Phytophthora tentaculata su gerbera in Italia

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Abstract:

During spring 2002, gerbera (Gerbera jamesonii) plants showing blighted leaves and crown and stem rot symptoms were observed in a commercial gerbera planting located at Torre del Greco, near Naples. A Phytophthora sp. was consistently isolated from stem and collar tissues of symptomatic plants. The isolated oomycete was later further investigate, using traditional and polymerase chain reaction (PCR)-based methods to determine species identity, as well as to test pathogenicity. On V8a-juice agar medium at 21±1°C, the observed morphological characters were similar to those of P. tentaculata whereas colony growth ceased at 32-34°C. Sequence analysis of PCR-amplified nuclear ribosomal DNA (rDNA), which includes the internal transcribed spacer (ITS) regions, ITS1 and ITS2 and 5.8S, obtained in template DNA extracted from pure culture fresh mycelium, revealed that the Italian Phytophthora sp. infecting gerbera was most closely related to P. tentaculata infecting Chrysanthemum, which had been reported from Germany. Also, extensive restriction fragment length polymorphism (RFLP) analysis of the rDNA repeat (ITS1, 5.8S and ITS2), using several restriction endonucleases, showed that the gerbera-infecting oomycete differed from several other Phytophthora species used for comparison, and had restriction fragments identical to those known from the German P. tentaculata. Thus, on the basis of biological, morphological and molecular data obtained, the chromist infecting gerbera in Italy was identified as P. tentaculata. Also, it proved to be the causal agent of crown and stem rot of gerbera according to Koch's rule fulfilment. This is the first report of the presence of P. tentaculata in Italy and further extends knowledge on the natural host range of such chromist.

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