Survival and viability of ascospores of Erysiphe necator in Austrian vineyards

Abstract

Grape powdery mildew caused by Erysiphe necator is a limiting factor in grape production. In order to develop effective management strategies, the factors influencing the survival of the fungus need to be identified and characterized accordingly. For this purpose, we focused on the effect of weather conditions during overwintering on the survival and viability of ascospores. In spring 2017 and 2018, grape leaf litter and bark samples were collected and examined to determine the density of chasmothecia and the viability of ascospores in various Austrian vine growing regions. There were obvious differences in the amounts of chasmothecia between both years and all examined vineyards. Lower quantities of chasmothecia were detected on the exfoliating bark compared to leaf litter, with up to 37% of chasmothecia containing viable ascospores. In comparison, chasmothecia from leaf litter showed a lower viability (up to 5%). The number of viable ascospores per head of vine ranged from 0 to 351 and from 0 to 251 in 2017 and 2018, respectively, and showed partly a strong variation within one location in both years. The infectivity of ascospores on detached leaves was confirmed. In a survival experiment, chasmothecia, when incubated at 7 °C, released more viable ascospores than chasmothecia incubated at 17 °C. After an incubation period of 30 weeks, only chasmothecia stored at the lower temperature contained viable ascospores. However, the mean temperature differences of 0.1 to 1.2 °C during the period of formation of chasmothecia to bud break in both years and six investigated areas did not explain differences in the viability of the ascospores. Differences in vineyard management seem to be of particular importance here.

Chitosan-Based Bioactive Formulations for the Control of Powdery Mildew in Viticulture

“…secondary metabolites. Chasmothecia isolated and preserved in suitable conditions (cool, dry place with a not very high temperature of around 15-18 • C) lose viability, with some authors describing up to 50% loss of viability after 16 weeks of preservation at 17 • C [40]. This could explain why the control treatment showed a percentage of viability in the ascospores used of 69%.…”

Efficiency of inorganic fungicides against the formation of Erysiphe necator chasmothecia in vineyards

“…Globally, chasmothecia are the most important source of inoculum 2,4,6–11 . Their formation starts on grapevine tissue at the end of summer.…”

“…Chasmothecia are dispersed by rain to the exfoliating bark of vines and onto the soil, 12 or they remain on the leaves in the absence of rain 6 . In most wine‐growing regions, only chasmothecia overwintering on the exfoliating bark contain a high number of viable ascospores after bud break 4,12 . Furthermore, chasmothecia can only release ascospores after a physiological, temperature‐influenced maturation process 14,15 .…”

“…Burrill), can perennate either as chasmothecia-containing ascospores 2 or latently as mycelia in the buds of the vines. 3 Primary infections of the leaves in spring can therefore be caused by ascospores from chasmothecia 2,4 or conidia from shoots coated with mycelia originating in infected buds. 5 Globally, chasmothecia are the most important source of inoculum.…”

“…5 Globally, chasmothecia are the most important source of inoculum. 2,4,[6][7][8][9][10][11] Their formation starts on grapevine tissue at the end of summer. During the morphological maturation process, 12 they change their colour through melanisation, starting from white after initiation, to yellow, then brown, finally appearing black.…”