Assessment of the cicer gene pool : molecular variability and ascochyta rabiei resistance screening

A comprehensive understanding of the genetic variation available within Cicer collections is important for the efficient selection of parents, for introgression of genetic material into superior cultivated lines and for the implementation of effective genetic conservation programs. Wild Cicer relatives may offer alternate genetic sources that may be incorporated into the cultivated chickpea. The aim of this thesis was to investigate the genetic relationships and diversity that exist within the unique Cicer germplasm collection and evaluate it for novel sources of resistance to Ascochyta rabiei. Amplified Fragment Length Polymorphism (AFLP) analysis was used to evaluate the genetic variation among cultivated chickpea and wild Cicer relatives. In total, 214 marker loci were assessed, of which 211 were polymorphic across the 95 accessions that represented 17 species of Cicer. The highest instraspecific variation was detected in C. pinnatifidum and the lowest was in C. macracanthum. Three main species groups were identified by UPGMA clustering using Nei's pair-wise distance calculations. Group 1 included the cultivated species within which C. reticulatum accessions were clustered closest to the C. arietinum cultivars Lasseter, Kaniva and Bumper, supporting the hypothesis that C. reticulatum is the most probable progenitor of the cultivated species. Cicer bijugum, C. judaicum and C. pinnatifidum were clustered together creating Group 2. Group 3 contained all nine perennial species assessed and two annual species C. yamashitae and C. cuneatum. The genetic distance detected between Group 1 and Group 3 (0.13) was equivalent to the genetic distance detected between Group 1 and Group 2 (the primary and annual tertiary species respectively; 0.14). This indicated that the perennial tertiary species may be as valuable for increasing variation to incorporate novel germplasm in the cultigen as the annual tertiary species. Chickpea world germplasm collections were reported to contain a low frequency of ascochyta blight resistance and a narrow genetic basis that could limit the progress of chickpea breeding program. In an effort to screen for novel sources of resistance to ascochyta blight, fifty-six accessions of eight annual wild Cicer species were evaluated under a controlled environment that was optimal for A. rabiei growth. Seven out of the 56 accessions tested (including susceptible control accessions) were classified resistant or tolerant to ascochyta blight at 21 days after inoculation. Among the wild species, C. judaicum was the most resistant species with four accessions showing resistance, whereas C. reticulatum was the most susceptible with no resistant accession rated