Ripe rot of south-eastern Australian wine grapes is caused by two species of Colletotrichum: C. acutatum and C. gloeosporioides with differences in infection and fungicide sensitivity

Abstract

Background and Aims: Ripe rot of grapes is widespread in subtropical vineyards of south-eastern Australia. We aimed to re-evaluate the causative agent(s), berry susceptibility, fungicide sensitivity and differences in histopathology. Methods and Results: Both Colletotrichum acutatum and C. gloeosporioides were shown to be responsible for ripe rot in three vineyards surveyed in the Hastings Valley, NSW in 2007 and 2009. Observation on detached berries of Vitis vinifera (cv. Cabernet Sauvignon and Chardonnay) revealed that C. acutatum had a faster infection rate than C. gloeosporioides. C. acutatum also formed appressoria and penetrated grape tissue faster than C. gloeosporioides, which produced longer hyphae on the berry surface before penetration. Both C. acutatum and C. gloeosporioides produced acervuli 48 h after inoculation. In contrast, spore germination rates and growth rates on potato dextrose agar were greater for C. gloeosporioides. The two species differed in their sensitivity to the fungicides benomyl, captan and triadimenol. C. acutatum was significantly more sensitive to captan and triadimenol, whereas C. gloeosporioides was more sensitive to benomyl. Conclusions: Both C. acutatum and C. gloeosporioides cause ripe rot of wine grapes in Australia. Subtle differences in the infection process may explain the relative prevalence of the two species. Significance of the Study: This study confirms the involvement of C. acutatum and C. gloeosporioides in ripe rot of grapes in Australia. Knowledge of growth characteristics and fungicide sensitivity of ripe rot pathogens should aid disease management strategies.