity.At the same time, BY4, BY5, BY9, DY1,DY2,DY3,DY7,DY10,DY18,DY20 were antagonized by BY1,then they were out of the queue.Besides, BY9,DY1,DY2,DY3,DY7,DY10,DY18,DY20were difficult to colonize on the leaves,however, they could colonize on the leaves,they could not expand on the leaves rapidly,thus,these fungi died easily.And those screenings were mainly saprophytic fungi belonging to Penicilluim and Aspergillus,therefore,they were eliminated because of their bad parasitic ability. At last,the fungi that had the edge of competition were DY8,DY13. BY3, DY4, DY8,DY11,DY12 had antagonistic effects against BY1,then,filter paper-agar diffusion method and disc method were used for the further screening,and I found that BY3,DY4,DY11,DY12 had weaker antagonistic effects against BY1,and their inhibition rates were not more than 15%;at the same time,DY8 whose inhibition rate was nearly 40% had stronger antagonistic effects against BY1.However, the inhibition rate of BY3,DY4,DY11 and DY12 was nearly 30% in the standoff test,and the inhibition rate of DY8 was 65.6%.In the study of mechanism of the reproduction, DY8 had the stronger ability of reproduction than DY13.Finally I validated and confirmed usefull fungi by potted plant test,and I found that BY3, DY4, DY8, DY11,DY12,DY13 were usefull fungi,in which DY8 had stronger biocontrol capacity,and it could be an important biocontrol fungi for a further study.In conclusion,BY1 was the pathogen of the foliage disease in the disease region. BY1 that could colonized and expanded on the plantlet leaves,unbodied leaves and potted plant leaves cause foliage disease. BY3,DY4,DY8,DY11,DY12,DY13 were usefull screenings,in which BY3,DY4,DY8,DY11,DY12 had the mechanism of antagonism, DY8 and DY13 had the mechanism of competition and reproduction of pathogen.