Brassica Yellows Virus and Turnip Mosaic Virus: Asymmetric Interaction in the Mixed Infections in <i>Nicotiana benthamiana</i> and <i>Brassica napus</i> L.

Mixed viral infections are common in the field but are rarely studied due to their inherent complexity. Here, we observed a mixed infection of brassica yellows virus (BrYV) and turnip mosaic virus (TuMV) in oilseed rape (<i>Brassica napus</i> L.). Therefore, this study explores the relationships between two viruses based on newly constructed infectious clones of BrYV-GZA, BrYV-GZB, and a previously reported TuMV-GFP clone. Our results demonstrate that BrYV-GZA significantly inhibited TuMV in <i>Nicotiana benthamiana</i> (<i>N. benthamiana</i>). In contrast, BrYV-GZB was a mild strain, which exhibited a delayed onset time and less influence on TuMV. In oilseed rape, the incidence of TuMV was significantly lower in plants co-infected with BrYV-GZA and TuMV (AT) than in those infected with TuMV alone (<i>p</i> = 0.015). Besides, TuMV failed to infect oilseed rape plants pre-inoculated with BrYV-GZA. Furthermore, RNA silencing suppressors of HC-Pro and P0 were found promote the accumulation of BrYV-GZA and TuMV accumulation, respectively. Symptom analysis showed that both BrYV-GZA single infection and AT double infection significantly reduced the plant height of oilseed rape. Additionally, these infections led to a 3% and 7% decrease in oil content of rapeseed, respectively. AT double infection also altered fatty acid composition, resulting in significant decreases in both oleic acid and stearic acid, and an increase in linoleic acid. Overall, our findings reveal an asymmetric interaction between BrYV-GZA and TuMV in both <i>N. benthamiana</i> and oilseed rape, highlighting the effects of mixed infections on agronomic traits of oilseed rape.