THE CONTROL OF HOP LATENT VIROID IN UK HOPS

Plants free from hop latent viroid (HLVd) were obtained from infected material by culturing meristems cut from hop plants that had been kept at 2-4°C for periods of 8-21 months. A total of 77 plants of six cultivars or selections were grown from meristems and 28 of these were free from HLVd. Viroid-free plants can be infected mechanically and this is particularly likely to occur during propagation but it can also occur in commercial gardens. Plants in a commercial garden were inoculated by cutting with a razor blade or by rubbing bines together at intervals during 1992 and 1993. More plants became infected by cutting than by rubbing and most infection occurred in May, before the plants had grown large enough for significant contact between neighbouring plants. There was no transmission of HLVd to 30 hop plants exposed to a total of 1750 Phorodon humuli that had fed on infected source plants.