Potential and actual ascospore release of Erysiphe necator chasmothecia in Austria
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ORIGINAL ARTICLE
Potential and actual ascospore release of Erysiphe necator chasmothecia in Austria M. Redl1 · L. Sitavanc1 · B. Spangl2 · S. Steinkellner1 Received: 13 July 2020 / Accepted: 29 August 2020 © The Author(s) 2020
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. Keywords Erysiphe necator · Chasmothecia · Ascospores · Degree days · Leaf wetness
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. The principles of the disease’s development are well described. 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 * S. Steinkellner [email protected] 1
Institute of Plant Protection, University of Natural Resources and Life Sciences, Gregor‑Mendel‑Straße 33, A‑1180 Vienna, Austria
Institute of Statistics, University of Natural Resources and Life Sciences, Peter‑Jordan‑Straße 82, A‑1190 Vienna, Austria
2
primary inoculum source in many grape-growing regions (Pearson and Gadoury 1987; Cortesi et al. 1997; Steinkellner 1998; Jailloux et al. 1999; Schneider et al. 1999; Gee et al. 2000; Grove 2004; Rossi et al. 2010; Hoffmann et al. 2012
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