First Report of Fusarium solani Causing Soft Rot on Sansevieria cylindrica in the Republic of Korea

Abstract

Sansevieria cylindrica Bojer ex Hook. (cylindrical snake plant) is one of the most popular ornamental succulent plants in the Republic of Korea. It is highly tolerant to various stress conditions, and therefore, easy to take care. Rigid and flat leaves come out from the basal part of the plant become cylindrical in a mature plant, and cuttings of each cylindrical leaf are potted and sold on the market. In March 2019, we got four individual plants from a floriculture farm (37°41'36.0"N; 126°44'19.6"E) and observed soft rot symptom. Symptomatic tissues were cut to approximately 1 cm3, surface-sterilized with 1% NaOCl, and placed on potato dextrose agar (PDA) at 25 ℃ for 4 days. Two fungal isolates had creamy white colony with rare aerial mycelium on PDA. Macroconidia were 4-5-septate, sickle-shaped, gently curved, measuring 28.1 to 49.1 × 3.7 to 5.8 µm. Microconidia, consisting of only one or two cells, were oval or reniform shaped and had various dimensions of 3.0 to 19.8 × 1.4 to 5.0 µm. Based on the morphological characters, the isolates were identified as Fusarium sp.(Leslie et al., 2008). Genomic DNA was extracted from a single-spore isolate (JYR6) and the internal transcribed spacer (ITS) region of the ribosomal DNA (rDNA) and transcription elongation factor 1-α (TEF1) were amplified and sequenced using primer pairs ITS1/ITS4 and EF1/EF2, respectively (White et al., 1990, Karlsson et al., 2016). The ITS and TEF1 sequences of JYR6 were deposited in NCBI GenBank (MT261780 and MT274305, respectively). BLASTn analysis of the ITS sequence of JYR6 revealed 99 to 100% identities with those of F. solani isolates (KX379166 and KP269017), and the TEF1 sequence also showed 99 to 100% identities with those of F. solani isolates (JF740787 and KM580555). To fulfill Koch’s postulate, cuttings of S. cylindrica were inoculated with JYR6. Fungal isolates were incubated in 50 ml carboxymethyl cellulose (CMC) medium on a rotary shaker (200 rpm) at 25 ℃ for 5 days to produce conidia. The rhizome including roots of healthy plants were cut and dipped into sterilized water or conidial suspension (5 × 107 conidia/ml) for an hour, and then replanted in sterilized soil. After 9 days post inoculation, infected plants started showing initial symptoms of rot from the cut-region and spread upward when the mock control plants remained healthy. Symptomatic regions looked like water-soaked and were squashy. After infection, the color of vascular bundle changed from white to reddish brown as those of intrinsic infected plants. Fungal strains re-isolated from symptomatic tissues were revealed to be JYR6 based on both ITS and TEF1 sequencing analyses. To our knowledge, this is the first report that F. solani causes soft rot on S. cylindrica in the Republic of Korea. This report expanded the host range of F. solani and offered a case of house plant disease.