Department of Plant Pathology and Microbiology, Iowa State University, Ames 50011, USA.
Phytopathology. 2013 Sep;103(9):900-5. doi: 10.1094/PHYTO-11-12-0301-R.
The causal agent of cucurbit bacterial wilt, Erwinia tracheiphila, has a wide host range in the family Cucurbitaceae, including economically important crops such as muskmelon (Cucumis melo), cucumber (C. sativus), and squash (Cucurbita spp.). Genetic variability of 69 E. tracheiphila strains was investigated by repetitive-element polymerase chain reaction (rep-PCR) using BOXA1R and ERIC1-2 primers. Fingerprint profiles revealed significant variability associated with crop host; strains isolated from Cucumis spp. were clearly distinguishable from Cucurbita spp.-isolated strains regardless of geographic origin. Twelve E. tracheiphila strains isolated from muskmelon, cucumber, or summer squash were inoculated onto muskmelon and summer squash seedlings, followed by incubation in a growth chamber. Wilt symptoms were assessed over 3 weeks, strains were reisolated, and rep-PCR profiles were compared with the inoculated strains. Wilting occurred significantly faster when seedlings were inoculated with strains that originated from the same crop host genus (P<0.001). In the first run of the experiment, cucumber and muskmelon strains caused wilting on muskmelon seedlings at a median of 7.8 and 5.6 days after inoculation (dai), respectively. Summer squash seedlings wilted 18.0, 15.7, and 5.7 dai when inoculated with muskmelon-, cucumber-, and squash-origin strains, respectively. In a second run of the experiment, cucumber and muskmelon strains caused wilting on muskmelon at 7.0 and 6.9 dai, respectively, whereas summer squash seedlings wilted at 23.6, 29.0 and 9.0 dai when inoculated with muskmelon-, cucumber-, and squash-origin strains, respectively. Our results provide the first evidence of genetic diversity within E. tracheiphila and suggest that strain specificity is associated with plant host. This advance is a first step toward understanding the genetic and population structure of E. tracheiphila.
蔓枯病的病原体丁香假单胞菌，在葫芦科中有广泛的宿主范围，包括甜瓜（Cucumis melo）、黄瓜（C. sativus）和南瓜（Cucurbita spp.）等经济重要作物。本研究采用重复元件聚合酶链反应（rep-PCR），使用 BOXA1R 和 ERIC1-2 引物对 69 株丁香假单胞菌的遗传变异进行了研究。指纹图谱显示与作物宿主有关的显著变异性；来自 Cucumis spp. 的菌株与来自 Cucurbita spp. 的菌株无论其地理来源如何都明显不同。从甜瓜、黄瓜或夏南瓜中分离出的 12 株丁香假单胞菌菌株接种到甜瓜和夏南瓜幼苗上，然后在生长室中培养。在 3 周内评估萎蔫症状，重新分离菌株，并将 rep-PCR 图谱与接种菌株进行比较。当幼苗接种来自同一作物宿主属的菌株时，萎蔫发生得更快（P<0.001）。在实验的第一轮中，黄瓜和甜瓜菌株分别在接种后 7.8 和 5.6 天导致甜瓜幼苗萎蔫。用来自甜瓜、黄瓜和南瓜的菌株接种夏南瓜幼苗时，夏南瓜幼苗分别在 18.0、15.7 和 5.7 天萎蔫。在实验的第二轮中，黄瓜和甜瓜菌株分别在接种后 7.0 和 6.9 天导致甜瓜萎蔫，而当用来自甜瓜、黄瓜和南瓜的菌株接种时，夏南瓜幼苗分别在 23.6、29.0 和 9.0 天萎蔫。我们的研究结果提供了丁香假单胞菌遗传多样性的第一个证据，并表明菌株特异性与植物宿主有关。这一进展是理解丁香假单胞菌遗传和种群结构的第一步。
