Ali S, Francl L J, Iram S, Ahmad I
Department of Plant Pathology, North Dakota State University, Fargo 58105.
Crop Diseases Research Institute, Islamabad, Pakistan.
Plant Dis. 2001 Sep;85(9):1031. doi: 10.1094/PDIS.2001.85.9.1031B.
Tan spot is caused by Pyrenophora tritici-repentis and is an economically important foliar disease of wheat worldwide. The fungus produces two types of symptoms, necrosis and chlorosis, on susceptible wheat cultivars. Isolates have been grouped into five races based on their ability to induce necrosis (nec+) and chlorosis (chl+) on appropriate wheat differentials (1,2). During March 2000, foliar diseases of wheat were surveyed in major wheat-growing areas of the Punjab Province of Pakistan. Tan spot was observed at 13 locations in the province. Diseased leaf samples were collected from all 13 locations to satisfy Koch's postulates. Isolations were made by placing 2-cm-long diseased leaf pieces in petri dishes with three layers of dampened Whatman No. 1 filter paper. The leaf pieces were incubated under an alternating cycle of 24 h of light at 21°C and 24 h of dark at 16°C. A fungus that produced erect, single dark yellow-brown conidiophores with single light yellow-brown conidia was recovered from all the samples and identified as Drechslera tritici-repentis, the anamorph of Pyrenophora tritici-repentis. Single spores were transferred on V8 potato dextrose agar for further study. Seven single spore isolates recovered from the samples were imported through APHIS and tested for pathogenicity and race structure in a growth chamber at North Dakota State University. Two-week-old seedlings of wheat differentials were inoculated individually with a spore suspension of each isolate, and consistent results were found in four replicated experiments. Four of seven isolates were identified as race 1 (nec+chl+), whereas, three isolates did not correspond to any of the currently identified five races. For all these isolates, one of the differentials (Katepwa), which exhibits necrosis, chlorosis, or neither symptom to the five described races, showed both necrosis and chlorosis. This is the first report of the occurrence of tan spot of wheat in Pakistan. The widespread presence of tan spot in the region is a potential threat to wheat production. References: (1) De Wolf et al. Can. J. Plant Pathol. 20:349, 1998. (2). Lamari et al. Can. J. Plant Pathol. 17:312, 1995.
黄斑病由小麦黄斑病菌引起，是一种在全球范围内对小麦经济影响重大的叶部病害。该真菌在感病小麦品种上会产生两种症状，即坏死和褪绿。根据其在合适的小麦鉴别品种上诱导坏死（nec+）和褪绿（chl+）的能力，分离菌株已被分为五个生理小种（1,2）。2000年3月，对巴基斯坦旁遮普省主要小麦种植区的小麦叶部病害进行了调查。在该省的13个地点发现了黄斑病。从所有13个地点采集了病叶样本以满足柯赫氏法则验证。将2厘米长的病叶片段放置在装有三层湿润的沃特曼1号滤纸的培养皿中进行分离培养。叶段在21°C光照24小时和16°C黑暗24小时的交替循环条件下培养。从所有样本中分离出一种产生直立、单个深黄褐色分生孢子梗且带有单个浅黄色褐色分生孢子的真菌，并鉴定为小麦黄斑病菌的无性型——德氏霉属小麦黄斑病菌。单个孢子被转移到V8马铃薯葡萄糖琼脂上进行进一步研究。从样本中获得的7个单孢分离株通过美国动植物卫生检验局进口，并在北达科他州立大学的生长室中进行致病性和生理小种结构测试。用每个分离株的孢子悬浮液分别接种两周龄的小麦鉴别品种幼苗，在四个重复实验中得到了一致的结果。7个分离株中有4个被鉴定为生理小种1（nec+chl+），而另外3个分离株与目前已鉴定的五个生理小种中的任何一个都不对应。对于所有这些分离株，其中一个鉴别品种（Katepwa），对所描述五个生理小种表现出坏死、褪绿或无任何症状，对这些分离株却同时表现出坏死和褪绿。这是巴基斯坦小麦黄斑病发生情况的首次报道。该病害在该地区的广泛存在对小麦生产构成了潜在威胁。参考文献：(1) De Wolf等人，《加拿大植物病理学杂志》20:349，1998年。(2) Lamari等人，《加拿大植物病理学杂志》17:312，1995年。
