水稻新病害叶鞘黑斑病的病原鉴定

 2011年7月，在湖南省花垣县水稻上发现一种新的病害，症状表现为叶鞘上出现长椭圆形黑斑，病健交界模糊。分离到的4隔孢弯孢霉(HNHY001)经离体和活体人工接种均可产生黑斑;另一种黑孢霉菌株(HNHY002)不引致叶鞘黑斑。从湖南省栽培水稻150份种子样本中共分离到弯孢霉菌株27个，其中4个菌株具有4隔孢子。这4个菌株中1个菌株不产生子座，其余3个均产生分枝子座。经人工接种除不产生子座的外，其余3个菌株均能产生典型的叶鞘黑斑。HNHY001的rDNA-ITS序列(GenBank登录号JQ360963)经BLAST搜索，与之最接近的几个序列为膝曲旋孢腔菌(Cochliobolus geniculatus)及其有丝分裂产孢种—4隔孢弯孢霉。鉴于单独以及与其它4隔孢弯孢霉菌株进行对峙培养均未产生有性阶段，建议根据此菌无性阶段特征即分生孢子较直、4横隔、子座分枝等特征，鉴定为膝曲旋孢腔菌有丝分裂产孢种之一的假弯孢(C.fallax)。水稻叶鞘黑斑病系国内外首次报道。

Identification of the causal agent of a new rice disease sheath black spot

A new sheath disease of rice was found in Huayuan county of Hunan province in July 2011. One isolate (named as HNHY001) with 4|septate conidia was identified as Curvularia, which caused black spots on rice sheaths by artificial inoculation both in vitro and in vivo. The other one identified as Nigrospora sp. (named as HNHY002) did not induce any lesion. In seed detection, 27 Curvularia isolates were obtained from the 150 rice seed sets in Hunan province. Among those, four isolates were found to contain 4|septate conidia, one of which could not produce branchy stroma and cause disease in an artificial inoculation test. However, the rest 3 isolates caused the typical sheath black spot symptoms. The results of BLAST analysis showed that the rDNA|ITS sequence (JQ360963) of HNHY001 mostly resembled to that of Cochliobolus geniculatus and its mitosporatic 4|septate conidial Curvularia spp.. Considering the fact that the sexual stage of HNHY001 during confrontation cultures with other 4|septate conidial Curvularia isolates were not observed, we therefore regarded the isolate HNHY001 as Curvularia fallax, one of C. geniculatus mitosporatic Curvularia spp. based on the asexual stage characteristics, i.e., slightly straight 4|septate conidium and branchy stromata. This is the first report of rice sheath black spot disease in the world.