Intraspecific variation in Phytophthora citrophthora from citrus trees in Eastern Corsica

Isolates of Phytophthora pathogenic to citrus crops on Eastern Corsica and associated with gummosis were identified by PCR-RFLP of internal transcribed spacers (ITS) sequences and characterized by the random amplified microsatellites (RAMS) technique. A sample of 114 isolates collected from diseased trunks and fruits, and from soil, were overwhelmingly Phytophthora citrophthora. Further analysis indicated that the P. citrophthora population was not homogeneous in citrus groves. There were two groups, with a few (4%) atypical isolates in two marginal groups. The major groups have been re-examined in the light of mating behaviour, RFLPs of mitochondrial DNA and sequence comparisons of ITS regions of rDNA. They were found distinct with all these criteria and perhaps constitute distinct taxa. The results indicate that important modifications occurred in the population structure of P. citrophthora over time in Corsican groves. These changes may have impact on the recent outbreaks of gummosis.