Renick Lisa J, Cogal Andrea G, Sundin George W
Department of Plant Pathology, Michigan State University, East Lansing 48824.
Plant Dis. 2008 Mar;92(3):372-378. doi: 10.1094/PDIS-92-3-0372.
A severe outbreak of bacterial canker occurred on sweet cherry in Michigan in 2002. Blossom infection and subsequent canker formation was observed following a prolonged freeze event during bloom. Epiphytic blossom isolates of Pseudomonas syringae were recovered from 39 orchards from the three major cherry-growing areas (southwest [SW], west-central [WC], and northwest [NW]) of Michigan in 2003 and 2004. Average P. syringae populations over 2 years were 4.0, 5.1, and 4.8 log CFU/g of blossom tissue from the SW, WC, and NW areas, respectively. In 2003, copper-resistant P. syringae comprised 47.4, 21.1, and 3.1% of the total populations from the SW, WC, and NW areas, respectively, and levels of copper resistance were similar in 2004. Identification of 10 randomly chosen isolates from each orchard using polymerase chain reaction (PCR) assays indicated that 75 and 52% of the isolates from 2003 and 2004, respectively were P. syringae pv. syringae and that 1% and 23% of the isolates from 2003 and 2004, respectively, were P. syringae pv. morsprunorum. In addition, we were unable to determine the pathovar status of approximately 25% of the isolates each year, suggesting that a third P. syringae pathovar also was present in Michigan sweet cherry orchards. Pathogenicity on immature cherry fruit was confirmed for all P. syringae isolates. The frequency of ice nucleation was assessed for 44 individual P. syringae pv. syringae isolates, and the mean number of cells per active ice nucleus was 1,883. Extrapolating from this result, we estimated that active ice nuclei are present on most sweet cherry blossoms in Michigan orchards. Genetic fingerprinting of P. syringae pv. syringae using arbitrarily primed PCR indicated a high level of diversity and a clear differentiation of these organisms from the P. syringae isolates of unknown pathovar. A 2-year field trial evaluating the effect of dormant copper applications in spring and reduced-rate copper applications prior to bloom showed that these treatments were inconsistent in reducing P. syringae populations on blossoms.
2002年，密歇根州的甜樱桃爆发了严重的细菌性溃疡病。在花期经历长时间的冻害事件后，观察到了花朵感染及随后溃疡的形成。2003年和2004年，从密歇根州三个主要樱桃种植区（西南部[SW]、中西部[WC]和西北部[NW]）的39个果园中分离出了丁香假单胞菌的附生花朵菌株。两年间，来自西南部、中西部和西北部地区的花朵组织中丁香假单胞菌的平均菌量分别为4.0、5.1和4.8 log CFU/g。2003年，耐铜丁香假单胞菌分别占西南部、中西部和西北部地区总菌量的47.4%、21.1%和3.1%，2004年的耐铜水平相似。使用聚合酶链反应（PCR）分析对每个果园随机选取的10个菌株进行鉴定，结果表明，2003年和2004年分别有75%和52%的菌株为丁香假单胞菌丁香致病变种，2003年和2004年分别有1%和23%的菌株为丁香假单胞菌李痘致病变种。此外，每年约有25%的菌株无法确定其致病变种状态，这表明密歇根州甜樱桃果园中还存在第三种丁香假单胞菌致病变种。所有丁香假单胞菌菌株对未成熟樱桃果实均具有致病性。对44个丁香假单胞菌丁香致病变种的单个菌株进行了冰核形成频率评估，每个活性冰核的平均细胞数为1883个。据此推断我们估计密歇根州果园中大多数甜樱桃花朵上都存在活性冰核。使用任意引物PCR对丁香假单胞菌丁香致病变种进行遗传指纹分析表明，这些菌株具有高度的多样性，并且与未知致病变种的丁香假单胞菌菌株有明显区别。一项为期两年的田间试验评估了春季休眠期施用铜制剂以及花期前减量施用铜制剂的效果，结果表明这些处理在减少花朵上丁香假单胞菌菌量方面效果不一致。
