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Turnip mosaic virus (TuMV) causes a damaging disease in Brassica juncea, an important oilseed and biofuel crop. B. juncea gene TuRBJU 01 is associated with a systemic hypersensitive phenotype in TuMV-infected plants. Plants of TuMV-susceptible parent JM 06006, TuMV-resistant parent Oasis Cl (which carries TuRBJU 01) and F3 progeny plants obtained by crossing them were inoculated with 10 Australian TuMV isolates, most of which were already pathotyped. These were: NSW-1, NSW-5 (pathotype 7), NSW-2, NSW-6 (pathotype 1), WA-Ap, WA-Ap1 (pathotype 8), NSW-3, NSW-4 (new pathotype) and 12.1 and 12.5 (unpathotyped B. napus resistance breaking isolates). JM 06006 plants developed a susceptible phenotype with all isolates while a systemic hypersensitive phenotype resulted with all isolates except NSW-3 in Oasis Cl plants. With seven isolates, the segregation ratios for necrotic: non-necrotic phenotypes obtained in inoculated F3 progeny plants all fitted a 3:1 ratio. However, with isolates 12.5 and 12.1, although pooled test segregation data did not fit a 3:1 ratio, individual test data sometimes did. Thus, TuRBJU 01 was less effective against 12.1 and 12.5, and overcome by NSW-3. Also, phenotypic responses obtained with TuRBJU 01 were unrelated to those of TuMV resistance genes present in B. napus differentials. TuRBJU 01 will be valuable in breeding TuMV-resistant B. juncea cultivars.