Cobb A C, Dillard H R
Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456.
Plant Dis. 1998 Aug;82(8):960. doi: 10.1094/PDIS.1998.82.8.960B.
A leaf spot was observed on cruciferous weeds growing in a cabbage field located in Geneva, NY, on 1 August 1996. The leaf spots on the weeds were dark gray to black in color and varied in size from pinpoints to 1 mm in diameter. The cabbage (Brassica oleracea L. var. capitata L.) was infected with Alternaria brassicicola (Schwein.) Wiltshire, the cause of Alternaria leaf spot. The weeds were identified as Thlaspi arvense L., a winter annual commonly referred to as field pennycress, stinkweed, or fanweed depending on geographic location. Isolations from the diseased weed tissue yielded A. brassicicola (2). The numerous conidia occurred in chains of 10 or more, ranged in size from 14 to 53 μm in length, were 5 to 18 μm wide, contained from 1 to 6 transverse septa with rare longitudinal septa, and were olivaceous in color. An apical beak was absent. On potato dextrose agar (PDA) the colony was dark olive-green to black in color and velvety. Seed was collected from the T. arvense plannts in the spring of 1997. One hundred seeds were placed in petri plates containing PDA amended with 0.01% of chloramphenicol and streptomycin sulfate. A. brassicicola was not isolated from the seeds. A different area of the field was planted to cabbage in 1997 and the cruciferous weeds were allowed to grow. The 1997 population of T. arvense consisted of plants from the previous season that flowered early and plants from seeds that germinated late in the season but did not flower. A. brassicicola was isolated from nonflowering weeds in September and from flowering weeds in October. Nonflowering plants were removed from the field in November, planted in pots, and placed in the greenhouse to induce flowering. Identity of both plant populations was confirmed as T. arvense (Warren Lamboy, Cornell University, Geneva, NY). Pathogencity of A. brassicicola isolates from T. arvense was demonstrated on cabbage and T. arvense by following Koch's postulates. Conidia (10) from a 5-day-old culture isolated from T. arvense grown on PDA were atomized onto field pennycress and cabbage plants with a Preval sprayer. The plants were enclosed in plastic bags and put under lathe shading in the greenhouse. The pathogen was reisolated from symptomatic tissue of both plants after 5 days. This weed could serve as a potential source of A. brassicicola inoculum because it is not controlled by herbicides used in crucifer production systems. Alternaria raphani has been reported on T. arvense in Canada (1). This is believed to be the first report of A. brassicicola on T. arvense. References: (1) K. Mortensen et al. Can. Plant Dis. Surv. 73:129, 1993. (2) P. Neergaard. 1945. Danish Species of Alternaria and Stemphylium. Oxford University Press, London. pp. 137-138.
1996年8月1日，在纽约州日内瓦一块甘蓝地里生长的十字花科杂草上发现了叶斑病。杂草上的叶斑颜色为深灰色至黑色，大小不一，从针尖大小到直径1毫米不等。甘蓝（Brassica oleracea L. var. capitata L.）感染了甘蓝链格孢（Alternaria brassicicola (Schwein.) Wiltshire），这是甘蓝链格孢叶斑病的病原菌。这些杂草被鉴定为田野碎米荠（Thlaspi arvense L.），这是一种越年生植物，根据地理位置不同，通常被称为野荠菜、臭草或扇叶荠。从患病杂草组织中分离出了甘蓝链格孢（2）。大量分生孢子呈10个或更多个的链状排列，长度在14至53微米之间，宽度为5至18微米，有1至6个横向隔膜，很少有纵向隔膜，颜色为橄榄色。没有顶端喙。在马铃薯葡萄糖琼脂（PDA）上，菌落颜色为深橄榄绿色至黑色，呈天鹅绒状。1997年春天从田野碎米荠植株上采集了种子。将100粒种子放在含有添加了0.01%氯霉素和硫酸链霉素的PDA的培养皿中。未从种子中分离出甘蓝链格孢。1997年在该田地的不同区域种植了甘蓝，并让十字花科杂草生长。1997年的田野碎米荠种群包括上一季早开花的植株以及本季晚发芽但未开花的种子长成的植株。9月从不开花的杂草中分离出了甘蓝链格孢，10月从开花的杂草中分离出了该病菌。11月将不开花的植株从田间移除，种植在花盆中，并放置在温室中诱导开花。这两个植株种群均被确认为田野碎米荠（沃伦·兰博伊，康奈尔大学，纽约州日内瓦）。通过遵循科赫法则，证明了从田野碎米荠分离出的甘蓝链格孢菌株对甘蓝和田野碎米荠具有致病性。用Preval喷雾器将从在PDA上生长的田野碎米荠分离出的5日龄培养物中的分生孢子（10个）喷到野荠菜和甘蓝植株上。将植株用塑料袋套住，并放在温室中的车床遮荫下。5天后从两株植物的症状组织中重新分离出了病原菌。这种杂草可能是甘蓝链格孢接种体的潜在来源，因为它不受十字花科作物生产系统中使用的除草剂控制。在加拿大，田野碎米荠上曾报道过萝卜链格孢（Alternaria raphani）（1）。据信这是关于田野碎米荠上甘蓝链格孢的首次报道。参考文献：（1）K. 莫滕森等人。《加拿大植物病害调查》73:129，1993年。（2）P. 尼尔加德。1945年。丹麦的链格孢属和匍柄霉属物种。牛津大学出版社，伦敦。第137 - 138页。
