Isakeit T, Black M C, Barnes L W, Jones J B
Department of Plant Pathology and Microbiology, Texas A&M University, Weslaco 78596.
Department of Plant Pathology and Microbiology, Texas A&M University, Uvalde 78802.
Plant Dis. 1997 Jun;81(6):694. doi: 10.1094/PDIS.1997.81.6.694C.
Honeydew fruits (Cucumis melo var. inodorus Jacq. 'Morning Ice,' 'Honeybrew,' and 'Green Flesh') with circular, 3- to 10-mm-diameter lesions that did not extend into the flesh of the fruit were collected from a field in Frio County, TX, in October 1996. Lesions were either water-soaked or had a scabby center with a water-soaked edge. Non-fluorescent, gram-negative bacteria were consistently isolated from lesions. Eleven representative bacterial strains had 0.835 to 0.950 similarity to Acidovorax avenae subsp. citrulli, using Biolog GN Microplates and the MicroLog data base release 3.50 (Biolog, Hayward, CA). Strains were tested for pathogenicity on watermelon (C. lanatus (Thunb.) Matsum. & Nakai 'Royal Sweet') and honeydew seedlings (cv. Morning Ice) by daubing suspensions (approximately 10 CFU/ml) of bacteria onto cotyledons of 1-week-old transplants. Water soaking, followed by necrosis, occurred after 3 to 5 days. A. avenae subsp. citrulli, the causal agent of bacterial fruit blotch of watermelon, was reisolated from lesions. Detached fruit of honeydew (various cultivars) and watermelon (cv. Emperor) were surface disinfested with 70% ethanol, injected sub-epidermally with bacterial suspensions in blemish-free areas, and incubated at 24°C. Water-soaked lesions developed on fruit 10 to 14 days later and the bacteria were reisolated from inoculated fruit. Fruit inoculated with sterile water did not develop symptoms. Female flowers of honeydew plants (cv. Honeybrew) were inoculated at the time of pollination with a suspension of bacteria daubed on the fruit surface. Pollinated fruits were sealed in a moist chamber for 48 h. Circular, water-soaked spots developed 10 to 14 days later. A. avenae subsp. citrulli was reisolated from these lesions. The affected 44-ha field utilized center pivot irrigation and the incidence of diseased fruit exceeded 50%. The source of the pathogen is unknown. Bacterial fruit blotch was identified in watermelon grown under overhead irrigation 0.8 km from this honeydew field 9 weeks earlier. In past years, bacterial fruit blotch has occurred in watermelon fields in Frio County (1). Honeydew from other fields in the vicinity, including one that was also sprinkler irrigated, did not show these symptoms. This is the first report of A. avenae subsp. citrulli causing a disease of honeydew fruit. Reference: M. C. Black et al. Plant Dis. 78:831, 1994.
1996年10月，从得克萨斯州弗里奥县的一块田地中采集了哈蜜瓜果实（甜瓜变种甜瓜‘晨冰’‘蜜酿’和‘绿肉’），果实上有直径3至10毫米的圆形病斑，病斑未深入果肉。病斑要么是水渍状的，要么有结痂的中心和水渍状的边缘。从病斑中始终分离出非荧光革兰氏阴性菌。使用Biolog GN微孔板和MicroLog数据库3.50版（Biolog，加利福尼亚州海沃德），11株代表性细菌菌株与燕麦嗜酸菌西瓜亚种的相似度为0.835至0.950。通过将细菌悬浮液（约10 CFU/ml）涂抹在1周龄移栽苗的子叶上，对西瓜（甜瓜（Thunb.）Matsum. & Nakai‘皇家甜心’）和哈蜜瓜幼苗（品种‘晨冰’）进行致病性测试。3至5天后出现水渍，随后坏死。从病斑中重新分离出西瓜细菌性果斑病的病原菌燕麦嗜酸菌西瓜亚种。将哈蜜瓜（多个品种）和西瓜（品种‘皇帝’）的离体果实用70%乙醇进行表面消毒，在无瑕疵区域皮下注射细菌悬浮液，然后在24°C下培养。10至14天后果实上出现水渍状病斑，从接种果实中重新分离出细菌。接种无菌水的果实未出现症状。在授粉时，用涂抹在果实表面的细菌悬浮液对接种哈蜜瓜植株（品种‘蜜酿’）的雌花进行接种。授粉后的果实密封在潮湿的培养箱中48小时。10至14天后出现圆形水渍斑。从这些病斑中重新分离出燕麦嗜酸菌西瓜亚种。受灾的44公顷田地采用中心支轴灌溉，病果发生率超过50%。病原菌的来源不明。9周前，在距离这块哈蜜瓜田0.8公里处采用顶喷灌溉种植的西瓜中发现了细菌性果斑病。在过去几年中，弗里奥县的西瓜田曾发生过细菌性果斑病（1）。附近其他田地的哈蜜瓜，包括一块也采用喷灌的田地，未出现这些症状。这是燕麦嗜酸菌西瓜亚种导致哈蜜瓜果实病害的首次报道。参考文献：M. C. Black等人，《植物病害》78:831，1994年。
