Isolation And Identification Of The Pathogen Of Quinoa Leaf Spot In Sichuan As Well As Prevention And Cure

Quinoa(Chenopodium quinoa willd)belongs to the Chenopodiaceae,which has been planted from 5000 to 7000 years ago.It is an annual dicotyledonous plant which can be derived from South America as a food crop with rich nutritional value.In recent years,large-scale quinoa diseases have occurred in quinoa-growing areas.In this paper,field surveys were conducted in Sichuan,which showed quinoa leaf spot disease is one of the quite common quinoa diseases.The surveys also demonstrated the disease caused a serious impact on the growth and development of quinoa,leading to a decline in yield.In view of the rapid spread speed and the high incidence rate of quinoa leaf spot disease,the production and economic benefits of quinoa have been seriously affected in Sichuan.At present,research on the disease is still lacking all over the world,while this paper isolated and identified the pathogen of quinoa leaf spot disease,and conducted morphological and biological characteristics research on it.At the same time,preliminary screening of inhibitory strains against the pathogen of leaf spot disease was done.The specific content is as follows:Firstly,representative diseased plants were collected from Jintang,Shiling in Chengdu City and Xichang City,together with some other quinoa planting bases.Collected strains were obtained by tissue separation while the isolated strains were purified and cultured to obtain pure strains.The strains of pathogenic bacteria were screened and identified by Koch 's law.The pathogenic strains were also cultivated for DNA extraction by kits,which was amplified and sequenced by PCR using 16 S rDNA universal primers.The products were identified by Blast comparison where MAGE4.0,mainly by the software proximity method(NJ),was applied to build phylogenetic trees in order to trace the occurrence of pathogenic bacteria.Ten isolated strains were obtained from the experiment,two of which were identified as pathogenic bacteria.They were confirmed as pantoea agglomerans,while the phylogenetic tree showed they were from different subspecies of the same ancestor,and the homology reached 99%.Secondly,the effects of pathogenic bacteria on the germination of quinoa seeds were explored.In the experiment,the effects of temperature,pH and NaCl concentration on the growth characteristics of pathogenic bacteria were selected as influence factors.The results showed that the pathogenic bacteria completely inhibited the germination of quinoa seeds;the optimal growth pH of the pathogenic bacteria was 7.0;the optimal growth NaCl concentration was 0.9%;the optimal growth temperature was 28 ? while 55 ? could cause death on the bacteria.Ulteriorly,we isolated healthy leaf endophytes by tissue separation.Meanwhile,some soil microbial strains were isolated by dilution plate coating method.The strains were screened by the plate confrontation experiment to obtain the antagonistic antibacterial strains of Pantoea agglomerans.The results showed that the three of isolated endophytes had no inhibitory effect on Pantoea agglomerans;one of the 26 strains obtained from the soil had a certain inhibitory effect on it,which was initially identified as Bacillus subtilis.