Molecular Identification and Detection of Phytophthora melonis Based on Nuclear and Cytoplasmic Genome

The plant pathogen Phytophthora melonis is morphologically similar to some other non-papillate Phytophthora spp. especially P. drechsleri and therefore it is difficult to discriminate these convergent taxa. This study was performed to design specific primers based on nuclear and cytoplasmic genome, examine their specificity against other convergent species, and optimize the specific primers’ conditions to detect P. melonis. Nine nuclear and four cytoplasmic genes were appropriate to design thirteen specific primers based on their nucleotide polymorphism. PCR conditions were optimized. Phytophthora melonis were detected by specific primers in inoculated plants such as cucumber, watermelon, melon, sugar beet and pistachio. All specific primers detected pathogen in 1:100 (pathogen: soil) inoculated soil.Up to 10 zoospores per milliliter were detected using nested polymerase chain reaction. ITS-MF1 and ITS-MR2 (ITS-M2 set, from internal transcribed spacers of rRNA gene) were selected as the most efficient primers based on their specificity and sensitivity. The optimized annealing temperature for this primer set was 68 °C. It seemed that nested PCR by ITS-M2 primer set together withthe universal primers ITS6 and ITS4 as external primers is at least 106 times more sensitive than simple PCR. Multiplex polymerase chain reaction simultaneously detected the three cucurbits’ pathogens including P. melonis, P. nicotianae and P. drechsleri. This study showed that the designed primers could be effective tools for detection of P. melonis isolates from infected tissues, and infested water and soil.