VIRUS PROBLEMS IN HORTICULTURAL CROPS
Firstly, isolation and identification of the viruses present in the crop is essential; many diseases result from complex infections with several viruses. Secondly, heat treatment and/or meristemtip culture can usually produce a few virus-free plants for a foundation mother stock. Thorough indexing tests are vital.
The virus-free clones are propagated separately, under conditions of maximum quarantine security, and some progeny from them are meanwhile assessed for horticultural quality. The best clones are then multiplied, and the progeny fed through a nuclear stocks scheme to provide healthy planting material for the grower.
As field stocks break down through re-infection, they are replaced by more progeny from the foundation stocks, which are always held under maximum hygiene security.
The life of a field stock varies according to local conditions, but should become greater over the years as infected stocks become 'diluted out' with repeated supplies of clean stock.
The techniques concerned have been described by Hollings and Stone, Sci. Hort., 20:57–72, 1968.