First detection of Colletotrichum siamense causing anthracnose on Alpinia purpurata
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KeywordsEtiology Polyphasic approach Species complex Sunken necrotic Tropical flowers
Alpinia (Alpinia purpurata) flowers with anthracnose symptoms were collected in Alagoas, Brazil, in December 2016. Colletotrichum-like isolates obtained by single-spore culture in potato dextrose agar (PDA) were initially white and later became brown with abundant aerial mycelium. The underside of the colony was uniformly black with a growth rate of 4.3 mm/day. Conidia were 9.88–19.33 × 3.41–5.91 μm (n = 50), straight to cylindrical, aseptate and hyaline, morphological characters consistent with Colletotrichum gloeosporioides (Weir et al. 2012). To confirm the identity of the isolate, partial sequences of the internal transcribed spacer (ITS) of rDNA, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), calmodulin (CAL), chitin synthase (CHS-1) and actin (ACT) genes were amplified and sequenced (GenBank accession Nos. MH122793, MH122792, MH122790, MH122791 and MH122789 respectively). A Bayesian inference phylogenetic tree (Supplementary Fig. S1) was constructed using a combined sequence alignment and Colletotrichum gloeosporioides complex reference sequences, and C. boninense was used as outgroup (Weir et al. 2012). Isolate COUFAL0201 grouped in the C. siamense clade with the ex-type isolate (ICMP 18578). To confirm pathogenicity tests, 30 μl conidial suspension droplets (106 conidia/ml) were deposited on the surfaces of flowers wounded with a sterile needle. Control flowers received sterile water. Typical anthracnose symptoms were observed in all inoculated flowers after 3 to 5 days (Supplementary Fig. S2). Control fruits presented no symptoms. The pathogen was consistently re-isolated from the infected flowers. To our knowledge, this is the first report of C. siamense causing anthracnose on flowers of Alpinia purpurata in the world.