Determination of anti-mildew activity of essential oils against downy mildew of sunflower caused by Plasmopara halstedii
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Determination of anti‑mildew activity of essential oils against downy mildew of sunflower caused by Plasmopara halstedii Yesim Er1 · Nuray Özer2 · Yakup Zekai Katırcıoğlu3 Received: 25 February 2019 / Accepted: 28 February 2020 © Deutsche Phytomedizinische Gesellschaft 2020
Abstract To evaluate the anti-mildew activity of the commercial essential oils (EOs) against pathotypes ‘771’ and ‘773’ of P. halstedii in mineral salt medium, the EOs obtained from different parts of Greek sage, black cumin, bay, mustard, St. John’s wort, French lavender, garlic, grape, and ginger plants were examined at concentrations of 0.2%, 0.4%, 0.6%, 0.8%, and 1% on leaf discs of susceptible sunflower variety ‘08-TR-003’. The ginger EO had the highest anti-mildew activity at a concentration of 1% and was found to be the most effective with a decrease in sporangium quantity above 90% for pathotypes ‘771’ and ‘773’. The EOs of garlic, St. John’s wort, and grape followed it, respectively, with a decrease in sporangium quantity above 80%. Keywords Anti-mildew activity · Essential oil · Leaf disc · Plasmopara halstedii
Introduction Diseases in sunflower (Helianthus annuus L.) are the most significant factor limiting the crop yield and genetic yield potential of sunflower varieties. The downy mildew caused by Plasmopara halstedii (Farl.) Berl. & De Toni is particularly one of the most important diseases of sunflower. When the relative humidity approaches 100% and air temperature is approximately 16–18 °C, it causes apparent white sporulation, firstly on the lower side of cotyledons, and dwarfing of the plants (Viranyi 1978; Sackston 1981; Ljubich and Gulya 1988; Spring 2001; Sakr 2010). So far, the disease has been reported on all continents and is more common in regions with a temperate climate than in regions with a subtropical climate, where sunflower is cultivated, causing significant yield losses due to sporangiospores released from sporangia in epidemic years (Viranyi and Spring 2011). In recent years, the use of chemical pesticides against plant diseases is proposed as the most effective method * Yesim Er [email protected] 1
Istanbul Directorate of Agricultural Quarantine, Istanbul, Turkey
2
Department of Plant Protection, Faculty of Agriculture, Namık Kemal University, Tekirdağ, Turkey
3
Department of Plant Protection, Faculty of Agriculture, Ankara University, Ankara, Turkey
(Gulya et al. 1999; Sudisha et al. 2007, 2009, 2010). The systemic chemical pesticides, which are used to control P. halstedii, can be easily absorbed by soil, and it causes the degradation of the ecosystem and pollution of our foods with these chemicals (Anonymous 1987; Ragsdale et al. 1993; Satapute et al. 2019). Besides, the resistance of target organism as a result of long-term use of systemic pesticides is another disadvantage causing the appearance of metalaxyl-resistant strains of P. halstedii. Although the seed treatment with azoxystrobin as an alternative pesticide has been registered for the control of downy mildew,
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