A combination of baiting and PCR techniques for the detection of Phytophthora quercina and P-citricola in soil samples from oak stands

A description is given of the use of a combination of polymerase chain reac tion (PCR) and baiting techniques for the specific detection of Phytophthor a quercina and Phytophthora citricola from soil around declining oak trees. The soil was flooded with water and subjected to a. specific halting proce dure using Quercus robur leaflets as baits. Single round or nested PCR, res pectively, with species-specific primers allowed the detection of P. querci na and P. citricola in infected oak leaflets used as baits and in the water from the same bait tests. PCR detection of both fungi was also after soil samples had been thoroughly mixed with water and the floating organic debri s had been collected. Phytophthora quercina and P. citricola could be readi ly detected almost every case in the water from these tests by PCR bur less frequently in the organic debris. The identities of P. quercina and P. cit ricola were confirmed bu restriction digests of the corresponding PCR ampli cons. The presence of both fungi was also confirmed in parallel in soil sam ples tested h, zoospores of P. citricola and 300 zoospores of P. quercina u sed allowed the detection oi as few as five baiting with oak leaflets. Nest ed PCR with the P. quercina in a volume of 100 mul. The methods presented h ere allow detection and identification of species of Phytophthora in soil w ithout the need for direct extraction of soil samples, and without specific knowledge of the morphological characteristics of the genus.