Location: Water Management Research2013 Annual Report
1a. Objectives (from AD-416):
Access currently available, newly released, and new parent rootstock materials for their physiological responses and tolerance to soil salinity and/or drought under greenhouse and field conditions. Quantify the effects of salinity and/or drought on scion physiological performance in terms of vine water relations, gas exhange, vine mineral nutrition, fruit yield, and quality under field and lab conditions.
1b. Approach (from AD-416):
The research will be a combination of field studies on cooperating farms, laboratory studies at UC Davis, greenhouse studies and sand tank studies at U.S. Salinity Laboratory.
3. Progress Report:
This project contributes to meeting objective 2 “Develop sustainable water management strategies for perennial horticultural crops with limited and impaired water supplies” of the parent project. This project is evaluating rootstocks for both drought and salt tolerance which will be required in situations with limited and impaired water for irrigation. Personnel from an ARS lab at UC Davis and a UC Davis laboratory have been working together closely to evaluate rootstock material for abiotic stress resistance. The ARS lab personnel are focused primarily on drought resistance aspects of grapevine rootstocks. Drought resistance in a cropping system can be defined as the ability of a plant to continue growth and maintain yield and fruit quality when exposed to periods of water stress. For grapevines it is suspected that the following rootstock traits are important in imparting drought resistance to a vine: 1) large & active root system; 2) efficient xylem transport; 3) cavitation resistance/limit embolism formation and spread; 4) embolism repair; 5) high permeability of fine roots; 6) prevent/promote leakage to soil. We have been working to understanding which of these traits (or combination of traits) is relevant to drought resistance in grapevines. Last year we developed a screening technique to evaluate the hydraulic conductivity of fine roots of grapevines. We utilized a variety of rootstocks to perform this analysis and found that fine root hydraulic conductivity was significantly reduced by drought, and responses varied among rootstock genotypes tested. While useful this hydraulic screening is technically challenging and could prove difficult to use during screens of many accessions. To improve on the utility of this screen, we have focused on the chemical and structural changes in fine roots that contribute to the varied hydraulic responses described above. We suspect the drastic reductions in fine root hydraulic conductivity result from the formation of a corky cell layer that limits water movement under drought conditions. Work from Australia has shown that wine grapevines develop higher corky layers in fine roots under drought conditions. Working with UC Davis collaborators, we started to develop a screen for suberin content (corky layer) in grapevine rootstocks under well watered and drought conditions. We are encouraged by preliminary results suggesting that the new screen will develop into a high throughput screen that allows us to see which rootstocks tend to suberize more rapidly than others. This work is being paired with new efforts to better understand patterns of water absorption in grapevine root systems. Grapevines are a woody perennial plant, and as such develop a large woody root system. It is still not known definitely what portions of grapevine root systems actually absorb water. Much of the scientific literature implies that fine root tips are responsible for all water uptake. If this is the case, some of the characteristics that we are evaluating (i.e. large and extensive root systems, which will consist predominately of woody roots) may not actually reflect functional consequences/patterns of actual water use by root systems. We are now exploring how much and what portion of a given root system is actually absorbing the water and how this differs among rootstocks and under stress conditions. We have initiated efforts to evaluate water absorption in intact root systems using advance imaging techniques that allows us to visualize patterns of root water uptake along the length of grapevine roots. We have built many replicate chambers to allow for simultaneous comparisons of multiple rootstock accessions under stressed and well- watered conditions. This is paired with analysis of root architecture from assays developed by personnel in the UC Davis laboratory. We are continuing our efforts to evaluate the effects of drought on embolism formation and repair in the vascular system of living grapevines. Embolism are blockages that occur in the xylem tissue and prevent movement of water within the plant. To date we have collected much data on numerous grapevine rootstocks ability to withstand embolism spread and repair these blockages once they occur. A data set was completed for root architecture characterizations of all widely-available rootstocks in California. Data were obtained using four weeks of growth in containers with visual access to root development via clear plastic sheet on one side of the container. The results of these studies indicated that the rhizotron containers produced the highest quality data. We used this system to characterize the commercially available rootstocks using sets of six rootstocks at a time and using Riparia Gloire, and Ramsey rootstocks as shallow- and deep-rooting controls, respectively, in each set. A final set of six rootstocks repeated the characterizations for rootstocks that appeared to grow poorly in the first assessment. In all cycles of the assay, we observed consistent responses from the controls. As a first analysis, a rooting depth index was created to provide a single score reflecting root density distribution through the entire rooting profile. Root data were obtained for seven commercial rootstocks following approximately two years of growth in the field. Field data for root architecture was previously considered to be too difficult when characterizing more than a small number of genotypes, however it is critical to characterize at least a representative sample to allow conclusions to be drawn in other systems. We reported the results of a small subsample from this study one year ago with well-watered rootstocks. In the second season, the remaining individuals were divided into well-watered and water-stressed irrigation regimes to follow the same rooting characteristics in more developed plants, and to see if drought significantly altered these traits. Surprisingly, drought had no detectable effect on the most important major rooting characteristic: root angle. This result indicates that root angle has a major genetic determinant that is resistant to environmental variation that might otherwise be expected to alter this architectural trait. The persistence of this character in the field supports our efforts to characterize it in much finer detail under greenhouse conditions where more stocks can be evaluated more rapidly. In this field study, the root angles measured following the second season strongly correlated to those measured following the first season, again illustrating the consistency of this trait. Work in these two laboratories is identifying the traits needed to breed drought resistant rootstocks for use in arid and semi-arid irrigated areas. Additional work is characterizing water uptake by woody roots. This may have a significant impact on future irrigation strategies and irrigation system designs and breeding strategies for rootstocks.