Few recent investigations examine coinfection interactions between fungal and viral plant pathogens. Here, we investigated coinfections between Leptosphaeria maculans and turnip mosaic virus (TuMV) in canola (Brassica napus). L. maculans causes blackleg disease, canola’s most important yield-limiting fungal pathogen, its spores being spread by wind and rain. TuMV is a major pathogen of Brassica crops, and its spread occurs mainly by aphid vectors but also through seed-to-seedling transmission. Different combinations of L. maculans isolate P11 and resistance breaking isolates L. maculans UWA192 and TuMV 12.1, were inoculated to three cultivars with differing pathogen resistances/susceptibilities. They were inoculated first to entire or half cotyledons 10-12 days after emergence, and second to opposite entire or half cotyledons on the same day (day 0) or 3 or 7 days afterwards. The parameters measured were L. maculans cotyledon disease index (%CDI), and TuMV systemically infected leaf symptom intensity (SI) and virus concentration (VC). Except when both day 0 inoculations were with isolate UWA192, %CDI values were supressed strongly or only weakly when isolates P11 and/or UWA192 were inoculated to plants with L. maculans single gene resistance (SGR) or polygenic resistance, respectively. However, except when isolate P11 was inoculated first and UWA192 second, these values declined after inoculation day 0 when SGR was absent. TuMV infection suppressed %CDI values, although this decrease was usually smaller following day 0 half cotyledon inoculations. When TuMV temperature sensitive extreme resistance was present and both inoculations were with TuMV, SI and VC values diminished greatly. However, the extent of this decrease was reduced when second inoculations were with L. maculans. SI and VC values were also smaller when SGR was present and second inoculations were with L. maculans. When L. maculans resistance was lacking, SI and VC values were smaller when second inoculations to entire cotyledons were with L. maculans rather than TuMV. This also occurred after second half cotyledon inoculations with isolate P11 but not isolate UWA192. Therefore, diverse intra or inter-pathogen interactions developed depending upon host resistance, isolate combination, cotyledon inoculation approach and second inoculation timing. In conclusion, this is the first in depth study to investigate fungus-virus interactions in canola and their effects on diverse host resistances. We found that coinfection between L. maculans and TuMV can play an important role in disease symptom development and the effectiveness of diverse host resistances against these two pathogens. Since individual infections with L. maculans or TuMV both cause major disease losses in diverse Brassica crops growing in different world regions, and TuMV also severely damages crops in other plant families, this study with coinfecting canola pathogens provides an important initial foundational step for further research on the effects of co-occurring pathogens on the effectiveness of host resistances in both these and many other crops.