Survival in the field of Pseudoperonospora cubensis and Plasmopara viticola after extreme hot and dry weather conditions
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Survival in the field of Pseudoperonospora cubensis and Plasmopara viticola after extreme hot and dry weather conditions in Israel Yigal Cohen
&
Moshe Reuveni & Lior Gur & Shmuel Ovadia
Received: 17 June 2020 / Accepted: 12 August 2020 # Springer Nature B.V. 2020
Abstract Unprecedented hot and dry spells occurred all over Israel for six days, from May 16 to May 21, 2020. Maximal air temperature reached 46.5 °C and minimal relative humidity reached 10%. The total number of hours with temperature of ≥40 °C was 45 and 41 in the coastal plain and the Judean mountains foothills, respectively. The downy mildew pathogens of cucumber and grapevine survived this extreme event, showing a rapid revival in nature soon after the heat wave. The current isolates of these oomycetes seem to be more tolerant to heat compared to the isolates of the previous century. Keywords Climate change . Cucumber . Global warming . Grapevine . Oomycetes . Fungi . Peronosporales . Plant pathogen . Plant disease
Introduction Climate change is projected to be a powerful stressor on terrestrial ecosystems in the second half of the twentyY. Cohen (*) Faculty of Life Sciences, Bar-Ilan University, 52900 Ramat Gan, Israel e-mail: [email protected] M. Reuveni : L. Gur Shamir Research Institute, University of Haifa, P.O. Box 97, 12900 Katzrin, Israel S. Ovadia Carmel Winery, Zichron Yaacov, Israel
first century, especially under high-warming scenarios (IPCC 2014). According to model projections, a range of climate change-related variables (extreme events and changes in precipitation, temperature, and CO2) will continue to exacerbate the establishment and spread of pests and pathogens (IPCC 2014). Oomycete plants pathogen causing downy mildews and late blight require moderate temperatures for their development. The highest degree of sporulation and colonization of Peronospora tabacina in tobacco leaves is 15 and 20 °C, respectively. Exposure of infected tobacco plants to 24-48 h at 35o C or 6-12 h at 40 °C is lethal to the pathogen (Rotem and Cohen 1970). Phytophthora infestans was killed in blighted potato plants after exposure of 24 h to 35 °C or 12 h to 40 °C (Rotem and Cohen 1974). Peronospora belbahrii affecting sweet basil could not withstand exposure to high temperatures. Exposure of spores, infected leaves, or infected plants to 35–45 °C for 6-9 h dismissed its survival (Cohen and Rubin 2015). Sporulation potential of Pseudoperonospora cubensis was highest when infected cucumber plants were incubated at 15 °C continuously or at 20:15 °C day: night thermo-periods (Cohen and Rotem 1971a). Infectivity of dispersed sporangia of P. cubensis was reduced to nil at 35 °C (Cohen and Rotem 1971b, c). Water content of healthy cucumber leaves is about 18 mg.cm2. Inoculation with P. cubensis decreased this water content by 50% during leaf colonization (Oerke et al. 2006). Lower leaf water content may reduce thermal mortality of the mycelium. In Israel’s Jordan Valley in mid-summer with mean temperatures of 28-30 °C no downy milde
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