Cross‐reactivity of antiserum raised against Phytophthora fragariae with other Phytophthora species and its evaluation as a genus‐detecting antiserum

Antiserum (anti‐PfM) raised against mycelial suspensions of Phytophthora fragariae isolates reacted strongly with antigens from several Phytophthora species. Some cross‐reactions with antigens from Pythium species were decreased by fractionating on an affinity column of Sepharose 4B bound to extracts of Fragaria vesca roots infected with P. fragariae. The affinity‐purified anti‐PfM retained its high cross‐reactivity with the various Phytophthora species tested. It also detected infection of raspberry and strawberry roots by some Phytophthora species. This antiserum could, therefore, prove useful as a broad‐spectrum Phytophthora‐detecting antiserum. Anti‐PfM could not be made specific for P. fragariae because it was raised against components shown to be antigenically similar in all Phytophthora species tested. However, immunoblotting with the affinity‐purified anti‐PfM produced distinct patterns for P. fragariae, P. erythroseptica and P. cactorum: three serotypes were identified for the latter species. This antiserum might therefore prove useful in classifying Phytophthora species.