First Report of Fusarium acuminatum Causing Dianthus chinensis root rot and foliage blight in China.

Dianthus chinensis is a popular ornamental plant that is widely cultivated in China. In May 2020, a disease was found at several landscape sites in Xuanwu District, Nanjing, China, causing symptoms of foliage blight and root discoloration on approximately 52% of one-year old D. chinensis plants. To recover the causal pathogen, samples of infected roots and leaves were cut into 5×5 mm2 pieces, surface-disinfected in 75% ethanol for 30 sec, followed by 1% NaClO for 90 sec, rinsed with sterile water three times and placed on potato dextrose agar (PDA) with 0.1 mg/mL of ampicillin at 25 ⁰C. Hyphae growing on PDA were visible from both root and leaf tissues after three days. Individual hyphal tips were transferred to new PDA plates to obtain pure isolates. Three representative isolates were deposited in the China Forestry Culture Collection Center (CFCC 57545,57546, 57547). The hyphae grew radially, densely, and the aerial hyphae were velvety, white, yellow-white, or pink-white. Representative isolate Facu-DCY5 produced three types of conidia (microconidia, macroconidia, and chlamydospores). Macroconidia were sickle-shaped, measuring 25.7-55.4 µm × 3.2-4.6 µm (n=50). Microconidia were numerous, oval or kidney-shaped, measuring 6.8-11.9 µm × 3.5-4.8 µm (n=50). Conidia produced in the aerial mycelium were 16-34 × 2.2-5.3 µm (n=50). The ITS region, TEF1, calmodulin (CMDA), and RNA polymerase II second largest subunit (RPB2) were amplified with primers ITS1/ITS4, EF1/EF2, CL1/CL2A and 5F2/7CR , respectively and sequenced at Sangon Biotech (Nanjing, China). The ITS sequence of isolate Facu-DCY5 (GenBank No. ON307073.1) was identical to HQ165938.1, ON306850.1, OM964482.1. TEF1 (ON331997.1) was identical to LC546967.1, HQ165866.1, MZ158155.1. CMDA (ON331996.1) was identical to HQ412345.1, MZ921595.1 and MZ921597.1. RPB2 (ON331995.1) was identical to MZ997370.1. Maximum parsimony and maximum likelihood phylogenies of the Facu-DCY5 multilocus sequence data and those of several species within the F. tricinctum species complex identified the isolate from D. chinensis as F. acuminatum . Pathogenicity tests were performed using a conidial suspension (104 conidia/mL). Each plant (approx. 0.3 m in -height) was inoculated with 1 mL of the conidial suspension by mixing it into the potting soil (500 g). Control plants were treated with sterile distilled water. All inoculated plants (n=9) in three repeats of the assay exhibited foliage blight and root rot after 15 days, whereas all control plants (n=9) remained asymptomatic. Fusarium isolates with identical morphological features and molecular marker sequences to those of Facu-DCY5 were recovered from foliage blight and root tissues of all the inoculated plants. In China, F. acuminatum has been reported as a pathogen of Cucurbita maxima, Actinidia arguta, Polygonatum odoratumand Schisandra chinensis. This is the first report of F. acuminatum on D. chinensis in China. Considering the importance of D. chinensis to both ornamental nurseries and landscaping industries, we recommend that diseased plants be removed to prevent the spread of F. acuminatum, and that identification of the infecting isolates from D. chinensis at other sites and landscape locations be performed.