The distribution and spread of hop latent viroid within two commercial plantings of hop (Humulus lupulus)

The distribution and spread of hop latent viroid (HLVd) in two adjacent plantings of the hop cultivars Omega and Wye Challenger have been studied for three seasons. The planting of cv. Omega was heavily infected at the start of the survey and spread was rapid; the density of infection was lower in the planting of cv. Wye Challenger and spread was much slower. It is not known whether the difference in rate of spread was a varietal effect or because of the higher density of infection in the Omega planting. The distribution of known infections in 1991 suggests that plant-to-adjacent-plant spread, either by contact or on tools, does occur. However, the overall distribution of infection and the occurrence of new infections not adjacent to existing ones, suggests that this is not the only means of transmission; whether a vector is involved is not known.