The Australian Ascochyta rabiei population is diverse in its ability to cause disease on host accessions of differing known levels of resistance, with isolates ranging from low to highly aggressive. In order to strategically manage such a diverse population, information regarding the infection and invasion processes of the pathogen is required. To better understand the diversity in A. rabiei-chickpea interactions, an in-depth histopathology study was conducted with isolates with varying aggressiveness on the four host genotypes previously used to characterise them based on gross disease symptomology. Highly replicated microscopy observations revealed significant differences in percentages, timings and rates of conidiaspore germinations among all of the isolates and on all of the hosts assessed. In general, the previously characterised highly aggressive isolates germinated and penetrated faster than the low aggressive isolate. However, there were significance differences in these rates, indicating that some highly aggressive isolates are able to germinate and invade the host much faster than others within the first 12 hours of contact. This difference in rates continued through to the development of disease symptomology where it appeared earlier and most severe for aggressive isolates on PBA Hatraick and Kyabra. All isolates germinated faster and produced longer germ tubes on the susceptible accession (Kyabra) than on the best resistant accession (ICC3996). Such knowledge may lead to the biological targeting of specific chemical controls and/or aid in decisions around farming practice changes in the presence of this ubiquitous pathosystem