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

Abstract

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.

Infection of Vitis vinifera (cv Chardonnay) Inflorescences by Colletotrichum acutatum and Greeneria uvicola

“…Our results confirm the susceptibility of V. vinifera cv Chardonnay inflorescences to infection by G. uvicola and C. acutatum (Steel et al. ). Under the conditions of our study at 25°C, C. acutatum infection commenced as little as 2 h postinoculation, while infection of flowers by G. uvicola did not commence until 12 h postinoculation.…”

“…While these bunch rot pathogens predominately attack mature berries, evidence is gathered to indicate that grapevine flowers are also susceptible to infection (Steel et al. ). Provided clusters do not abort; it is possible that flower infections may remain latent after fruit set and resume growth after the onset of grape berry ripening (veraison) as for grey mould of grapes caused by Botrytis cinerea (Keller et al.…”

Modeling the Effects of the Environment and the Host Plant on the Ripe Rot of Grapes, Caused by the Colletotrichum Species

“…The estimates and standard errors of the equation parameters were 27.686 ± 1.843, 0.520 ± 0.106, and 1.453 ± 1.100. Equation (4) was developed by using the data of Steel et al [17] and Yun and Park [28], with R 2 = 0.876 (see Figure S3 in the Supplementary Materials). The second equation concerns wetness duration: f (WD) = 1 − exp(− ((0.065WD) 3.321 )) (5) where WD is the duration of the wet period (i.e., the number of hours with uninterrupted leaf wetness or interrupted by a maximum of 3 h).…”

“…In the next season, acervuli produce abundant conidia splash-dispersed to healthy tissues and serve as inoculum for repeated primary infection cycles. Conidia germinate, produce appressoria, and penetrate the cuticle of berries, which are susceptible from flowering to ripening [4,17,32]. Infected berries, however, do not show symptoms until ripening, i.e., the infection remains quiescent until véraison or later [18,33].…”

“…The control of ripe rot relies mainly on the repeated use of fungicides throughout the growing season. Lime sulfur is applied before bud break to reduce the overwintered inoculum [6]; strobilurin fungicides are recommended at flowering [17], and protective broad-spectrum fungicides such as captafol, captan, maneb, or benomyl are repeatedly applied from "small green fruits" to "fruit turning bronze" at 2-week intervals [18]. Such an intensive fungicide calendar is not economically or ecologically sound and may result in needless sprays.…”