Dutta Bhabesh, Gitaitis Ronald D, Webster Theodore M, Sanders Hunt, Smith Samuel, Langston David B
Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 31793-0748.
Crop Protection and Management Research Unit, United States Department of Agriculture-Agricultural Research Service, Tifton, GA 31793-0748.
Plant Dis. 2014 May;98(5):660-666. doi: 10.1094/PDIS-10-13-1077-RE.
Yellow bud, caused by Pseudomonas sp., is an emerging bacterial disease of onion. A polymerase chain reaction assay based on the coronafacate ligase (cfl) and HrpZ genes was used to detect initial suspected bacteria on weeds. Growth on an agar medium, ability to cause a hypersensitive response in tobacco, pathogenicity on onion, and sequence analysis of 16S ribosomal RNA and cfl genes were used to confirm the identity of Pseudomonas sp. recovered from 10 asymptomatic weed species in the Vidalia onion-growing zone (VOZ) of Georgia. Among the weeds identified as epiphytic hosts for Pseudomonas sp., Italian ryegrass (Lolium multiflorum) and curly dock (Rumex crispus) were prominent because ≥73% of the samples from five sample sites were positive for the bacterium. These weeds are commonly found throughout Georgia and, thus, were selected to assess their role in yellow bud epidemiology. Samples of the two weed species were collected from sites along the perimeter of and within the VOZ (n = 5 sites) during late June, August, and September 2012 and 2013, which represented the time interval between onion growing seasons. Samples (n = 10/weed species/site) were collected and processed for bacterial detection as described above. In June (2012 and 2013), Pseudomonas sp. was detected from Italian ryegrass and curly dock in 100 and 40% of the sample sites, respectively. During the months of August and September (2012), the bacterium was recovered from Italian ryegrass in 60 and 10% of the sample sites, respectively; whereas, in August (2013), Pseudomonas sp. was recovered from 40% of the sample sites. However, the bacterium was not recovered from any of the sites in September (2013). In contrast, during August and September (2012), Pseudomonas sp. was recovered from curly dock in 20 and 80% of the sample sites, respectively. Similarly, in August and September (2013), the bacterium was detected from 40 and 100% of the sample sites, respectively. These data demonstrated that the Pseudomonas sp. responsible for yellow bud can survive as an epiphyte on Italian ryegrass and curly dock between onion crops. Furthermore, using artificially infested onion seed, we demonstrated that Pseudomonas sp. can be transmitted through contaminated seed.
由假单胞菌属引起的黄芽病是一种新出现的洋葱细菌性病害。基于冠菌素连接酶（cfl）和HrpZ基因的聚合酶链反应分析用于检测杂草上最初疑似的细菌。通过在琼脂培养基上生长、在烟草中引发过敏反应的能力、对洋葱的致病性以及16S核糖体RNA和cfl基因的序列分析，来确认从佐治亚州维达利亚洋葱种植区（VOZ）的10种无症状杂草物种中分离出的假单胞菌属的身份。在被确定为假单胞菌属附生宿主的杂草中，意大利黑麦草（多花黑麦草）和皱叶酸模尤为突出，因为来自五个采样点的样本中≥73%对该细菌呈阳性。这些杂草在佐治亚州各地普遍存在，因此被选来评估它们在黄芽病流行病学中的作用。在2012年和2013年6月下旬、8月和9月期间，从VOZ周边和内部的地点（n = 5个地点）采集了这两种杂草的样本，这些时间代表了洋葱生长季节之间的时间间隔。按照上述方法采集样本（每种杂草每个地点n = 10）并进行处理以检测细菌。在6月（2012年和2013年），分别从100%和40%的采样点的意大利黑麦草和皱叶酸模中检测到假单胞菌属。在8月和9月（2012年）期间，分别从60%和10%的采样点的意大利黑麦草中分离到该细菌；而在8月（2013年），从40%的采样点分离到假单胞菌属。然而，在9月（2013年）没有从任何地点分离到该细菌。相比之下，在8月和9月（2012年）期间，分别从20%和80%的采样点的皱叶酸模中分离到假单胞菌属。同样，在8月和9月（2013年），分别从40%和100%的采样点检测到该细菌。这些数据表明，导致黄芽病的假单胞菌属可以在洋葱作物之间作为附生菌在意大利黑麦草和皱叶酸模上存活。此外，通过人工感染洋葱种子，我们证明假单胞菌属可以通过受污染的种子传播。
