A Genetic Map of Vitis vinifera: A Foundation for Improving the Management of
The goal of this project is to develop a basic genome map for grape (Vitis vinifera) that will allow us to begin to locate the genes that control important viticultural and enological characteristics, such as disease resistance and fruit composition. This will not only allow us to ultimately move these genes from one variety to another, whether by traditional or biotechnological means, but it will also facilitate the study of how these genes work and how they are affected by environmental and cultural conditions. The development of a genome map requires a population of progeny individuals derived from a cross between two disparate parents. We have used Cabernet Sauvignon and Riesling, two quite different wine grape cultivars, and have a population of 116 seedling vines derived from this cross that is now 4 years old. We have now obtained 178 DNA “markers” that we are placing in positions along the different grape chromosomes. The DNA markers are like signposts along a road. We have located some of these markers on specific chromosomes but others are not yet assigned to a chromosome. Cluster structure (e.g., compactness) is among the many characteristics that are under genetic control. Tight clusters are prone to rot. Loose clusters tend to have smaller berries, which are often preferable for winemaking. It is likely that many genes are involved in determining cluster structure. Some may determine the number of flowers that form on a cluster; others may determine the maximum berry size; and others may determine the length of the pedicel or the branching pattern of the rachis. We are trying to sort out these various components of cluster structure, to determine how many genes control them and to find the genome location for these genes. We are collecting data on 9 berry and cluster characteristics from all of our seedling vines in our mapping population but, because the vines are still quite young, we have only 1 year of data and will need several more before we can begin to interpret this data. Most of the DNA markers that we have been using for our genome map are of the type called AFLP markers. It is relatively easy to generate large numbers of these markers, but they have some limitations and information gained with these markers cannot always be shared with other researchers who are working with different mapping populations. Microsatellite markers, on the other hand, are more powerful and can be used on any mapping population. Unfortunately, these markers are much harder to come by and their discovery and development is very laborious. In order to obtain a large number of microsatellite markers, we have formed an international Vitis Microsatellite Consortium in which researchers in several countries will share in the effort to develop new grape microsatellite markers and will then share in the benefits. After about 10 months of correspondence, organization and the negotiation of a written agreement, the consortium is now underway and up to 20 grape research groups in 10 countries are expected to ultimately join in the effort.