| 我国有关核桃黑斑病的报道大都采用X.campestrispv.juglandis(Pierce)Dye。本研究将测得的核桃黑斑病菌16SrDNA进行BLAST分析，发现此细菌的16SrDNA序列与Xanthomonascampestris和X.arboricola一些致病变种的相似性为99%；另外经系统进化树表明该病原菌与X.populi、X.campestris、X.vesicatoria、X.theicola、X.Cucurbitae的典型株系进化关系最近，但致病变种的确定尚需进一步实验。
核桃黑斑病在我国发生较为普遍，一些核桃种植区发病严重。本文首次报道了核桃黑斑病在北京的发生为害。北京市近些年来为促进山区农村经济发展，在一些地区推广核桃栽培，并开始从我国一些核桃主产区调运苗木，这些调运的苗木可能携带核桃黑斑病菌，导致栽植当年或第二年发生核桃黑斑病。雨水和昆虫传播是该病发生流行的关键因素，所以在较为湿润的核桃种植区或雨水较多的年份，该病发生严重。2008年，北京春夏雨水多，山区林地小气候非常适宜昆虫活动和病菌传播，以致核桃黑斑病一经发生就迅速传播，导致一些地方发病率达40%，直接影响今后果树的生长。我们在调查中还发现，发病区周围生长的北京本地品种的老核桃树没有发生该病，说明北京当地品种可能对该病有一定的抗性。鉴于此，建议在引种苗木时，务必考察育苗地是否有该病害的发生为害，必要时做病原菌分离鉴定工作，明确苗木是否携带核桃黑斑病菌。
我国关于核桃黑斑病发生和防治的研究目前限于病菌的分离和防治试验。为进一步明确我国核桃黑斑病病原菌的分类地位，我们在研究中首先分离纯化了病原菌并进行了致病性实验，完成柯赫氏法则验证，然后提取核桃黑斑病病原细菌的总DNA，利用细菌16SrDNA的通用引物，采用PCR的方法扩增并克隆了核桃黑斑病菌的16SrDNA序列，测定了北京发生的核桃黑斑病病原菌16SrDNA序列，为从分子上进行病原菌鉴定和分类提供了数据。
国际上关于核桃黑斑病菌的命名尚有争论，最早被官方公认的名称为X.campestrispv.juglandis(Pierce)Dye(Dyeetal.,1980)，后来又被命名为X.arboricolapv.juglandis（Pierce）Vauterinetal.(Vauterinetal.,1995)，最近有提议将X.arboricola更换为X.juglandis(Pierce)Dowson(Schaadetal.,2000)。我国有关核桃黑斑病的报道大都采用X.campestrispv.juglandis(Pierce)Dye。本研究将测得的核桃黑斑病菌16SrDNA进行BLAST分析，发现此细菌的16SrDNA序列与Xanthomonascampestris和X.arboricola一些致病变种的相似性为99%；另外经系统进化树表明该病原菌与X.populi、X.campestris、X.vesicatoria、X.theicola、X.Cucurbitae的典型株系进化关系最近，但致病变种的确定尚需进一步实验。
致谢：感谢中国农业大学植物病理学系国立耘教授、张力群副教授在实验和写作中给予的指导帮助。
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