The Occurrence Regularity Of Bacterial Soft Rot Disease On Seleng Wormwood In Nanjing

Seleng wormwood(Artemisia sp.)，a perennial herb,has been a popular special vegetable since the 1990s in Nanjing for its rich nutritional value and good health benefits,but in recent years,it has been reported that severe soft rot symptoms occurred in seleng wormwood in the planting area and led a shrink of its cultivation and production.So,we conducted a survey of seleng wormwood soft rot and related researches on the occurrence regularity in Baguazhou in Nanjing.The causal pathogen was verified as P.carotovorum subsp.carotovorum by a series tests flowing the Koch’s rule,including organism isolation from the soft rotted seleng wormwood tissue,symptom observation and pathogen re-isolation after the isolates inoculated into the seleng wormwood,and by molecular analysis based on 16s rDNA from the isolates and assay of BIOLOG.In autumn and spring,the health looking plants of different species of seleng wormwood(A.apiacea and A.stelleriana)were collected in the disease occurrence area,the results from PCR with the primers designed by the house keeping genes of Pcc,FliA(RNA polymerase sigma-28 subunit)and RpoH(RNA polymerase sigma-32 subunit),revealed that the plants in autumn were latent infection but the plants in spring were all clear from the roots to the leaves.Meanwhile,the soil samples of different depths(0-5,6-10,11-15 cm)in the fields with seleng wormwood soft rot disease happened in last cultivation season were collected in spring in 2015,and total DNA was extracted for PCR as described before.The results showed that the cells of Pcc existed in different levels of the soil from the fields.Although the distinct symptoms always presented on the surface of the host plant within 16 h after inoculated with the strains of Pcc,but in this work,no symptoms appeared on the stems of seleng wormwood even the down ends of the stems were kept in the solution of Pcc over 28 days.It was found that no bacterial cell went up when the stem sections cuttaged in the media occupied by Pcc marked with GFP for 7 days,but when young branches and small leaves exhibited from the stem sections kept insertion in the media for 3 weeks,cells presented in the sections even the height of 9 cm up the solution by observation of fluorescence,and the strength of fluorescence was lower with the increase of the height.The cells of Pcc were survival for over 28 days after absorbed in the autoclaved base material pelhamite under 28 ℃ without any nutrition.The leaves and stem sections of the same phyllotaxy from different varieties of seleng wormwood,Artemisia apiacea and Artemisia stelleriana,were inoculated with Pcc,and the area of the lesions were measured.The results indicated that the disease processes on the former was slower than the later.