| Chinese cabbage soft rot is the main disease in the late stage of Chinese cabbage,also known as water rot and rot,which occurs in various regions.With the gradual expansion of production area and continuous planting,the disease has gradually spread in the main producing areas.Pectobacterium carotovorum subsp.carotovorum(Pcc)is usually considered to be the pathogenic bacteria of Chinese cabbage soft rot.A new disease with a similar soft rot condition was discovered in Harbin,Heilongjiang Province,China.The rot spots were first observed at the base of the petiole of the outer leaves,developed and enlarged,and even the whole plant rotted.Different from the symptoms of soft rot caused by Pcc,the rot is darker,has no obvious odor,and the rib fiber breaks down slowly.The shortened stem is not easy to rot and easy to grow side buds.The main purpose of this study was to identify the pathogenic bacteria of Chinese cabbage soft rot in Harbin through conventional and molecular methods,and to carry out pathogenicity test and resistance identification methods.The results are as follows:(1)By identifying the colony characteristics,gram staining and flagellar staining of five pathogenic bacteria strains isolated from soft rot of Chinese cabbage in Harbin and its surrounding areas,it was determined that the new pathogen of Chinese cabbage soft rot belongs to Pantoea.(2)The five strains were tested for pathogenicity.The disease of the plants inoculated with strains 1,3 and 5 were the same as the Chinese cabbage soft rot in the field,while the pathogens of strains 2 and 4 were slightly different.So strains 1,3,5 are p robably the pathogenic bacteria of Chinese cabbage soft rot.(3)Molecular identification of five pathogenic bacteria was carried out by using 16 S r DNA,DNA gyrase subunit B(gyr B)gene and rpo D gene,and it was confirmed that strains 1,3 and 5 were Pantoea agglomerans,and strains 2 and 4 were Pantoea ananatis.And the Gen Bank accession number of No.1,3 and 5 strains 16 S r DNA sequences were MK335467,MK335468 and MK335469;based on the gyr B gene and the rpo D gene sequence Gen Bank accession numbers MK439934,MK439935,MK439936 and MK439937,MK439938,MK439939.(4)The physiological and biochemical characteristics of Pantoea agglomerans were identified: 1)The optimum temperature for growth was 30°C,and the lethal temperature was 41°C.2)Gram reaction is negative;flagella: weekly whip;facultative anaerobic,no ga s fermentation;colony may or may not produce yellow pigment.3)can use D-ribose,D-mannitol,D-fructose and trehalose to produce acid.4)can use sucrose and glucose as a carbon source,can not use nitrate as a nitrogen source.5)The oxidase activity of the strain was determined to be negative;the hydrogen peroxide test was positive;hydrogen sulfide was formed;and the methyl red reaction was negative.(5)The resistance identification methods of Chinese cabbage Pantoea agglomerans were built.The method of inoculation with wound drip is more susceptible to disease;the optimal inoculum concentration of the bacterial suspension is 1012/m L;the optimal inoculation temperature is 30 °C/night 25 °C;the optimal inoculation age is the leaves of Chinese cabbage at the stage of seven/eight leaves;the humidity is 90-100% is the best. |
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