Screening Brassica rapa for broad-spectrum resistance to Turnip mosaic virus

Turnip mosaic virus (TuMV) poses a major threat to Brassica crops like Chinese cabbage, causing significant economic losses. A viable and effective strategy to manage such diseases is by improvement of genetic-based viral resistance. To achieve this, it is important to have detailed and wide-ranging genetic resources, necessitating genetic exploration. To identify useful TuMV resistant genetic resources, we screened geographically and genetically diverse resources including over 90 accessions from the Tohoku Univ. Brassica Seed Bank against eleven TuMV isolates phylogenetically classified into five clusters. Two USA accessions exhibited no or only slight symptoms with no virus protein detected in virus-inoculated and non-inoculated upper leaves, suggesting an extreme resistance to all tested TuMV isolates. Through sequencing and dCAPS analysis of eukaryotic translation initiation factor (eIF4E/eIFiso4E) in the 95 B. rapa accessions, several amino acid substitutions were observed on the dorsal surface and cap-binding sites of eIF4E/eIFiso4E proteins, with three of them significantly associated with resistance/susceptibility responses. When exploring co-infection using TuMV and cucumber mosaic virus (CMV), the TuMV susceptible accession died, but TuMV resistance was retained in the TuMV resistant accession. It suggested that the broad-spectrum resistance in the two USA accessions is a highly valuable resources for Brassica breeding.