Gene flow of Phytophthora infestans between organic and conventional potato field in Southern Flevoland, The Netherlands

Phytophthora infestans causes a devastating disease of potato and tomato. P. infestans can reproduce asexually and sexually; and both mating types have been detected in several European countries since the early 1980s. Previous work in the Netherlands showed that population is highly diverse due to sexual reproduction and that oospores can overwinter in the soil. In Southern Flevoland, the genotypic diversity was analyzed by characterizing isolates from conventional and organic potato fields, potato refuse piles, and allotment gardens for mating type and DNA fingerprints between 1994 and 1996. Refuse piles were identified as the most important infection source for commercial fields in 1994 and 1995 and some organic fields were identified as a source of mid-season infection of conventional fields; however, only RFLP fingerprint patterns were used for the analysis. We sampled DNA from these populations and amplified two regions of a single-copy nuclear ras gene (intron 1 -224 bp and exon 3-6 -542 bp) containing both coding and noncoding regions to elucidate gene flow between organic and conventional fields. Multiple isolates were sampled from 5 organic, 17 conventional and 7 refuse pile sites. There were 5 heterozygous sites in the intron 1 region and 5 heterozygous sites in the exon 3-6 region that were phylogenetically informative. Only two isolates from an organic and conventional field were homozygous. Five haplotypes were found among the fields and three of these were found in our previous world wide study of Andean migration. Further analyses of additional mitochondrial gene regions are underway to investigate the migration of P. infestans between these fields.