FIRST REPORT OF PEPPER SPOT DISEASE OF LYCHEE CAUSED BY COLLETOTRICHUM SIAMENSE IN TAIWAN

In 2013, fruits and leaves of Litchi chinensis [No Mai Tsz (73-S-20)] with symptoms of pepper spot (Cooke and Coates, 2002) were collected from Yunlin county in Taiwan. Diseased leaf tissue was surface-sterilized with 70% ethanol and placed on acidified potato dextrose agar (APDA). A single spore isolate (C-1001) with aerial white mycelium that turned gray at 25°C and a 12 h photoperiod produced salmon conidial masses after 10 days. Conidia were hyaline, aseptate, cylindrical, 14.3 (12.77-15.38) x 4.9 (3.95-5.56) µm in size. For further identification, partial sequences of actin (ACT), calmodulin (CAL), chitin synthase (CHS-1), glyceraldehye-3-phosphate dehydrogenase (GAPDH), and ribosomal internal transcribed spacer (ITS) (Weir et al., 2012) were generated and deposited in GenBank (accession Nos. MF098594, MF135496, MF098596, MF098598 and MF135494, respectively). Baysian inference analysis using multilocus alignment with the deposited sequences placed the isolate (C-1001) in the same clade with the ex-type of C. siamense (ICMP 18578) (Weir et al., 2012). Based on cultural characteristics, conidial morphology (Sutton, 1992) and phylogenetic analysis, the fungus was identified as Colletotrichum siamense (Penz.) Penz. & Sacc. Pathogenicity tests were conducted in the field. Young leaves of lychee cv. 'No Mai Tsz (73-S-20)' were inoculated using a conidial suspension (1.5 x 106 conidia/ml) and covered with moist plastic bags for 48 h. Dark lesions of the pepper spot disease 19 developed on leaves 4 weeks after inoculation. C. siamense was reisolated from the inoculated leaves. To our knowledge, this is the first report of C. siamense causing pepper spot disease of lychee in Taiwan.