Relative Disease Susceptibility of Cultivated Varieties of Potato to Different Isolates of Phytophthora Infestans

Abstract

ABSTRACT Late blight, caused by the Oomycete pathogen Phytophthora infestans, continues to be the most devastating and economically important disease affecting potato crops worldwide. Recent geographical migrations of the pathogen have displaced the ‘old’ US-1 clonal lineage with ‘new’, genotypically distinct, lineages. These new genotypes have shown increased pathogenic fitness and diverse environmental requirements. Interactions between two different isolates of the US-8 race and three potato (Solanum tuberosum) cultivars were analyzed through in planta infection, under controlled laboratory conditions. Disease development over time was rated for each experimental unit by determining incubation period, foliar lesion area and relative number of leaves displaying necrosis. Difference in incubation period between isolates was nearly significant in Russet Burbank, with disease symptoms presenting much later for replicates infected with PSUPotb. No significant difference was seen in incubation period between isolates in cv. Kennebec or cv. Red Norland, with the shortest incubation period occurring for isolate NC092ba in Kennebec. Incubation period did not differ for isolate NC092ba across cultivars. Isolate PSUPotb had a longer incubation period in Russet Burbank than in the other two cultivars. Data suggest, therefore, that differential pathogenicity between the US-8 isolates exists in at least one cultivar. Cultivar susceptibility was also variable. As suggested in previous studies, it was found that cv. Kennebec was least susceptible to either isolate. Confirmation of pathogen presence in infected leaf tissue was successfully obtained using previously developed P. infestans specific primers in a standard Polymerase Chain Reaction (PCR) assay.