Resistance Phenotypes in Diverse Accessions, Breeding Lines, and Cultivars of Three Mustard Species Inoculated with Turnip mosaic virus.

The responses of 44 accessions, breeding lines, or cultivars of Brassica juncea (Indian mustard), 9 of B. carinata (Ethiopian mustard), 5 of B. nigra (black mustard), and 6 crosses between B. juncea and B. napus (canola) to sap inoculation with Turnip mosaic virus (TuMV) were investigated. Eleven different phenotypes were obtained, including six previously recognized in B. napus (+, O, R, RN, RN/+, and +N) and five not recorded before (+St, RN/St, RN/St/+, +N1, and +ND). All but two (+ and +St) were resistance phenotypes. The resistance phenotypes in B. carinata and B. juncea × B. napus crosses prevented systemic infection but those in B. juncea and B. nigra included systemic necrosis. Absence of systemic invasion associated with resistance phenotypes in B. carinata was confirmed by graft inoculations. The resistance phenotypes may reflect the presence of known TuMV resistance genes located in the A genome or unknown genes in the B genome in B. juncea, unknown resistance genes in the B or C genomes in B. carinata, and unknown resistance genes in the B genome in B. nigra. Further research to identify the resistance genes involved would establish the potential usefulness of these resistance phenotypes in breeding TuMV-resistant mustard cultivars for biofuel production.