DNA fingerprinting with a set of synthetic oligonucleotides
complementary to simple repetitive sequences was used to develop
molecular markers for Ascochyta rabiei, the most important
fungal pathogen of chickpea (Cicer arietinum). Two compatible
mating
type isolates (MatI and MatII) from the U.S. Pacific Northwest
with the same low level of aggressivity were compared to highly
virulent isolates from the Mediterranean region and Pakistan to find
suitable mating partners for the production of a mapping
population. After Hinf I or Taq I restriction,
electrophoresis and in-gel hybridization with ten different simple repetitive
oligonucleotides, all tested single-spored isolates exhibited unique
fingerprint patterns. The analysis revealed that the two U.S.
mating types share a considerable amount of genetic variability. A total
of 77 polymorphic marker bands were detected. A higher
number of polymorphic bands (up to 104) was observed between these
isolates and those from different geographical regions. The
isolates from the Mediterranean region and Pakistan shared a
lower degree (between 80 and 90 bands) of detectable genetic
diversity. These data permit selection of highly virulent crossing
partners for the different mating types with a high degree of
detectable polymorphism.
A sexual cross was performed to prove the Mendelian segregation of
fingerprint bands for future linkage analysis. Additionally,
the fingerprint data based on 268 informative characters combined with
phenetic and phylogenetic algorithms allow determination of
the genetic identity, relatedness and diversity of the different
isolates. To confirm the phylogenetic data, two outgroupers
Ascochyta fabae and Ascochyta pisi, were included.
Results indicate that A. pisi is more closely related to
A. rabiei than A. fabae.