MONITORING PRUNUS NECROTIC RINGSPOT VIRUS-INFECTION BY HYBRIDIZATION WITH A CRNA PROBE AFTER IN-VITRO MICROGRAFTING

In vitro micrografting was tested as a technique for inoculating peach [Prunus persica (L.) Batsch] shoot cultures with Prunus necrotic ring spot virus (PNRSV). Cultured 'Suncrest' shoots derived from a naturall y infected tree (as indicated by ELISA testing) maintained virus in vi tro, with virus concentrations in growing tips and folded leaves being several times those of fully expanded leaves, Infected shoots served as graft bases and source of the virus. Grafted tips were derived from 'Suncrest' trees that had tested negative for the virus, Leaf samples were collected from the tips following grafting and analyzed for the presence of virus by slot-blot hybridization with a (DIG)-labeled cRNA probe derived from PNRSV RNA 3. Rates of successful grafting ranged f rom 55% to 73% in three trials and PNRSV was found in all tips analyze d. Virus concentrations approximated those found in source shoots, sug gesting that in vitro micrografting should be useful for screening tra nsformed peach shoots for coat protein-mediated resistance to PNRSV. C hemical name used: digoxigenin (DIG).