Perhaps the combined effects of the TuYV P0 RNAi silencing suppressor (RSS) activity, putative CMoV derived NMD resistance, and stalling of XRN1 degradation by ST9 could explain the drastic increases of TuYV and CMoV in co-infections of these three viruses and the severe symptom development. The gene discussed is XRN1; the disease is coinfection.