A survey of tomato and potato fields in Florida reveals unique genotypes of phytophthora infestans between 2005 and 2007

Abstract

Late blight, caused by Phytophthora infestans, affects tomatoes and potatoes in Florida during the winter-spring crop season. During the 2005 season, severe late blight epidemics were observed in Florida prompting our survey. Isolates from2005 to 2007 were characterized phenotypically based on growth on threemedia, mating type, pathogenicity, and sensitivity to metalaxyl and genotypically based on two isozymes, mitochondrial DNA (mtDNA), and genomic profiling using the RG57 probe. Isolates collected in this survey were all A2, mtDNA Ia, and either 100/100 (2005), or 100/122 (2006/2007) at the Gpi locus, and homozygous 100 at the Pep locus. Novel genotypes infecting tomato in Florida were observed based on the Gpi locus and RG57 genomic profile. We propose US-20 for the collection of clonal isolates recovered during the 2005 season and US-21 for clones recovered during 2006 and 2007. In addition to these novel genotypes recovered from tomato, one isolate was recovered from potato representing the US-8 clonal lineage. The findings of the survey in south Florida and their implications are presented.