Location: Foreign Disease-Weed Science
Title: First Report of Leaf Necrosis on Microstegium vimineum caused by Bipolaris microstegii in Maryland Authors
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 30, 2013
Publication Date: January 8, 2014
Citation: Bruckart, W.L., Eskandari, F., Lane, W. 2014. First Report of Leaf Necrosis on Microstegium vimineum caused by Bipolaris microstegii in Maryland. Plant Disease. doi:org/10.1094/PDIS-11-13-1122PDN. Interpretive Summary: A leaf spot disease was discovered in Frederick, Maryland, on the plant commonly known as Japanese stiltgrass. This grass is invasive, often becoming the only plant growing in lawns, parks, and other natural areas. Because there is so much of this grass, the ecosystem is changed. Deer, for example, have difficulty finding native plants to eat. The disease is caused by a fungus known as Bipolaris microstegii, based on our examination and tests. It is similar to samples of the fungus from West Virginia, including the original isolate. Tests included microscopic examination of the fungus, inoculation of plants, and comparison of DNA with that of other isolates. This is the first report and clear identification of this disease in Maryland, although a similar leaf spot was found in Maryland in 2009. The isolate causes a lot of damage to some, but not all inoculated Japanese stiltgrass in greenhouse tests, and additional studies are in progress to clarify the importance of this disease, not only in Maryland, but in the United States.
Technical Abstract: Diseased Japanese stiltgrass (JSG, M. vimineum) was discovered in August 2012 at a residence on Indian Springs Road, Frederick, MD (Lat., Long.: 39.46747, -77.46106). The infestation was small, within an area of 2 x 4 m, and shaded because it was on the north side of a structure and otherwise surrounded by trees. JSG occurred in larger monoculture stands at sunny locations within 6 – 10 m that only had a few, small necrotic spots. Diseased plants had leaves with brown, often large, elliptical, necrotic spots, generally surrounded by a diffuse chlorotic margin, and the larger lesions with tan centers. Diseased plants were smaller in stature and less thrifty than non-symptomatic plants nearby. Symptoms were similar to those on JSG reported by Kleczewski and Flory. Field samples of diseased leaves in moist chambers at room temperature and lighting produced dematiaceous conidiophores and conidia typical of Bipolaris within 2 days. Cultures growing on Modified Potato Dextrose Agar (broth from 140 g each of potatoes and carrots and 20 g agar in 1 L water), were grey, velutinous or tomentose, and had clumps of short aerial hyphae on the upper surface. Three inoculations, with a minimum of 5 plants/replication grown from soil collected at the site of discovery, resulted in brown or dark tan necrotic irregular, often linear, spots with entire margins. Bipolaris was recovered from all symptomatic plant samples incubated in moist chambers. Conidia were produced sympodially on dematiaceous conidiophores, often with clusters of 2 – 3 spores at the terminis. Spores were medium- to dark-brown, straight or slightly curved, nearly fusiform with obtuse apices, typically with 8 – 10 distoseptate cells, and they measured (mean ± ci, P = 0.05; n = 100) 74.8 µm ± 2.3 x 16.4 µm ± 0.3, and Q = 4.6 ± 0.1. A sequence of the ITS1-5.8S-ITS2 region of DNA, extracted using a DNeasy Plant Mini Kit (QIAGEN), was found 100% identical (with no gaps) to that of B. microstegii isolate AR4840 from M. vimineum (BPI 883727; GenBank Accession Nos. JX089579, JX089575), using BLAST. On the basis of fungal characteristics, molecular information, and host plant, the causal agent of this disease has been determined to be B. microstegii. This isolate, FDWSRU 12-049, has been deposited in the US National Fungus Collection (BPI 892680) and sequence information is in GenBank, Accession No. KF150215. This is the first confirmed identification of B. microstegii on Japanese Stiltgrass in Maryland. A Bipolaris leaf spot was found in Howard and Prince Georges Counties, MD, in 2009, but they were not formally characterized (K. Rane, Univ. Maryland; personal communication).