Characterization of the fungi associated with ascochyta blight of field pea in Alberta, Canada

Ascochyta blight, caused by a complex of Mycosphaerella pinodes, Phoma pinodella, Ascochyta pisi, and/or Phoma koolunga, is a devastating disease of field pea. In order to understand the composition of fungi associated with ascochyta blight in Alberta, Canada, a total of 157 single-pycnidiospore fungal isolates were obtained from diseased pea samples collected from central and northern Alberta in 2011. These isolates were characterized for species identity, aggressiveness, DNA sequence variation in the internal transcribed spacer (ITS) region, and random amplification of polymorphic DNA (RAPD) patterns. The ITS sequences obtained from 142 fungal isolates were all identical to the ITS sequences from M. pinodes and/or P. pinodella. Inoculation of the 157 isolates on a susceptible pea cultivar Midas indicated that most of the isolates were moderately to highly aggressive. Phylogenetic analysis based on the RAPD data revealed two main groups and six sub-groups, with one main group comprising 78% of the 157 isolates. Distinct RAPD patterns were associated with isolates from particular geographic locations, but were not generally associated with isolate aggressiveness.