Thomas Anna, Carbone Ignazio, Choe Kisurb, Quesada-Ocampo Lina M, Ojiambo Peter S
Center for Integrated Fungal Research Department of Entomology and Plant Pathology North Carolina State University Raleigh NC USA.
Department of Entomology and Plant Pathology North Carolina State University Raleigh NC USA.
Ecol Evol. 2017 Jul 3;7(16):6231-6246. doi: 10.1002/ece3.3194. eCollection 2017 Aug.
, the causal agent of cucurbit downy mildew (CDM), is known to exhibit host specialization. The virulence of different isolates of the pathogen can be classified into pathotypes based on their compatibility with a differential set composed of specific cucurbit host types. However, the genetic basis of host specialization within is not yet known. Total genomic DNA extracted from nine isolates of collected from 2008 to 2013 from diverse cucurbit host types ( var. , , and ) in the United States were subjected to whole-genome sequencing. Comparative analysis of these nine genomes confirmed the presence of two distinct evolutionary lineages (lineages I and II) of . Many fixed polymorphisms separated lineage I comprising isolates from , and from lineage II comprising isolates from spp. and . Phenotypic characterization showed that lineage II isolates were of the A1 mating type and belonged to pathotypes 1 and 3 that were not known to be present in the United States prior to the resurgence of CDM in 2004. The association of lineage II isolates with the new pathotypes and a lack of genetic diversity among these isolates suggest that lineage II of is associated with the resurgence of CDM on cucumber in the United States.
引起葫芦科霜霉病（CDM）的病原菌已知表现出寄主专化性。该病原菌不同分离株的毒力可根据其与由特定葫芦科寄主类型组成的鉴别寄主的亲和性分为不同致病型。然而，病原菌寄主专化性的遗传基础尚不清楚。从2008年至2013年在美国从多种葫芦科寄主类型（甜瓜变种、黄瓜、南瓜和西瓜）上采集的9个病原菌分离株中提取的全基因组DNA进行了全基因组测序。对这9个基因组的比较分析证实了病原菌存在两个不同的进化谱系（谱系I和谱系II）。许多固定的多态性将包含来自甜瓜、黄瓜和南瓜分离株的谱系I与包含来自南瓜属和西瓜属分离株的谱系II区分开来。表型特征表明，谱系II分离株为A1交配型，属于致病型1和3，在2004年美国葫芦科霜霉病再度流行之前在美国并不存在。谱系II分离株与新致病型的关联以及这些分离株之间缺乏遗传多样性表明，病原菌的谱系II与美国黄瓜上葫芦科霜霉病的再度流行有关。
