RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS OF MITOCHONDRIAL-DNA OF PHYTOPHTHORA-INFESTANS

Mitochondrial (mt) DNA has been prepared from 24 isolates of Phytophthora infestans from 11 countries and analysed for the occurrence of restriction fragment length polymorphisms using six restriction endonucleases. An insertion of about 2 kilobase pairs has been detected in mtDNA of five of the isolates and the approximate site of insertion located on the restriction map of P. infestans mtDNA. The insertion occurred in four out of eight isolates of A2 mating type, but in only one out of 15 isolates of A1 mating type. The insertion occurred in mtDNA from isolates from Brazil, Egypt, U.K. and U.S.A., suggesting a global distribution. Two further polymorphisms were detected which could have been due to single base changes or very small deletions or insertions. One of these, in mtDNA lacking the insertion, occurred in four isolates which, although obtained from four different countries (Brazil, Ireland, U.K. and U.S.A.), appeared fairly uniform with respect to nuclear markers and may be closely related.