Rapid PCR-based detection of Phytophthora citricola in naturally infested soil samples using a synthetic bait

In a natural forest stand and two tree nurseries, being affected by the current episode of European oak decline, the presence of the root rot-causing Phytophthora citricola was confirmed by using a newly developed synthetic bait. The bait, consisting of an agar-coated filter paper, which was impregnated with drops of a Phytophthora selective medium (PSM) with added polygalacturonic acid, as an attractant of zoospores, was used to test flooded soil samples. Following DNA extraction, such baits enable fast and reliable PCR-based detection of the pathogen within 2 days. The novel technology of synthetic baits shows a greater sensitivity than natural oak leaflet baits, which are also of very restricted availability. The potential of the synthetic bait as a universal tool in large-scale screening programmes, necessary to manage the risk of root-rot diseases in oak forests and nurseries and orchards, is discussed.