Balestra G M, Sechler A, Schuenzel E, Schaad N W
Dipartimento di Protezione delle Piante, Università della Tuscia, 01100 Viterbo, Italy.
USDA, Foreign Disease-Weed Science Research Unit, Ft. Detrick, MD.
Plant Dis. 2008 Jun;92(6):981. doi: 10.1094/PDIS-92-6-0981C.
Xanthomonas citri (synonym = Xanthomonas axonopodis pv. citri) (3) has been reported in several countries in Africa (1) but not Somalia. During 2006 and 2007, hyperplasia-type lesions, often surrounded by a water-soaked margin and yellow halo, typical of citrus canker caused by X. citri were found on 8- to 10-year-old lime (Citrus limetta) and grapefruit (Citrus × paradisi Macfed.) trees in northern and southern Somalia, respectively. Ten leaf samples diagnosed presumptively as citrus canker by Xac ImmunoStrip test kits (Agdia, Elkhart, IN) were mailed to the USDA Foreign Disease-Weed Science Research Unit at Ft. Detrick, MD. To confirm the identification of X. citri, isolations were made from several lesions from each sample onto yeast-dextrose-CaCO (YDC) agar (2). Yellow, xanthomonad-like mucoid, convex colonies were purified and stored on YDC slants. Phenotypic tests were done as described (2), and real-time PCR assays were done using primers XCit8F and XCit5R with probe XCitP2 (N. W. Schaad, unpublished). For pathogenicity tests, cultures were grown overnight in liquid nutrient broth-yeast (4) medium adjusted to contain 1 × 10 CFU/ml and inoculated into leaves of lime seedlings with the blunt end of a 2-ml syringe. After 21 to 30 days in a lighted dew chamber (Model I-60DLM; Percival Scientific, Inc. Perry, IA) at 30/23°C day/night, symptoms were recorded. Cultures of sample S-1 (northern Somalia) from lime were phenotypically atypical of X. citri, PCR negative, and nonpathogenic. However, cultures of samples 3 to 7 (southern Somalia) from grapefruit were typical of X. citri and PCR positive; cultures 3 and 4 were tested for pathogenicity and produced erumpent lesions on lime. Isolations onto YDC agar resulted in typical mucoid, convex, yellow, PCR-positive colonies. To our knowledge, this is the first report of X. citri on citrus plants in Somalia. Strains S3 and S4 have been deposited in ICPB at Ft. Detrick, MD as ICPB 11650 and 11651, respectively. References: (1) J. F. Bradbury. Guide to Plant Pathogenic Bacteria. CAB International, Egham, UK, 1986. (2) N. W. Schaad et al. Xanthomonas. Page 175 in: Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. N. W. Schaad et al. eds. American Phytopathological Society, St. Paul. MN. 2001. (3) N. W. Schaad et al. Syst. Appl. Microbiol. 29:690, 2006. (4) A. K. Vidaver. Appl. Microbiol. 15:1523, 1967.
柑橘溃疡病菌（同义词 = 柑橘溃疡病菌致病变种）(3) 在非洲的几个国家均有报道(1)，但索马里没有。在2006年和2007年期间，分别在索马里北部和南部8至10年生的酸橙（枸橼酸橙）和葡萄柚（葡萄柚× paradisi Macfed.）树上发现了增生型病斑，病斑通常被水渍状边缘和黄色晕圈包围，这是由柑橘溃疡病菌引起的柑橘溃疡病的典型症状。用Xac免疫试纸检测试剂盒（Agdia公司，美国印第安纳州埃尔克哈特）初步诊断为柑橘溃疡病的10份叶片样本被邮寄到位于马里兰州德特里克堡的美国农业部外来病害 - 杂草科学研究单位。为了确认柑橘溃疡病菌的鉴定结果，从每个样本的几个病斑中分离菌株，接种到酵母 - 葡萄糖 - 碳酸钙（YDC）琼脂上(2)。纯化黄色、类黄单胞菌的黏液状、凸起菌落，并保存在YDC斜面上。按照所述方法进行表型测试(2)，并使用引物XCit8F和XCit5R以及探针XCitP2进行实时PCR检测（N. W. 沙德，未发表）。对于致病性测试，将培养物在调整为含有1×10 CFU/ml的液体营养肉汤 - 酵母(4) 培养基中过夜培养，并用2 ml注射器的钝端接种到酸橙幼苗的叶片中。在30/23°C日/夜的光照露水培养箱（型号I - 60DLM；Percival Scientific公司，美国爱荷华州佩里）中培养21至30天后，记录症状。来自酸橙的样本S - 1（索马里北部）的培养物在表型上不是柑橘溃疡病菌的典型特征，PCR检测为阴性，且无致病性。然而，来自葡萄柚的样本3至7（索马里南部）的培养物是柑橘溃疡病菌的典型特征且PCR检测为阳性；对培养物3和4进行致病性测试，在酸橙上产生了隆起的病斑。接种到YDC琼脂上分离得到典型的黏液状、凸起、黄色、PCR阳性菌落。据我们所知，这是柑橘溃疡病菌在索马里柑橘植株上的首次报道。菌株S3和S4已分别作为ICPB 11650和11651保藏于马里兰州德特里克堡的ICPB。参考文献：(1) J. F. 布拉德伯里。《植物病原细菌指南》。CAB国际出版社，英国伊格姆，1986年。(2) N. W. 沙德等人。《黄单胞菌属》。载于《植物病原细菌鉴定实验室指南》第3版，第175页。N. W. 沙德等人编著。美国植物病理学会，明尼苏达州圣保罗。2001年。(3) N. W. 沙德等人。《系统与应用微生物学》29:690，2006年。(4) A. K. 维达弗。《应用微生物学》15:1523，1967年。
