Waxman K D, Bergstrom G C
Department of Plant Pathology and Plant-Microbe Biology, Cornell University, Ithaca, NY 14853-5904.
Plant Dis. 2011 Aug;95(8):1032. doi: 10.1094/PDIS-03-11-0164.
Switchgrass (Panicum virgatum L.) is a perennial grass with significant potential as a biofuel crop. From 2007 to 2010, foliar lesions were observed in new and mature stands of switchgrass in various locations in New York. Lesions were elliptical with purple margins and white necrotic centers, generally <3 cm long, ~1 mm wide, often coalesced, and containing black setae. Upon incubation, symptomatic leaf tissue developed acervuli with masses of salmon-colored spores. The fungus was identified as Colletotrichum nativas Crouch on the basis of typical cultural characteristics and conidial morphology (1). Conidia were one-celled, hyaline, fusiform, and generally falcate. Conidial length averaged 40 μm (22 to 47 μm) and width averaged 5 μm (4 to 7 μm). Compared with other graminicolous species of Colletotrichum, the conidia were larger and varied from straight to irregularly bent. Sequences of the rDNA internal transcribed spacer (ITS) regions of three isolates (Cornell accession and corresponding GenBank Nos.: Cn071NY08 (from a >20-year-old naturalized stand of switchgrass in Steuben County), JF437053; Cn080NY08 (from 'Pathfinder' in Chemung County), JF437054; and Cn101NY09 (from 'Blackwell' in Chemung County), JF437055) exhibited 100% nucleotide identity to the type isolate of C. nativas (GenBank No. GQ919068) collected from switchgrass selection 'Brooklyn' in New Jersey (1). Pathogenicity of the sequenced isolates along with seven other isolates (Cn105NY09 from 'Sunburst' in Tompkins County; Cn107NY09 from 'Trailblazer' in Tompkins County; Cn109NY09 from 'Forestburg' in Tompkins County; Cn111NY09 and Cn112NY09 from 'Shelter' in Tompkins County; and Cn122NY09 and Cn123NY09 from 'Cave-in-Rock' in Genesee County) was evaluated in greenhouse experiments. Seven- to eight-week-old switchgrass plants were inoculated with conidial suspensions (1 × 10 conidia/ml) of C. nativas. Inoculum or sterilized water was sprayed until runoff. Three plants of each of 'Cave-in-Rock' and 'Kanlow' were sprayed per treatment and the experiment was repeated for 3 of the 10 isolates. Inoculated plants were placed in a mist chamber for 48 h before they were returned to the greenhouse and observed for disease development, which occurred within 1 week of inoculation for both cultivars. No symptoms developed on the control plants. Foliar lesions closely resembled those observed in the field. C. nativas was consistently reisolated from symptomatic tissue collected from greenhouse experiments. Switchgrass anthracnose associated with C. graminicola sensu lata has been reported in many U.S. states (2). On the basis of molecular phylogenetics and distinguishing morphological characters, Crouch et al. erected C. navitas as a novel species distinct from C. graminicola sensu stricto, a taxon restricted to the corn anthracnose pathogen (1). C. nativas was first documented on switchgrass in New Jersey (1) and appears to be the same pathogen causing anthracnose of switchgrass in the adjoining state of Pennsylvania (1,3). To our knowledge, this is the first report of C. nativas causing anthracnose of switchgrass in New York. References: (1) J. A. Crouch et al. Mycol. Res. 113:1411, 2009. (2) D. F. Farr and A. Y. Rossman. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/ , May 5, 2011. (3) M. A. Sanderson et al. Agron. J. 100:510, 2008.
柳枝稷（Panicum virgatum L.）是一种多年生草本植物，作为生物燃料作物具有巨大潜力。2007年至2010年期间，在纽约各地新种植和成熟的柳枝稷植株上观察到叶部病斑。病斑呈椭圆形，边缘紫色，中央白色坏死，通常长度小于3厘米，宽度约1毫米，常相互融合，并带有黑色刚毛。在培养后，有症状的叶片组织上产生了带有大量鲑鱼色孢子的分生孢子盘。根据典型的培养特征和分生孢子形态，该真菌被鉴定为本地炭疽菌（Colletotrichum nativas Crouch）(1)。分生孢子单细胞，透明，梭形，通常呈镰刀形。分生孢子长度平均为40μm（22至47μm），宽度平均为5μm（4至7μm）。与炭疽菌属的其他禾本科寄生菌种相比，该分生孢子更大，形态从直形到不规则弯曲不等。三个分离株（康奈尔保藏号及对应的GenBank编号：Cn071NY08（来自斯泰本县一片20多年的归化柳枝稷林），JF437053；Cn080NY08（来自 Chemung县的‘Pathfinder’），JF437054；以及Cn101NY09（来自Chemung县的‘Blackwell’），JF437055）的核糖体DNA内转录间隔区（ITS）序列与从新泽西州柳枝稷选系‘Brooklyn’分离得到的本地炭疽菌模式菌株（GenBank编号：GQ919068）的核苷酸序列一致性为100% (1)。在温室试验中评估了这三个测序分离株以及其他七个分离株（来自汤普金斯县‘Sunburst’的Cn105NY09；来自汤普金斯县‘Trailblazer’的Cn107NY09；来自汤普金斯县‘Forestburg’的Cn109NY09；来自汤普金斯县‘Shelter’的Cn111NY09和Cn112NY09；以及来自杰纳西县‘Cave-in-Rock’的Cn122NY09和Cn123NY09）的致病性。用本地炭疽菌的分生孢子悬浮液（1×10个分生孢子/毫升）接种7至8周龄的柳枝稷植株。喷洒接种物或无菌水直至径流。每个处理对‘Cave-in-Rock’和‘Kanlow’各喷洒三株植株，对10个分离株中的3个重复该试验。接种后的植株先置于喷雾室中48小时，然后放回温室观察病害发展情况，两个品种在接种后1周内均出现病害症状。对照植株未出现症状。叶部病斑与在田间观察到的病斑非常相似。从温室试验中出现症状的组织中始终能重新分离出本地炭疽菌。在美国许多州都报道过与广义禾生炭疽菌（Colletotrichum graminicola sensu lata）相关的柳枝稷炭疽病(2)。基于分子系统发育学和独特的形态特征，Crouch等人将本地炭疽菌确立为一个新物种，与狭义禾生炭疽菌（Colletotrichum graminicola sensu stricto）不同，后者是一种仅限于玉米炭疽病病原菌的分类单元(1)。本地炭疽菌首次在新泽西州的柳枝稷上被记录(1)，并且似乎是在相邻的宾夕法尼亚州导致柳枝稷炭疽病的同一病原菌(1,3)。据我们所知，这是本地炭疽菌在纽约州导致柳枝稷炭疽病的首次报道。参考文献：(1) J. A. Crouch等人，《真菌研究》113:1411，2009年。(2) D. F. Farr和A. Y. Rossman，《真菌数据库》，美国农业部农业研究局系统真菌学和微生物学实验室。检索自http://nt.ars-grin.gov/fungaldatabases/，2011年5月5日。(3) M. A. Sanderson等人，《农业学报》100:510，2008年。
