TWENTY-FOURTH ANNUAL EASTERN FISH HEALTH WORKSHOP Royal Pavilion Resort, Atlantic Beach, NC MARCH 9-11, 1999 Analysis Of Genetic Variation In Strains Of The Oyster Pathogen Perkinsus marinus Kimberly S. Reece1, David Bushek2 and Karen L. Hudson1 1Virginia Institute of Marine Science, The College of William and Mary, Gloucester Point, VA 23062; 2Baruch Marine Field Laboratory, University of South Carolina, Georgetown, SC 29442. Perkinsus marinus is a major pathogen of the eastern oyster Crassostrea virginica. Recently developed in vitro culture and cloning methods have allowed us to examine the population genetic structure of P. marinus using molecular genetics. The genetic relatedness of P. marinus in vitro cultures and their clonal composition has been examined using isolates collected from throughout the U.S. Atlantic and Gulf coasts. DNA isolated from 63 primary cultures and 88 clonal cultures derived from these isolates was examined at six polymorphic loci by restriction fragment length polymorphism analysis. Comparison of clonal and primary culture genotypes indicated that primary isolate cultures from a single oyster can be polyclonal, evidence that oysters can be infected with multiple strains. Heterozygous genotypes for several clonal cultures suggested that cultured P. marinus cells were diploid, a fact confirmed by DNA sequence analysis of alleles at two anonymous single copy loci in heterozygous clonal cultures. Allele sequences were identical in isolates from geographically distant sites, but allelic and genotypic frequencies differed significantly among the Northeast, Southeast and Gulf coast regions. Overall, there were fourteen different composite genotypes detected with more than 80% of the isolates possessing one of three predominant genotypes. One of the major composite genotypes was unique to Gulf coast isolates. Genetic distance analysis indicated three major genotypic clades, each containing one of the three major genotypes. Return to 24th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page