Pathogen Identifing Of Kiwifruit Bacterial Canker In China Main Produced Areas And Its Pathogenicity Test

Kiwifruit (Actinidia spp.), as a fruit tree origined in China, is mainly distributed in Chinese mountain areas. As an economic fruit tree cultivated, it need not a strict soil condition, easily adapt to the environment. Curently, kiwifruit had been widely planted under the reputation of ‘King of fruit’ for its rich Vitamin C content, a higher economic value and a unique flavor of fruit. However, Kiwifruit bacterial canker disease caused by Pseudomonas syringae pv. actinidae, spread fast and usually caused serious economic losses in most kiwifruit producing areas in the world in resent years. It was firstly discovered in Japan and United State of America, followed by South Korea and Italy. Recently, many reports were published, incloding in Chile, Portugal, Spain, Switzerland, New Zealand and France. In China, bacterial canker disease was firstly discovered in Hunan Province, then in Anhui, Shaan’xi and Sichuan Provinces. till now, it has been found and reported in ten-odd producing provinces.In this study, the diseased branches and leaves infected by bacterial canker were collected as material for pathogen isolation. Artificial inoculation method was used to test the pathogenicsity of isolated strains and select kiwifruit resistant cultivars. The inter space sequence of16S rDNA (16S rDNA-ITS) and the inter space sequence of16S-23S rDNA (16S-23S rDNA-ITS) were amplified and adopted for relationship between strains and their evolutionary trend. the achievement of this experiment will provid a basis for quick identification of kiwifruit canker and cultivar resistance evaluation.The main results had been gained as follows:1. By a survey of kiwifruit orchard in Anhui province (Yuexi county), Shaan’xi province (Hu county) and Chongqing municipality (Qianjiang county), we found that the pathogen of bacterial canker mainly infected trunks, damaged branches and leaves of kiwifruit. Milk-white exudates came out from diseased branch at primary stage, and then the exudates became russet. the new shoot on diseased branch wilted and then died. The typical symptom on leaf was a brown necrosis spot surrounded with a irregular yellow halo.2. The10isolates, coded as SXQM, SXHWD, A18, A17, C33, SXHY, AKA5, AKB5, AK14and AK18, were isolated from the kiwifruit tissues infected by bacterial canker. All isolates could cause allergy reaction to tobacco leaves and sickness to kiwifruit healthy leaves. The results of artificial inoculation test indicated that different pathogenic strains have different virulent to the same cultivar, accounting for different strains had different pathogenicity.3. The16S rDNA-ITS and16S-23S rDNA-ITS were cloned from10isolated and Italian standard strains at size of1500bp and300bp, after sequences analysis they were1448bp and280bp fragment, respectively. The Blast alignment online indicated that the obtained10strains was the same pathogen, and sequence of16S-23S rDNA-ITS was the same as the reported strain JN172920.1, HM032088.1, D86357.1and AY342165.1of Pseudomonas syringae pv. Actinidae, the accession number was JN629035and JQ314412in database of GenBank.4. The result of artificial inoculation on healthy leaves from different cultivars showed that ‘Jinyang’,‘Jinxiang’ and ‘Xiongzhu No2’, belong to Actinidea chinensis, were susceptible cultivars, while ‘Jinkui’ and ‘Xuxiang’, belong to Actinidea deliciousa, had stronger disease resistant ability.5. Cluster analysis of the isolated strain, the reported strains and other Pseudomonas syringae species according to16S rDNA-ITS, we found that the strain JN629035has closer relationship with the strain GQ914994, AB001439, EU906856and AJ889840, If cluster analysis made by16S-23S rDNA-ITS, JN172920.1, the strain JQ314412was in close relationship with strain HM032088.1, D86357.1and AY342165.1. Nevertheless P. syringae pv. actinidae could not be distinguished from P. syringae pv. theae by clusters analysis using16S rDNA or16S-23S rDNA-ITS.