First Report of Honeysuckle Leaf Blight on Amur Honeysuckle (Lonicera maackii) Caused by Insolibasidium deformans in Tennessee

Honeysuckle leaf blight, incited by Insolibasidium deformans (C. J. Gould) Oberw. & Bandoni, infects at least 18 Lonicera species and Symphoricarpos albus (L.) Blake (Caprifoliaceae), and has been reported across the northeastern and north-central United States and Canada (Gould 1945; Riffle and Watkins 1986). In early May 2018, foliar chlorosis and necrosis consistent with symptoms of I. deformans were observed on Amur honeysuckle, L. maackii (Rupr.) Herder on recently matured regrowth foliage in Oak Ridge, TN, arboretum borders. Beneath chlorotic lesions and often adjacent to necrotic leaf tissues, a thin, white layer of basidia and basidiospores was visible mostly on abaxial leaf surfaces. The hyaline, uninucleate, slightly curved, and cylindrical basidiospores possess an apiculus on the end, from which they arise from curved, transversely septate basidia. Basidiospores measured 10.2 µm (8.3 to 12.2 µm) × 6.2 µm (4.5 to 7.5 µm) (n = 30). Conidia (Glomopsis sp.) may be produced as resting spores later in the season but were not observed. Observed fungal morphology closely agrees with the description for I. deformans (Gould 1945; Oberwinkler and Bandoni 1984). Lesions were excised and total gDNA isolated and amplified with ITS1 and ITS4, and the amplicons of the plant and fungus were processed according to the method of Trigiano et al. (2016) for sequencing. The sequence for I. deformans was entered into GenBank (MH790966) and was 100% identical to GenBank I. deformans accession GU291277. The sequence for L. maackii, entered into GenBank as MH790967, was ≥99% identical to GenBank accession EU240695. On 29 June 2018, inoculations were made using infected Amur honeysuckle leaves held against newly emerged foliage with a hair clip on five propagated, irrigated, disease-free L. maackii plants. Nonsymptomatic leaves from extra honeysuckle plants were attached to leaves on an additional five control plants. Plants were held at 75 ± 10°F (24 ± 5.5°C) with a 12-h light/dark photoperiod and kept in fiber sleeves for 3 days to maintain humidity, with clips and infected leaf tissues removed after the first 12 h. Chlorosis, visible on both sides of inoculated leaves, first appeared 19 days after inoculation, and necrotic leaf tissues were present 6 days later. Honeysuckle leaf blight signs and symptoms identical to those of the original disease materials were observed on five of five inoculated L. maackii plants. All controls remained disease-free. After molecular confirmation from inoculated host foliage, we conclude that I. deformans was the causal pathogen of honeysuckle leaf blight on L. maackii in Tennessee. This observation is the southernmost occurrence reported for I. deformans, and consistent symptomology was also observed in early June 2018 on L. maackii in Chattanooga, TN. In contrast with a recent report from northern Kentucky (Boyce 2018), there is little evidence that infection has led to appreciable levels of shoot death of L. maackii shrubs in eastern Tennessee. These nonnative invasive plants may serve as bridge species or a reservoir for primary inoculum to infect other susceptible honeysuckle species.