The 3BS allele of Sumai 3 has been the main source of Fusarium head blight (FHB) resistance worldwide. Using molecular markers and FHB resistance screenings, we have analysed the effects of this allele in two backcross and two 4-way F2 populations derived from elite Australian cultivars. Compared to individuals without the Sumai 3 allele, individuals with the allele showed an average 32.0% reduction in FHB severity as measured by number of diseased spikelets. This value was slightly reduced to 29.2% when the total number of spikelets was taken into account by expressing severity as the proportion of diseased spikelets. When compared to the parental cultivars, progeny with the 3BS allele of Sumai 3 offered, on average, 43.3% reduction in FHB severity. Significant differences were not detected between progeny that were homozygous or heterozygous for the 3BS locus, indicating a dominant inheritance of this locus. These results confirm that the 3BS allele controls a large component of the FHB resistance in Sumai 3, which can be readily incorporated and detected in backcross populations using molecular markers. The materials derived from this study could offer significant benefits to the Australian wheat breeding programs.