First Report of the Association of Myriogenospora atramentosa with the Plant Genus Hemarthria

Myriogenospora atramentosa is an epibiont fungus that produces black, linear stromata on the leaves of warm-season grasses including the genera Paspalum and Andropogon (Glenn et al. 1998). Infection of a grass by this fungus can lead to a disease called “tangletop,” in which multiple leaves are tangled together by the fungal biomass (Glenn et al. 1998). M. atramentosa infections can also cause various degrees of host plant sterility (Glenn et al. 1998). Because M. atramentosa is in the family Clavicipitaceae containing several ergot alkaloid-producing fungi, its mycotoxin production and the potential risk to cattle health are of concern (Glenn et al. 1998).

Originally from southern Africa, limpograss (Hemarthria altissima) is a warm-season perennial grass that plays a key role in the cattle industry of the southeastern United States (Wallau et al. 2015). Compared with other warm-season grasses, limpograss is better adapted to poorly drained soil, more resistant to cold, and has greater digestibility over maturity, making it a good option for stockpiled forage (Kalmbacher et al. 1998; Wallau et al. 2015). As a result of these desired traits, the planted area of limpograss has expanded in Florida in the past few decades, covering over an estimated 200,000 ha (Wallau et al. 2015). Because limpograss is increasing in popularity as an improved forage species, understanding any potential plant-pathogen interaction and its effect on the forage quality is essential.

Limpograss plants with tangletop signs and symptoms were collected in October 2018 from Osceola County, Florida, U.S.A. The infected, living grasses were retained in the greenhouse of North Florida Research and Education Center at Quincy, Florida. A dried specimen taken from the limpograss cultivar Floralta was deposited in the University of Florida Herbarium (accession FLAS-F-63888). Polymerase chain reaction was conducted targeting the nuclear ribosomal internal transcribed spacer (ITS) and large subunit (LSU) D1 regions (primers ITS1F and LR3) following U’Ren et al. (2010). Sanger sequencing was conducted, and the obtained sequences were submitted to National Center for Biotechnology Information (NCBI) GenBank (ITS, MK953716; LSU, MK953717). To compare the obtained sequences with sequences in the public database, Basic Local Alignment Search Tool (BLAST) was performed in the NCBI portal (accessed May 2019).

M. atramentosa was confirmed to be associated with limpograss cultivar Floralta (Fig. 1). A similar tangletop morphology was also reported by photographs in the field for the cultivars Gitbuck and Kenhy, but these records require further microscopic and molecular confirmation. The infected plants of Floralta showed tangletop symptoms at an earlier stage of development (Fig. 2A). When the leaf of Floralta expanded and unfolded, the black, linear stroma appeared along the midrib of the leaf (Fig. 2A). The investigated asci produced on Floralta were unitunicate, and fusiform (Fig. 2B). Ascospores were at first cylindrical and later on broke into fusoid part-spores (Fig. 2C). Overall, the morphological characteristics of the teleomorph reported herein match previous descriptions of M. atramentosa (Glenn et al. 1998). However, M. atramentosa on limpograss sometimes merges several leaves consecutively along the stem, causing fungal signs that look like black line braids (Figs. 1C and 2A).

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The top BLAST hits of ITS and LSU belonged to sequences previously identified as M. atramentosa and showed little to no divergence from the existing M. atramentosa sequences (Table 1). Although a wide range of host species have been reported for M. atramentosa (Glenn et al. 1998), all molecular sequences publicly available have been generated from samples collected in the eastern United States (Table 1). Research with broader sampling schemes is required to understand the global geographic distribution and genetic diversity of M. atramentosa. The M. atramentosa–H. altissima association has not been reported from ranches located in north Florida, so efforts should be made to carefully examine pastures of limpograss in that area in the future to ascertain the northern limit of the disease’s occurrence.

TABLE 1 Top BLAST results of ITS and LSU sequences of Myriogenospora atramentosa on limpograss obtained in this study^a

ITS				LSU
Sequence similarity (%)	GenBank accession	Host	Location	Sequence similarity (%)	GenBank accession	Host	Location
100	KM456196	Pennisetum alopecuroides, Miscanthus sinensis	NC, U.S.A.	100	AY489733	Andropogon virginicus	GA, U.S.A.
100	U57407	Andropogon virginicus	GA, U.S.A.	100	U57084	Andropogon sp.	GA, U.S.A.
100	JN049835	NA	NA	98.9	U68125	Paspalum distichum	NA
96.4	U57406	Erianthus contortus	GA, U.S.A.

^a Host information was derived from NCBI references. All BLAST hits shown were identified as M. atramentosa by the submitters. NA = not available.

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M. atramentosa was considered to be restricted to plants in the new world (Glenn et al. 1998) (Fig. 3). However, H. altissima has a worldwide distribution (Fig. 3) and is also used as forage in Asia, South America, and Oceania (Xue et al. 2017). M. atramentosa is reported to be associated with the plant genus Hemarthria for the first time, through morphological and molecular investigations. Because of the increasing human usage, animal consumption, and global distribution of H. altissima, understanding its codistribution with M. atramentosa and the potential mycotoxin content is critical to protect plants and animals.

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