Characterization of Grapevine Latent Viruses

We have established that some virus combinations can cause death of young grapevines on some rootstocks. The correlation between the presence of simultaneous infections with GLRV-2 and GVB with latent virus symptoms is striking. This work has been presented as a poster at the June 1999 ASEV meetings in Reno (copy attached). We now have a new hypothesis which we plan to test in future research projects. The hypothesis states that a multiple infection by one of the vitiviruses (GVA, GVB, GVC and GVD) in combination with GLRV-2 can cause vine death or severe decline in some rootstocks. Infection by either a vitivirus or GLRV-2 alone does not appear to have the same severe effect. Extensive RT-PCR testing of the latent virus collection was completed. Grapevine virology and available technology has continued to improve and we are now performing 17 separate tests on the latent virus collection by both PCR and ELISA. Good correlation exists between techniques; at this time each type of test has a contribution to make towards accurate diagnosis. The advantage of RT-PCR testing is that because it is a more sensitive test, we get fewer false negative results. Data obtained from our Freedom rootstock experiments led us to conclude that virus infection by some viruses can be severely deleterious to the growth and health of rootstock; a graft union was not necessary to observe plant decline. In other words, graft incompatiblity does not seem to be the reason for latent virus induced decline. Rather, the degree of rootstock susceptibility determines whether a young vine will decline when infected with certain viruses. We are calling this effect virus-induced rootstock decline. We are in the final stages of collecting and analyzing data from the experiments established under the grant” Characterization of Grapevine Latent Viruses”. We expect to be producing two manuscripts from this work which will be provided to the granting agencies.