Analysis of genetic and pathogenic variation of Alternaria solani from a potato production region

A two-year survey was conducted to investigate the level of genetic variability occurring across growing seasons within natural populations of Alternaria solani, the cause of early blight in potato. Genetic diversity among 151 isolates, taken from a disease resistance breeding trial, was assessed using seven random amplified polymorphic DNA (RAPD) primers and sequence analyses of portions of the internal transcriber spacer (ITS) region and Alt a1 gene. A. solani isolates were grouped into 19 RAPD profiles to examine the distribution patterns of genetically distinct isolates within and between years. Seven RAPD profiles were found spanning both years with profiles 6 and 13 being the most prevalent. Five unique profiles were found only in 2008 and seven were found only in 2009. No variation was observed among isolates of A. solani based on ITS and Alt a1 sequence analyses, but a distinction between A. solani and A. dauci, a close relative outgroup was identified. Pathogenicity was also assessed using a tissue culture plantlet assay on four isolates and two reference cultures. Differences in virulence were observed among the isolates examined.