Molecular variability and mating-type frequency of Ascochyta rabiei of chickpea from Saskatchewan, Canada

Molecular variability of populations of Ascochyta rabiei from Saskatchewan collected in 1998 and 2002, and mating-type frequency of isolates from 1998, 2001 and 2002 were assessed. To evaluate the genetic diversity of different A. rabiei populations, 30 isolates from 1998 and 30 isolates from 2002 were compared by random amplified polymorphic DNA fingerprinting. Cluster analysis and analysis of molecular variance suggested differentiation of the 1998 and 2002 populations, yet equal amplicon diversity between populations with the majority of the variation occurring within each population was observed. Analysis of mating-type frequencies on 30 isolates each from 1998, 2001 and 2002 populations did not significantly depart from a 1 : 1 ratio suggesting random mating of each population. However, when 121 isolates from 2002 were analysed for mating type, a significant departure from a 1 : 1 ratio was found suggesting smaller sampling sizes for mating-type frequenciesmay not reveal true differences. In further support of the hypothesis of a randomly mating population in 1998, the Index of Association was not significantly different from zero. However, this measure suggested departure from panamixa in the 2002 population consistent with the skewed mating-type ratio. It was concluded that there was some evidence for genetic shift in populations of A. rabiei between 1998 and 2002, which is consistent with a shift in aggressiveness observed between these populations.