Salinity and disease are, respectively, the most important abiotic and biotic constraints to greenhouse crop production in Oman. Sea water intrusion following excessive groundwater extraction for agricultural production has led to a general increase in the salinity levels of irrigation water used across much of northern Oman. Surveys of the EC levels of irrigation water used in greenhouses across the region show that "hot spots" of high salinity occur within well defined areas. According to published tolerances of cucumber to salinity, over 10% of farms with greenhouses in some areas have EC levels at which crop production becomes marginal due to consequent reduced yields. Based on anecdotal evidence, farms with high salinity levels suffer proportionately higher levels of damping-off disease caused by Pythium aphanidermatum. Detailed investigations have indicated that levels of salinity that compromise crop growth have no effect on the ability of P. aphanidermatum to grow in vitro or in vivo. in agar prepared with saline irrigation water, the pathogen grew as well as in agar prepared with distilled water, even when the salinity level exceeds that at which cucumber production is untenable. Similarly, in sand culture, P. aphanidermatum grew and colonized radish seeds even in the presence of highly saline water.
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