du Toit L J, Derie M L, Hsiang T, Pelter G Q
Washington State University, Mount Vernon Research and Extension Unit, 16650 State Route 536, Mount Vernon 98273.
Department Environmental Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
Plant Dis. 2002 Oct;86(10):1178. doi: 10.1094/PDIS.2002.86.10.1178C.
Nine fields direct-seeded with onion (Allium cepa L.) were surveyed in central Washington in the spring and summer of 2001 for Botrytis species associated with onion seed crops produced in this semiarid region. Forty plants were sampled from each field in a 'W' pattern in April, and 20 plants were similarly sampled from each field in June and July. Each plant was placed in a separate plastic bag, stored at 4 ± 2°C for 3 to 5 weeks, sliced lengthwise using a knife sterilized with 70% ethyl alcohol, incubated in a moist chamber for 5 days, and examined under a dissecting microscope. Fungal growth resembling Botrytis spp. was transferred to acidified potato dextrose agar (PDA) for species identification based on colony morphology, rate of growth, and spore and sclerotium characteristics (3). Cultures were incubated on a laboratory bench at 24 ± 4°C with 8 to 16 h of daylight. A species resembling B. porri (3) was detected in 3 fields in April at an incidence ranging from 3 to 28%, and in 2 of the same 3 fields in each of June and July at incidences ranging from 5 to 10%. Infected plants were asymptomatic at the time of sampling. The isolates formed brown, cerebriform sclerotia and sporulated sparsely. Subsamples of seed harvested from each field were assayed for Botrytis spp. To detect internal infection, 400 seeds from each of the nine fields were soaked in 0.525% NaOCl for 60 s, triple-rinsed in sterile deionized water, air dried, placed on a selective agar medium (2) with 20 seed per 9-cm-diameter petri plate, and incubated at 24°C (12 h day/night) for 14 days. Seeds were examined 5, 10, and 14 days after plating, and fungi resembling Botrytis spp. were transferred to acidified PDA for species determination. Isolates resembling B. porri were detected in 0.75% of seed from two of the three fields in which this species was isolated from plant samples. The internal transcribed spacer 1 region of ribosomal DNA of four isolates of the putative B. porri (two from plant samples and two from seed) were sequenced, and all four sequences matched that of B. porri registered in GenBank (Accession No. Z99666) most closely. Botrytis porri is a pathogen of garlic (A. sativum L.), leek (A. porrum L.), and wild garlic (A. vineale L.), but can infect onion and shallot (A. ascalonicum L.) when inoculated on these hosts (1). To our knowledge, this is the first report of natural infection of onion by B. porri, and the first report of seedborne B. porri on onion. References: (1) W. R. Jarvis. Pathology. Page 62 in: Botryotinia and Botrytis Species: Taxonomy, Physiology, and Pathogenicity. Canada Department of Agriculture, Monograph No. 15, 1977. (2) G. Kritzman and D. Netzer. Phytoparasitica 6:3, 1978. (3) A. H. Presly. Plant Pathol. 34:422, 1985.
2001年春夏季，对华盛顿州中部9块直播洋葱（葱属植物）的田地进行了调查，以研究与该半干旱地区洋葱种子作物相关的葡萄孢属真菌种类。4月，在每块田地以“W”形模式采集40株植株样本，6月和7月，在每块田地同样采集20株植株样本。将每株植株置于单独的塑料袋中，在±2°C下储存3至5周，用70%乙醇消毒的刀纵向切片，在潮湿培养箱中培养5天，然后在解剖显微镜下检查。将类似葡萄孢属真菌的生长物转移至酸化马铃薯葡萄糖琼脂（PDA）上，根据菌落形态、生长速率以及孢子和菌核特征进行种类鉴定（3）。培养物在实验室工作台上24±4°C、光照8至16小时的条件下培养。4月，在3块田地中检测到一种类似葱葡萄孢（3）的真菌，发病率为3%至28%，6月和7月，在这3块田地中的2块中再次检测到，发病率为5%至10%。采样时，受感染植株无症状。分离物形成褐色、脑状菌核，产孢稀疏。对从每块田地收获的种子子样本进行葡萄孢属真菌检测。为检测内部感染，将9块田地中每块田地的400粒种子浸泡在0.525%次氯酸钠中60秒，在无菌去离子水中冲洗3次，风干，置于选择性琼脂培养基（2）上，每9厘米直径的培养皿中放20粒种子，在24°C（12小时光照/12小时黑暗）下培养14天。播种后5天、10天和14天检查种子，将类似葡萄孢属真菌的菌株转移至酸化PDA上进行种类鉴定。在从植株样本中分离出该种真菌的3块田地中的2块中，0.75%的种子检测到类似葱葡萄孢的分离物。对4株假定的葱葡萄孢分离物（2株来自植株样本，2株来自种子）的核糖体DNA内部转录间隔区1区域进行测序，所有4个序列与GenBank中登记的葱葡萄孢（登录号Z99666）序列匹配度最高。葱葡萄孢是大蒜（蒜）、韭菜（韭葱）和野蒜（野葱）的病原菌，但接种在这些寄主上时可感染洋葱和葱头（葱）（1）。据我们所知，这是关于葱葡萄孢对洋葱自然感染的首次报道，也是关于洋葱种子携带葱葡萄孢的首次报道。参考文献：（1）W.R.贾维斯。病理学。载于《葡萄孢盘菌属和葡萄孢属真菌：分类学、生理学和致病性》第62页。加拿大农业部，专论第15号，1977年。（2）G.克里茨曼和D.内策尔。《植物寄生》6:3，1978年。（3）A.H.普雷斯利。《植物病理学》34:422，1985年。
