First Report of Anthracnose Caused by Colletotrichum sansevieriae on Sansevieria trifasciata var. laurentii in China

Sansevieria trifasciata var. laurentii (De Wild.) N.E. Brown, commonly known as variegated snake plant or variegated mother-in-law's tongue, is a popular landscape and house plant. In September and October 2019, the obvious leaf spot symptoms were observed on the plants in a 0.2 hm2 of nursery in Qingdao city of China with incidence of 55%. The disease usually starts from the tip or edge of the leaf, initially have slightly water-soaked semi-circular or round brown lesions, which gradually expanded and coalesced into irregular shapes about 3-8 cm in diameter. Grayish brown sunken spots with dark margins that evolve into concentric rings of acervuli which were characteristic of anthracnose, and orange sticky conidial masses were observed under the moist condition. The leaves with typical anthracnose symptoms were collected and deposited in the herbarium of Qingdao agricultural university under accessions no. QDHB074-QDHB087. Subsequently 20 isolates with the same colony and morphological characteristics were obtained from ten diseased leaves by placing surface-sterilized tissue pieces with typical spots on potato dextrose agar (PDA). Colonies are floccose with grayish-white to dark olivaceous gray color, and gray black on the reverse after 14 days at 28°C. Straight conidia [15.0 to 27.5 × 3.5 to 7.0 μm in size (average 18.2 × 6.1 μm) (n = 50)] were cylindrical, aseptate, hyaline, slippery surface, most with one tapering end and the other oval. Setae were black, 185-230 μm in length, with a thin tip and septate in the middle. Appressoria [6.5 to 7.3 × 7.8 to 9.2 μm in size (average 6.8 × 8.1 μm) (n = 15)] were black to dark brown, solitary, spherical with smooth wall. The fungal isolates were identified as Colletotrichum sansevieriae Nakamura (Nakamura et al. 2006), based on the morphological characteristics. To confirm the identification, the internal transcribed spacer (ITS) and calmodulin (CAL) regions of a representative isolate HWL-1016 were amplified by primers ITS1/ITS4 (White et al. 1990) and CMD5/CMD6 (Weir et al. 2012), respectively. The 549 bp ITS (MN922517) and 597 bp CAL (OM994078) sequences had respectively 100% and 99.30% identity with the sequences from holotype species of C. sansevieriae MAFF 239721 (no. NR_152313 and LC180125). Phylogenetic tree based on ITS and CAL sequences respectively or jointly constructed by PAUP4.0 (Swofford 2002) revealed that the fungus in this study clustered with C. sansevieriae isolates (NR_152313, KC790947, HQ433226, JF911349, MN386823). Pathogenicity test of isolate HWL1016 was evaluated on five 3- to 4-month-old potted S. trifasciata var. laurentii under greenhouse conditions (27±2 °C, 16-hr light/8-hr dark photoperiod, 80% relative humidity). Conidial suspension (1×106 conidia/mL) of the isolated fungus from PDA colonies cultured for 15 days and sterile distilled water (as control) were sprayed on pin-pricked surface-sterilized (70% alcohol) leaves of potted plants, respectively. Three replications (three plants) were done for each treatment, and the experiment was repeated twice. The inoculated plants were covered with plastic films for 2 days and obvious water-soaked wounds were observed on the sixth day. After 16 days, the symptoms of the inoculated plants were similar to those in the nursery, with disease incidence reached 100%, while controls remained symptomless. C. sansevieriae was subsequently reisolated from the symptomatic tissues. Anthracnose on S. trifasciata var. laurentii caused by C. sansevieriae has been reported in Australia, Iran, Japan, Malaysia (Kee et al. 2020), South Korea, USA (Talhinhas & Baroncelli 2021), India (Gautam et al. 2012) and Thailand (Li et al. 2020). To our knowledge, this is the first report of C. sansevieriae causing anthracnose on S. trifasciata var. laurentii in China. This study will contribute to guide effective management based on pathogen.