Detection and elimination of viruses in callus, somatic embryos and regenerated plantlets of grapevine.

The distribution of some grapevine viruses in flower explants, embryogenic and non-embryogenic calli, single somatic embryos and plants regenerated from embryogenic cultures was investigated by RT-PCR and ELISA. Immature anthers and ovaries of the cultivars Grignolino infected by GRSPaV, GLRaV-1 and GVA, Mu¨ ller-Thurgau infected by GRSPaV and GLRaV-3 and Bosco infected by GRSPaV were cultivated on media inducing indirect somatic embryogenesis. Viruses were detected both in anthers and ovaries. Four months after culture initiation 65.6% of tested calli were infected by at least one virus; high percentages of virus infection were found in calli originating from ovaries. No virus was detected in calli tested 8 months after culture initiation, as well as in single somatic embryos or in embryo-derived plantlets. Somatic embryogenesis confirmed its effectiveness in eliminating phloem-limited grapevine viruses. Regeneration of RT-PCR negative plantlets occurred even when at least a sector of the callus was still infected: the mechanism whereby somatic embryos are freed of some viruses could be related to the rapid proliferation of embryogenic cells within the callus or to the origin of the embryogenic callus from virusfree cells within the original explant.