First Report of Alternaria alternata Causing Brown Spot on Yucca gloriosa in Korea

Yucca gloriosa L. is an evergreen perennial plant valued for its high drought tolerance and distinctive floral morphology (Ding et al. 2019). In April 2025, leaf spot symptoms were observed on Y. gloriosa plants grown in Suncheon Bay National Garden, Jeonnam province, Korea (34°55′39.12″N, 127°30′39.87″E), with a disease incidence of approximately 20-30% based on visual assessment of about 50 plants in the affected area. Initial symptoms appeared as small dark-brown spots that gradually expanded into irregular circular to elliptical lesions with dark brown to black margins and necrotic centers. As disease severity increased, individual lesions coalesced, resulting in extensive leaf necrosis. To isolate the causal pathogen, symptomatic leaf tissues (5 × 5 mm) were excised from lesion margins, surface-sterilized with 70% ethanol and 1% sodium hypochlorite for 1 min each, rinsed twice with sterilized distilled water, and placed on 1.5% water agar. Plates were inoculated at 25°C in the dark for two weeks, after which emerging hyphae were transferred to potato dextrose agar (PDA). Single-spore purification yielded three isolates, designated SYP-1777 to SYP-1779. Colonies on PDA were dark brown at the center and gradually became grayish brown toward the margins after 7 d. Conidia were light brown, ellipsoid to obclavate, with ornamented walls, and possessed 1-6 transverse and 0-3 longitudinal septa, measuring 16.3-55.6 × 4.2-10.6 μm (avg. 33.1 × 7.1 μm, n = 85). The observed morphological features corresponded to those described for species of Alternaria (van der Waals et al. 2011; Woudenberg et al. 2015). For molecular identification, sequences of ITS (GenBank accession nos.: PX830104 to 06), gapdh (PX842544 to 46), tef1 (PX842547 to 49), rpb2 (PX842550 to 52), Alt a1 (PX842553 to 55), endoPG (PX842556 to 58), and OPA10-2 (PX842559 to 61) were obtained from the three isolates. The ITS (574/574 bp), gapdh (593/593 bp), tef1 (268/268 bp), rpb2 (894/894 bp), Alt a1 (482/482 bp), endoPG (454/454 bp), and OPA10-2 (715/715 bp) sequences were each 100% identical to the corresponding genes of the A. alternata type strain CBS 102598 (MT883457, OM824375, ON237474, OP902373, OP654881, MZ835376, and MZ835370, respectively. A maximum likelihood phylogenetic analysis based on the seven concatenated gene sequences placed the isolates within the A. alternata clade. Pathogenicity tests were conducted using isolate SYP-1777 on leaves of 2-year-old yucca plants. A conidial suspension (1 × 10 6 conidia/mL) prepared from 7-day-old cultures was spray-inoculated onto wounded leaf tissues. Inoculated plants were maintained in a humid chamber at 25°C. Brown spot symptoms developed on inoculated leaves within 7 d, whereas control plants remained symptomless. The experiment was performed three times using leaves from two plants. The fungus was re-isolated from symptomatic tissues and identified as A. alternata based on ITS and Alt a1 sequence analysis, thereby fulfilling Koch's postulates. A comprehensive search of the APS Plant Disease Database, CABI Crop Protection Compendium, and available Korean plant disease reports revealed no previous record of A. alternata causing brown spot on Y. gloriosa in Korea. This is the first report of A. alternata on Y. gloriosa in Korea. Similar diseases on this host have been reported in India and China (Pandey 2019; Zhang et al., 2022). This report will help improve the recognition and management of leaf spot disease on Y. gloriosa in ornamental plantings in Korea.