The Necessity of Periodic Retesting of Virus-Free Regenerated Grapevine

Fanleaf virus (GFLV), arabis mosaic virus (ArMV), leafroll associated viruses 1+3 (GLRaV-1+3) and fleck virus (GFkV) are the most widespread and damaging grapevine viruses. The releasing in the culture of a high biological value propagation material requires the selection of healthy genotypes for both propagation and use in new clone/varieties production programs. Thus, virus elimination methods are often needed to regenerate healthy plants. In this study, virus-free grapevine genotypes regenerated by various methods (in vivo and in vitro thermotherapy, in vitro chemotherapy, electrotherapy in continuous electric field, direct stimulation with high frequency electrical currents, electrotherapy in horizontal electrophoresis tank) were several times ELISA retested to confirm the diagnostic. The virological tests revealed the recurrence of viral infection after 5 (GLRaV-1+3 and GFKV), respectively 6 years (GFLV, GVA, viral complexes) in plants regenerated by in vivo thermotherapy. GLRaV-1+3-free grapevine plants obtained by in vitro thermotherapy have maintained their acquired phytosanitary status for 4 years. From the electrotherapy methods, in the case of the stimulation with high frequency electric currents, the viral infection reappeared after 3 years. To date, in vitro chemotherapy offers increased safety, only GFLV infection re-emerging after 7 years. These results highlight the need of periodic viruses testing for the safe establishment of plants phytosanitary status. What is the number of sufficient vegetation periods to establish the viral diagnosis remains to be studied.