Isolation, Identification And Pathogenicity Analysis Of The Pathogenic Bacteria Of Pitaya Canker

Pitaya,also known as red dragon fruit,is a perennial tropical and subtropical fruit.In recent years,due to the adjustment of agricultural planting structure,the promotion and planting of a single commercial variety,unreasonable field management and fertilizer application,and the change of climatic conditions,pitaya canker has broken out in a large area in Pitaya planting areas in many provinces and is becoming more and more serious.In this study,three strains of Neocystidium dimidiatum,the pathogen of Pitaya canker,were isolated and their cellulase and pectinase activities were detected;The most pathogenic strain was selected to identify the disease resistance of pitaya fruit,and the activities of SOD,POD,PAL,CAT and PPO were observed after pitaya fruit was inoculated with the pathogen.The main results are as follows:1.The diseased pitaya branches were collected from Luodian County,Zhenfeng County,Guanling County,Zhenning County and Wangmo County in Guizhou Province.The pathogenic bacteria were isolated by tissue isolation method.Through the verification of Koch’s rule,19 strains of pathogenic bacteria were obtained.Through morphological and molecular biological identification,19 strains of pathogenic bacteria were identified as follows: 3 strains of Neocystidium dimidiatum,5 strains of Fusarium dimerum,1 strain of Fusarium oxysporum,1 strain of Bjerkandera adusta,1 strain of Fusarium asiaticum,1 strain of Trametes hirsuta,1strain of Plectosphaerella cucumerina,2 Colletotrichum gloeosporioides,1Dipodascus australiensis,1 Nigrospora sphaerica,1 Fusarium equiseti,1 Alternaria alternata;Among them,three new host pathogens were found on pitaya fruit:Fusarium asiaticum Z-16,Plectosphaerella cucumerina Z-14,Dipodascus australiensis X-79 and Trametes hirsuta X-30.2.The cellulase activity and pectinase activity of three strains of N.dimidiatum X-65,R,B-2-1 were detected.It was found that N.dimidiatum could produce pectinase and cellulase,and the enzyme activity remained at a high level.The observation results of the change of enzyme activity showed that R > X-65 > B-2-1.The results of pathogenicity analysis showed that R > X-65 > B-2-1.The stem of Pitaya was inoculated with N.dimidiatum R,which was the most pathogenic,and the activity of defense enzymes of the plant was detected.It was found that the activities of SOD,POD,PAL,CAT and PPO increased first and then decreased,but the period and amplitude of activity increase were different.The highest value of SOD appeared on the 6th day,the rising rate was slow,the highest value of PAL enzyme activity appeared on the 4th day,while the highest values of pod,cat and PPO appeared on the 2nd-3rd day.