Potential and actual ascospore release of Erysiphe necator chasmothecia in Austria

S Steinkellner,M Redl,B Spangl,L Sitavanc

doi:10.1007/s41348-020-00376-0

S Steinkellner, M Redl + Show 2 more

Open Access

https://doi.org/10.1007/s41348-020-00376-0

Copy DOI

Abstract

Ascospores of grape powdery mildew (Erysiphe necator Schw.) play a crucial role in the disease onset in spring in many vine-growing areas. We investigated the physiological maturation of chasmothecia and the time of the first potential ascospore release in three grape-growing areas in Austria by providing standardized conditions for ascospore release in the laboratory and excluding the environmental influence for the release itself. In the overwintering season 2017/2018, the potential ascospore release started in March 2018 in all three investigated wine-growing areas, while in 2018/19, the potential ascospore release was already possible in autumn 2018. Autumn 2018 was characterized by higher temperatures than autumn 2017. We related accumulated degree days (base 8 °C) after chasmothecia formation with the time of first potential chasmothecia dehiscence and found that more than 480 degree days are necessary to reach physiological maturity of chasmothecia. Temperature significantly influenced the dynamics of the potential of ascospore release. More than 50% of the total potential of ascospore release occurred before bud break in both years. Furthermore, weather factors affecting the actual ascospore release in the field were studied. Precipitation and leaf wetness showed a significant positive correlation with ascospore release in the vineyard. In contrast to the potential release, only a small percentage of actual release in the field occurred before bud break, while 84 and 95% of total trapped ascospores were found between bud break and flowering in 2018 and 2019, respectively. Our results reveal that the potential release and actual release have to be combined to predict ascospore release in spring.

Highlights

Grape powdery mildew, caused by Erysiphe necator Schw. [syn
The three vineyards were sprayed with fungicides against powdery mildew until BBCH 79, considering that chasmothecia were formed on leaves from mid-August and reflecting the start of chasmothecia formation in poorly sprayed vineyards in Austria (Steinkellner and Redl 1998)
Potential of ascospore release from chasmothecia and viability of ascospores The ascospore release in autumn differed between both years of this study: in October 2017, chasmothecia collected from the three vineyards at Krems, Vienna and Illmitz did not release any ascospores under laboratory conditions (Table 1)

Summary

Introduction

Grape powdery mildew, caused by Erysiphe necator Schw. [syn. Uncinula necator (Schw.) Burr.], is one of the most important diseases in the world’s grape-growing regions. Primary infections can arise from overwintering mycelia in buds of vines (Sall and Wrysinsky 1982) or from ascospores produced in chasmothecia (Pearson and Gadoury 1987). The latter are considered as the most common. After initiation of chasmothecia formation, they take up to 4 weeks to reach their morphological maturity (Gadoury and Pearson 1988) At this stage, they cannot yet dehisce in the presence of free water. It was shown that weather factors, especially rainfalls, play a key role for the actual ascospore release in the vineyard (Gadoury and Pearson 1990; Jailloux et al 1999; Rossi et al 2010)

Objectives

Methods

Results

Conclusion