Isolation and identification of pathogen causing anthracnose on Zinnia elegans Jacq. and fungicides screening

To clarify the pathogen of anthracnose on Zinnia elegans Jacq., according to Koch's law, the diseased leaves were collected for the pathogen isolation and pathogenicity testing. After the pathogenicity test, based on their morphologic characteristics, the isolates were proved to be closely related to Colletotrichum species. To further investigated the pathogen, molecular identification based on the phylogenetic analysis of ACT (actin gene), CHS (chitin synthase A gene), GAPDH (glyceraldehyde-3-phosphate dehydrogenase), ITS (ribosomal internal transcribed spacer), SOD2 (manganese-superoxide dismutase), GS (glutamine synthatase), CaM (calmodulin) and TUB2 (beta-tubulin) was conducted and the pathogen was identified to be C. siamense. Furthermore, the antibiotic activity of nine fungicides to this pathogen was tested in vitro and it was found that the EC₅₀ values of trifloxystrobin + tebuconazole 75% water dispersible granule (WG), triflumizole + tebuconazole 35% suspension concentrate (SC), chlorothalonil 75% wettable powder (WP), azoxystrobin 250 g/L SC, prochloraz 50% WP, difenoconazole 10% WG, prothioconazole 10% SC, fluazinam 500 g/L SC and bromothalonil 25% WP were 0.152, 0.407, 2.48, 252, 0.0342, 0.556, 317, 0.00291 and 27.4 mg/L, respectively. Among them, fluazinam 500 g/L SC and prochloraz 50% WP showed the strongest fungicidal activities.