Location: Crops Pathology and Genetics Research2013 Annual Report
1a. Objectives (from AD-416):
Assess and extend practical short/near term solutions for decreased water quantity and quality (i.e. soil salinity) issues important to grape growing regions of the Western United States.
1b. Approach (from AD-416):
Assessment of the effect of recommended water and salinity management strategies on quality, sensory, and yield parameters for table, raisin, juice and wine grapes and their commercial products. Development and expansion of commercially available grapevine rootstocks that better resist drought and tolerate salinity. Quantification of the economic sustainability of implementing the strategies in viticulture. Outreach, extension and educational training to disseminate recommendations to grower and academic audiences via presentations, publications, Web-based learning and tailgate outreach. Documents Reimbursable with NIFA.
3. Progress Report:
This agreement was established in support of objective 3 of the in-house project, which is to develop sustainable water management practices for vineyards". As part of this larger project, we have the responsibility of addressing the following two specific project objectives: 1) Develop technologies to quantify real-time remotely accessible measurements of vineyard-scale evapotranspiration and vine water use; and 2) Development and expansion of commercially available grapevine rootstocks that better resist drought and tolerate salinity. Objective 1: This portion of the project aimed to develop an adaptation of the current Surface Renewal (SR) technique that is suitable for monitoring water use in vineyards at commercially viable pricing. This research is progressing very well in the PI’s lab in collaboration with University of California (UC), Davis, collaborators. Our interdisciplinary research team has recently made significant advances in surface renewal technique (the patent is now pending as filed jointly by USDA and UC Davis), which resulted in the elimination of the calibration requirement. This makes routine site-specific evapotranspiration (ET) measurements feasible for commercial agriculture. However, surface renewal ET measurements still require costly, research-grade data acquisition and remote communication platforms, overpriced net radiometers supplied by scientific instrument manufacturers, and highly trained scientists to translate the unprocessed surface renewal data into meaningful ET information. The PhD student funded by this project recently completed his dissertation and is now serving as the post doc on this work. We recently published two additional invited manuscripts from this work. We are also continuing our work in collaboration with another UC Davis scientist at the Thompson Seedless weighing lysimeter site in Parlier to compare results against the water loss estimates from the weighing lysimeters, and have expanded the reach of the project by installing sensors in several additional commercial vineyards. Objective 2: Personnel from the collaborating ARS and UC Davis labs have been working together closely to evaluate rootstock material for abiotic stress resistance. 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 screen 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 suberized cell layers (develop a corky cell layer that limits water movement) under drought conditions)- previous work from Australia also showed that Vitis vinifera grapevines develop higher suberization in fine roots under drought conditions. Working with UC Davis collaborators, the new post doc funded by this grant has started to develop a screen for suberin content of grapevine fine roots using Fourier Transformed Infrared (FTIR) analysis to evaluate the content and quantity of suberin in grapevine rootstocks under well watered and drought conditions. This work has required much effort to develop a baseline of suberin content in various tissues that are being derived from cellular digestions of the fine root materials. This validation will allow us to know definitely what the FTIR spectrum peaks represent in grapevine roots. We are encouraged by preliminary results suggesting that this will develop into a high throughput screen that allows us to see what 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 neutron radiography at the McClellan Nuclear Research Center (UC Davis facility in Sacramento) which allows us to visualize patterns of root water uptake along the length of grapevine roots. We have recently built many replicate chambers to allow for simultaneous comparisons of multiple rootstock accessions under stressed and well- watered conditions. This is being paired with analysis of root architecture from “rhizotron” assays developed by our UC Davis collaborator. We are continuing our efforts to evaluate the effects of drought on embolism formation and repair in living grapevines. To date, we have collected much data on numerous grapevine rootstocks ability to withstand embolism spread and repair these blockages once they occur. In July of 2013, we completed our final set of High Resolution Computed Tomography scans to determine if rootstocks differ in their embolism refilling rates. Additional scans in the summer of 2013 were needed to fill in the the existing dataset and to verify patterns that showed differential rates of refilling among rootstock parent materials. We expect to complete the analysis of this dataset in Fall, 2013, and submit for publication by January, 2014.