Lindsay Greer

Detection and monitoring of Greeneria uvicola and Colletotrichum acutatum development on grapevines by real-time PCR

Bitter rot (Greeneria uvicola) and ripe rot (Colletotrichum acutatum, syn. C. simmondsii) occur frequently in subtropical grape-growing regions of Australia, where they cause yield loss and bitter taints in wine. To further advance the epidemiological studies of G. uvicola and C. acutatum and contribute toward their effective management and control, a rapid and reliable species-specific real-time polymerase chain reaction (PCR) method was developed based on the polymorphic portion of the internal transcribed spacer region of the two fungi. It was found that, within 6 to 8 h postinoculation, the assay could detect as little as 20 fg of genomic DNA and 10 conidia for both species. Artificially and naturally infected grape inflorescences and mature berries were analyzed by both conventional plating methods and real-time PCR. Fungal presence was demonstrated on all plant material but development was observed only on mature berries. The results demonstrate that the real-time PCR technique is a highly specific, rapid, and sensitive method that can be used to detect and study the dynamics of G. uvicola and C. acutatum during different stages of infection and on different grape tissues.

Effects of spray adjuvants on grape (Vitis vinifera) berry microflora, epicuticular wax and susceptibility to infection by Botrytis cinerea

Spray adjuvants were tested for their effects on epicuticular wax morphology, grape berry microflora and susceptibility of berries to Botrytis cinerea on Chardonnay, Shiraz and Cabernet Sauvignon cultivars. The four adjuvants used in this trial altered epicuticular wax morphology. Disintegration of the wax platelets was least for the wetter-spreader recommended for sensitive crops, and greatest for the crop oil concentrate and the activator-penetrant. Waxes did not regenerate over the season after treatment with the adjuvants. A cyprodinil/fludioxonil fungicide was effective at controlling B. cinerea infection, but when combined with an adjuvant, was less effective in the three grape cultivars. Irrespective of whether a fungicide was used, adjuvant application resulted in lower yeast and fungal populations on Chardonnay berries. There were no effects of the adjuvants on the microflora of Shiraz and Cabernet Sauvignon berries, except for the crop oil concentrate which resulted in higher bacterial populations on Cabernet Sauvignon berries. We hypothesise that spray adjuvants increased the susceptibility of grape berries to B. cinerea through epicuticular wax alteration and, in some circumstances, through the reduction of the indigenous microflora on the berry surface.

Grapevine inflorescences are susceptible to the bunch rot pathogens, Greeneria uvicola (bitter rot) and Colletotrichum acutatum (ripe rot)

Grapevine inflorescences (cv. Chardonnay) were found to be susceptible to infection by the berry rotting pathogens Colletotrichum acutatum and Greeneria uvicola responsible for ripe rot and bitter rot of grapes respectively. Infection of inflorescences on field-grown grapevines at mid-flowering led to subsequent berry rot at veraison. An application of the strobilurin fungicide Cabrio (active ingredient pyraclostrobin) at flowering reduced the incidence of ripe rot and bitter rot at veraison from 88% to 0% and from 86% to 2%, respectively. The infection of detached inflorescences was influenced by temperature and was greatest at 25–30°C for C. acutatum and 30°C for G. uvicola. Our results demonstrate for the first time that grapevine flowers are susceptible to C. acutatum and G. uvicola and that flower infections have the potential to lead to subsequent rotting of the grape berries. The findings have implications for the management of ripe rot and bitter rot of grapes.