Identification And Pathopoiesia Mechanism Of A Pathogenic Achlya Klebsiana Strain From The Eggs Of Pelteobagrus Fulvidraco

Yellow catfish, Pelteobagrus fulvidraco, is a popular freshwater fish species in China due to its excellent meat quality and has brought a great profit in recent years. However, saprolegniasis is one of the most serious diseases in artificial hatching process of Yellow catfish eggs, influenced the process of seedling production scale, and causeed significant economic losses. Therefore, it is significant and necessary to carry out the identification and research pathopoiesia mechanism of a pathogenic. In June,2011Xian tao city artificial hatching of Yellow catfish eggs occurred serious saprolegniasis, caused a large number of fish eggs death, decreased hatching rate. As a result, a pathogenic strain YC was isolated and identificated by characteristics of morphological and molecular biological. Then determined the Chinese herbal medicine and the fungicide for its minimum bacteriostatic concentration, and preliminary studied the infection mechanism of saprolegniasis.The main results are as follows:1Identification of a pathogenic strain from the eggs of Yellow catfishEight filamentous fungal strains were isolated form the Pelteobagrus fulvidraco eggs suffering from saprolegniasis, and strain YC was proved to be pathogenic to Pelteobagrus fulvidraco eggs by artificial infection. Then, identified using morphological observation and phylogenetic analysis based on its ITS rDNA sequence. The experimental results showed that the hyphae of strain YC were aseptate and transparent, its zoosporangia were cylindrical, clavate or fusiform, its zoospores were discharged from the tip of zoosporangia, clumped together and fell off or directly swam into the water after a period of time. The zoosporangia were renewed in basipetalous succession, infrequently in sympodial arrangement. Its oogonia were spherical or obpyriform with frequently diclinous and occasionally monoclinous antheridial branches, and produced one to fifteen oospores, which were centric or subcentric, and laterally generated a big oil body. The ITS rDNA sequences of strain YC was naturally clustered with ITS rDNA sequences of Achlya sp. submitted to GenBank with the homology of99%, and had closest relationship with Achlya klebsiana strain CBS101.49(GenBank accession number:AF119579). Combined the morphological characterization with phylogenetic analysis based on ITS rDNA sequence, strain YC was identified as Achlya klebsiana.2Preservation of the pathogenic Achlya klebsianaA simple and effective preservation method was established for pathogenic Achlya klebsiana, which was as follows:sterilized rapeseeds with hyphae were set in4.8mL sterile distilled water or3.8mL sterile distilled water and1mL sterile sabouraud medium, then stored at4℃. The results indicated that the pathogenic Saprolegnia sp. and Achlya sp. could be effectively preserved for at least one year under this method, and their recovery rate arrived at100%. The simple and effective preservation method in this study was conducive to enrich the preservation method for pathogen of saprolegniasis.3Pathopoiesia mechanism of saprolegniasis on eggs by Achlya klebsianaThe aim of the study was to research the relationship between the concentration of saprolegnia spore and outbreak of saprolegniasis of eggs under different concentration, which could provide scientific theoretical basis of preventing saprolegnia for artificial inoculation of eggs. The fish eggs Saprolegniasis is infected by spores in water, and can be transmitted through horizontal; Under the conditions of the test, the hatch within48h, waters water mold spore suspension concentration have a close relationship with the incidence rates of the saprolegniasis within48h of hatching. The saprolegniasis infection rates increase with the increasing of the concentration of water mold spores, and significant differences between each concentration group; hatching the eggs after48h when the water mold spore concentration is above100spores/mL, the rate of infection of the saprolegniasis incidence is no longer significantly improved with the time delay of each concentration group; saprolegniasis began erupting in48-60h of incubation. It was the first time that the paper studied the relationship between the concentration of saprolegnia spores and outbreak of saprolegnia. It pointed out100spores/mL as a critical concentration during the artificial incubation and the saprolegnia started to outbreak after48-60h, which provided a theoretical basis for prevention and control of the disease.4In vitro screening drugs against growth of Achlya klebsianaStudy the drug susceptibility characteristics of the pathogenic Achlya klebsiana by doubling dilution method. The experimental results showed that:the hyp ha of strain YC was well inhibited by Coptis chinensis and Fungicide X, whose minimum inhibitory concentrations to strain YC were respectively256mg/L and0.5mg/L. Its drug susceptibility was also determined, which could serve as a foundation for its infection in Pelteobagrus fulvidraco eggs.