Molecular and pathogenicity characteristics of Phytophthora nicotianae responsible for root necrosis and wilting of pepper (Capsicum annuum L.) in Tunisia

Isolates of Phytophthora from pepper, produced in Tunisia, were characteris ed according to molecular and pathogenicity criteria. Polymerase chain reac tion amplification of the ITS1 region in the ribosomal DNA resulted in diff erent sized fragments. The pepper isolated and P nicotianae yielded a fragm ent of 310 bp that distinguished it from P. capsici with a fragment of 270 bp. The ribosomal RNA gene amplicons of both internal transcribed spacers a nd the 5.8 S of the pepper Phytophthora and nicotianae were digested with 8 endonucleases. The patterns generated, with the 2 enzymes that cut, were i dentical for both taxa. This molecular analysis corroborated the morphologi cal and biological characteristics and suggests strongly that the isolates of Phytophthora from pepper belong to the species P. nicotianae. Inoculatio n of pepper, tomato, eggplant and tobacco plants with the isolates of Fl ni cotianae from pepper showed they were highly pathogenic on pepper but not o n tobacco, while their pathogenicity was weak on tomato and eggplant and wa s associated with atypical symptoms not observed in the field. These pathog enicity tests suggest that pepper isolates of P. nicotianae are particularl y adapted to their host and may thus constitute a forma specialis of P. nic otianae.