Xiphinema index and Grape Fanleaf Virus Disease Complex: Defining Nematode
We have initiated experiments using large soil containers (4′ X 5′ X 5′) containing a coarse sand:clay mix. The containers were selected to allow us to simulate field conditions, with controlled soil conditions. The containers were planted in the spring of 1996 with the highly susceptible Rupestris St. George rootstock, to allow nematode (Xiphinema index) populations to increase. The plants were inoculated with Grape Fanleaf Virus (GFLV) with or without X. index during summer of 1996. Our objective is to determine how X. index and GFLV, separately and together, influence nematode population dynamics, virus prevalence, and plant growth and yield relative to rootstock. Upon sampling the units during late summer of 1997, we observed all nematode stages, (juveniles to adults), in all containers save one, indicating nematode reproduction. In addition, we observed nematode feeding damage on the roots, with large terminal galls at root termini. We counted nematode numbers in each experimental treatment, and interestingly, the nematode densities in the nematode and GFLV treatment were significantly lower than where the virus was absent. Although this is preliminary data, it suggests a previously undocumented interaction between the nematode and the virus, and that the presence of the virus reduces nematode reproduction. It is possible that this is due to a general decline in vine vigor due to the combined influence of the nematode and the virus. This research is continuing, and we should be able to ascertain details of the interaction between virus and nematode through more intensive sampling. In late spring of 1998 we move into the next phase of the experiments, and will introduce a resistant rootstock to half of the experimental units, so that we can document the influence of resistance on nematode dynamics, virus transmission and prevalence, and plant growth and yield.