Characterization of Grapevine Latent Viruses
Significant progress has been made in virus detection in the latent virus collection with the addition of RT-PCR testing and availability of 3 new ELISA tests. The number of viruses that we test for has grown each year of the grant from 8 to 14. This was the first year the collection was tested for GVB, GVC, RSP, and GFkV. We have found that most of the collection is infected with multiple viruses; as many as 7 viruses were detected in some samples. 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. The third is a trial of Freedom rootstock to which 19 virus sources were inoculated to observe virus effects on rootstock growth and symptom development. We have collected baseline data from these trials and will be observing and collecting data over the next seasons.