Developing Drought and Salt Resistant Grape Rootstocks

Grape breeders are beginning to consider the consequences of a changing climate and expanding human population. One inescapable conclusion is that there will be less water available for viticulture given the need to produce staple food crops. Summer arid areas like California are ideal for fruit culture, but these soils tend to be more alkaline and prone to problems with salinity, which is controlled by leaching with good quality water. Thus, it seems prudent to expedite the development of grape rootstocks with strong resistance to drought and salinity. Such a breeding program is underway at UC Davis. Modified assays for salt resistance have been developed allowing seedlings to be tested quickly and accurately. We have made extensive collections of Vitis species from across the desert regions of the southwestern United States. Very strong examples of chloride exclusion have been found in accessions of V. acerifolia, V. arizonica, V. berlandieri, V. doaniana and V. girdiana. We are also evaluating the root systems of this region's Vitis species by characterizing root angles, the development of persistent structural roots, and the ability of fibrous roots to regrow after periods of drought. Mapping populations are being generated and phenotyped for the above traits to develop genetic markers for rootstock breeding efforts. Such mapping can also lead to a better understanding of the genes and mechanisms controlling drought and salt resistance. However, these breeding efforts are complicated by a poor understanding of the grape germplasm in the southwestern US, which leads to confusion regarding species characteristics, taxonomy and sources of resistance. Populations of these species exist in or near springs and are widely separated by deserts and mountains. They experience frequent migration events due to the movement of birds carrying seeds up watercourses or between disjunct populations. Consequently, it can be very difficult to define individuals as a given species; more often they appear to be hybrids that intergrade with species on the fringes of their distribution. Our efforts to use landscape and population genetics tools to define these important species and their hybrids will also be discussed.