Application of molecular markers to study ascochyta rabiei : the causal agent of ascochyta blight of chickpea

Chickpea (Cicer ariatium L.) is an important legume crop in Australia. A major limiting factor of chickpea production is ascochyta blight, a devastating disease, caused by the fungal pathogen Ascochyta rabiei (Pass.) Labrousse. A specific molecular marker was identified based on restriction fragment length polymorphism (RFLP) analysis of polymerase chain reaction (PCR) for pathogen identification. From the marker, a diagnostic test was developed for the fast, specific, sensitive and reliable detection of the pathogen in infected leaves and seeds of chickpea. A study of the genetic structure of a population of A. rabiei isolates, sampled from the five chickpea-growing states in Australia, revealed a relatively low level of genetic diversity among the isolates while there was a high level of genetic variation found between Australian and overseas A. rabiei isolates as well as among the overseas isolates. Gene flow was high among Australian chickpea growing regions. It is therefore important to prevent the new introduction of the more diverse overseas isolates into Australia. The heterothallic nature of the mating system of A. rabiei is largely responsible for the increases in genetic diversity and adaptive potential of this pathogen. To identify which mating type was present in the field and in the laboratory collection, how they were distributed in the population, and the role they played in the population genetic structure of the pathogen; a molecular marker were developed for the mating type 1 (MAT-1) of A. rabiei. To successfully control a disease, genetics of important traits such as resistance in the host as well as mating type, avirulence/virulence, and fungicide resistance in the pathogen need to be understood. A genetic linkage map of A. rabiei was constructed in this project to facilitate such studies by providing a framework for the location and inheritance of such important traits.