Co-Authors:
Elad, Y., Department of Plant Pathology and Weed Research, Agricultural Research Organization, Volcani Center, Bet Dagan, Israel
Omer, C., Department of Plant Pathology and Weed Research, Agricultural Research Organization, Volcani Center, Bet Dagan, Israel, Section Agroecology and Plant Health, Robert H. Smith Faculty of Agriculture, Food and Environment, Hebrew University of Jerusalem, Rehovot, Israel
Nisan, Z., Department of Plant Pathology and Weed Research, Agricultural Research Organization, Volcani Center, Bet Dagan, Israel
Harari, D., Central and Northern Arava RandD, Arava, Israel
Goren, H., Eden Research Station, Emek hama'Aynot R and D, Emek Hama'aynot, Israel
Adler, U., Agricultural Growers Council, Yehud, Israel
Silverman, D., Extension Service, Israel Ministry of Agriculture and Rural Affairs, Bet Dagan, Israel
Biton, S., Extension Service, Israel Ministry of Agriculture and Rural Affairs, Bet Dagan, Israel
Abstract:
Sweet basil (Ocimum basilicum) is an annual herb crop grown in polyethylene-covered structures in Israel. It is Israel's leading herb crop, grown in warm regions of the country. Downy mildew (caused by Peronospora belbahrii) is a severe disease in Israel and in many other crop-growing regions worldwide. Experiments were carried out to identify potential climate-management techniques for suppression of this disease on basil in non-heated greenhouses. Disease severity was evaluated under commercial-like conditions in three experiments, with 8-10 walk-in tunnels at each location. Pathogen inoculum was introduced into all walk-in tunnels. Regression analysis was performed between the disease values and air temperature, relative humidity (RH) and soil temperature. Downy mildew severity was negatively related to high (>25°C) air temperature, RH in the range of 65-85% and high (>21°C) soil temperature. The increase in air temperature did not result in a significant increase in leaf temperature; canopy surface median temperatures only reached 30°C. Symptomless plants from relatively warmer tunnels (peak temperatures of 45-48°C) that were transferred to conditions that promote downy mildew (22 ± 2°C, RH > 95%) became severely diseased, showing sporulation of P. belbahrii, suggesting that infection occurred but at the high temperatures symptom expression/tissue colonisation was suppressed. Pot experiments in which aerial and subterranean plant organs were differentially heated revealed that treating the roots with a high temperature (26-31°C), similar to the soil temperatures in the warmer greenhouses, while maintaining the upper plant parts at ambient temperature (20°C), suppresses canopy downy mildew. The effect lasted for 1-2 weeks after the plants were removed from the heated soil treatments and maintained under optimal conditions for pathogen development. Furthermore, oospores were found in the symptomatic leaves. Oospores are minimally affected by high temperature, and therefore the high temperature presumably did not affect pathogen survival. In conclusion, the effect of high greenhouse temperature on basil downy mildew may not result from a direct negative effect of high temperature on the pathogen but from an indirect high-temperature effect on the host, rendering it less susceptible to pathogen development. © 2016 Association of Applied Biologists.
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