The number of viruses that we test for has grown each year of the grant from 8 to 14. A large portion of the collection was woody indexed and we look forward to comparing those results with our lab tests this year. It is apparent from our field trials that it is possible for multiple virus infection to cause young vine failure, but that it is highly dependent on rootstock and virus.
Freedom is particularly sensitive to multiple virus infection.
Approximately half of the plants in one trial died in the second year. Virus symptoms observed on leaves during spring of a Freedom rootstock trial exemplified the fact that virus effects on Freedom are highly variable, ranging from no observable effect to severe stunting, leaf deformation, yellowing, chlorotic line patterns and blotches. Multiple leaf symptoms and low pruning weight are correlated with infection by more than one virus. Three new field trials were planted in 1998. Two are factorial experiments with healthy and virus-infected Cabernet Sauvignon grafted to a panel of rootstocks to observe virus effected on scion and rootstock growth.