Mello A F S, Yokomi R K, Melcher U, Chen J C, Wayadande A C, Fletcher J
Oklahoma State University, Department of Entomology and Plant Pathology, Stillwater 74078.
Phytopathology. 2008 Sep;98(9):960-8. doi: 10.1094/PHYTO-98-9-0960.
Spiroplasma citri, a phloem-limited pathogen, causes citrus stubborn disease (CSD). Losses due to CSD in California orchards have grown over the past decade. To investigate the possibility of introduction or emergence of a new strain, a study of genetic diversity among S. citri strains from various locations was conducted using random amplified polymorphism DNA-polymerase chain reaction (RAPD-PCR) of 35 strains cultured from 1980 to 1993, and of 35 strains cultured from 2005 to 2006. Analysis using 20 primer pairs revealed considerable diversity among strains. However, no unique genetic signatures were associated with recently collected strains compared with those collected 15 to 28 years ago, and no geographically associated pattern was distinguishable. S. citri strains from carrot and daikon radish contain some unique DNA fragments, suggesting some host plant influence. Multiple strains from single trees also showed genetic diversity. Sequencing of five RAPD bands that differed among strains showed that diversity-related gene sequences include virus fragments, and fragments potentially encoding a membrane lipoprotein, a DNA modification enzyme, and a mobilization element. No differences in colony morphology were observed among the strains. The lack of correlation between PCR patterns and isolation date or collection site is inconsistent with the hypothesis that recent infections are due to the introduction or emergence of novel pathogen strains.
柑桔螺原体是一种韧皮部受限病原体，可引发柑桔顽固病（CSD）。在过去十年中，加利福尼亚果园因CSD造成的损失不断增加。为了调查新菌株引入或出现的可能性，利用随机扩增多态性DNA聚合酶链反应（RAPD-PCR）对1980年至1993年培养的35个菌株以及2005年至2006年培养的35个菌株进行了研究，这些菌株来自不同地点。使用20对引物进行的分析显示菌株之间存在相当大的多样性。然而，与15至28年前收集的菌株相比，最近收集的菌株没有独特的遗传特征，也没有可区分的地理相关模式。来自胡萝卜和萝卜的柑桔螺原体菌株含有一些独特的DNA片段，表明宿主植物有一定影响。来自单株树的多个菌株也显示出遗传多样性。对菌株间不同的五个RAPD条带进行测序表明，与多样性相关的基因序列包括病毒片段，以及可能编码膜脂蛋白、DNA修饰酶和移动元件的片段。在这些菌株之间未观察到菌落形态的差异。PCR模式与分离日期或收集地点之间缺乏相关性，这与近期感染是由于新病原体菌株的引入或出现这一假设不一致。
