| This thesis examined the coevolutionary genetics of the lodgepole pine Pinus contorta) - jack pine (P. banksiana) complex in west central Alberta and western gall rust (WGR) fungus (Endocronartium harknessii). It consisted of three studies. First, a greenhouse inoculation study of 23 lodgepole pine, 9 jack pine, and 8 putative hybrid populations using two WGR sources, one each from lodgepole pine and jack pine hosts, was carried out to investigate if hybrids differ from the parental species in WGR susceptibility and if there is host-pathogen interaction. Lodgepole pine and hybrids were significantly more susceptible to WGR infection than jack pine. Both host species were more susceptible to their own rust spore sources, causing significant spore source x host group interactions.; In the second study, the random amplified polymorphic DNA (RAPD) variability was assessed to elucidate single-locus and multilocus structure of hosts using the same populations as in the greenhouse study, and to determine if the level of gene exchange in the hybrid zone is related to WGR susceptibility. Averaged estimates of RAPD diversity were 0.143 for lodgepole pine, 0.156 for jack pine, and 0.152 for hybrids. Based on RAPD variation, lodgepole pine could be separated from jack pine, but hybrids had a closer genetic affinity with lodgepole pine. Significant multilocus associations were found in 29 of 40 populations. Such associations were due largely to Wahlund effect that accounted for 40.7% of multilocus heterozygosity in hybrids, but only 18.6% in lodgepole pine and 16.0% in jack pine.; The level of introgression, as measured by genetic admixtures of parental species, was significantly correlated with WGR susceptibility. Thus, WGR prevalence in this hybrid area would be closely linked to the introgression.; The third study was designed to develop a new complementary model of host - pathogen interaction that allowed for arbitrary levels of dominance in a diploid host. Computer simulations based on this model allowed for examining effects of overdominance, incomplete dominance and underdominance on equilibrium frequencies of resistance gene in a host population and on stability of equilibria. |
