The first objective of this study was to determine the inheritance of resistance to blackleg caused by 'Leptosphaeria maculans' in ' Brassica rapa'. Intraspecific crosses were performed between four blackleg resistant populations and a blackleg susceptible population. Inheritance of resistance to the disease was determined by production of homozygous doubled haploid lines, from heterozygous blackleg resistant F1 generations, using microspore culture and self-pollination to determine the doubled haploid line segregation of the population at the cotyledon and adult plant stages. The second objective of this study was to determine the inheritance of resistance to 'Albugo candida' in 'B. rapa'. Intraspecific crosses were performed between a pure-breeding white rust resistant population to four pure-breeding white rust susceptible populations. Inheritance of resistance to the disease was determined by production of homozygous doubled haploid lines, from heterozygous white rust resistant F1 generations, using microspore culture and self-pollination to determine the doubled haploid line segregation of the population at the cotyledon stage. (Abstract shortened by UMI.)