Germination and growth of Colletotrichum acutatum and Colletotrichum gloeosporioides isolates from coffee in Papua New Guinea and their pathogenicity to coffee berries

The biology and pathogenicity of Colletotrichum acutatum and C. gloeosporioides isolates from infected coffee berries with anthracnose in Papua New Guinea (PNG) was investigated in vitro and in vivo. Optimum germination in vitro occurred at concentrations of 1 x 10 conidia/mL, while germination was inhibited by 1 x 10 conidia/mL. Optimum germination of C. acutatum and C. gloeosporioides conidia occurred at temperatures between 21-29°C and 25-31°C respectively, after 18-24 h incubation periods, between pH5- pH7 and 100% RH. Maximum growth of C. acutatum occurred at 21°C and C. gloeosporioides at 25-31°C. Conidial germination increased in the presence of free water in both species. Colletotrichum acutatum produced abundant secondary conidia in culture. The process of infection of attached and detached coffee berries by conidia of C. gloeosporioides and C. acutatum was investigated and demonstrated to be equivalent for the two species. The optimum temperatures for conidia germination, appressoria formation and anthracnose development ranged between 25-31°C. Conidia germinated after 3-12 h, appressoria were formed after 6-48 h and anthracnose symptoms appeared 6 days after inoculation. Colletotrichum acutatum infected both non-wounded and wounded green and ripe red berries whereas C. gloeosporioides only infected ripe red non-wounded and wounded berries. This is the first report of C. acutatum as an etiological agent of coffee berry anthracnose