A new marker for rapid and early identification and detection of Phytophthora infestans,
the causal agent of late blight of potato and tomato has been developed using PCR. Amplification
products obtained from random amplified monomorphic DNA (RAPD) reactions were cloned and
sequenced, and two extended primer sets (PITH2-F/PITH2-R) were designed from the resulting
data that were used to detect sequenced-characterized DNA markers. A single 1.5 kb DNA amplification
product was consistently obtained from primer OPA 12 that was specific for P. infestans but
was not produced from other Phytophthora species and fungal pathogen of potato. A 524 bp amplification
product was also produced from naturally infected tubers known to be infected with the
fungus as verified by microscopic examination. A similar PCR product was obtained from sterile
soil samples artificially infested with P. infestans inoculums. This primer is a highly specific to P.
infestans only. This PCR based assay enables detection of P. infestans from host tissues, sporangia
and Oospores present in the soil in a single day.