This project is to extend the application of a recently developed microtensiometer (MT) device, which measures water tension, to the measurement of stem water potential (SWP) in grapevines under field conditions. The objectives of this project were to test the accuracy of this device using standard laboratory methods, test the performance of sensors compared to pressure chamber measured SWP under field conditions, and help optimize sensor packaging and installation for accuracy and robustness in the field. Laboratory and greenhouse testing indicated that the sensors responded correctly to water potential, although in some cases, sensor response to changes in water potential was relatively slow and temperature sensitivity high, both of which might limit sensor performance in the field. Improvements in the sensor and in handling/installation have been made and are ongoing, but near-commercial prototypes were installed in field vines starting in August, 2018. A total of 14 sensors were installed on 6 mature Cabernet Sauvignon vines in the RMI vineyards at Davis, CA. These vines were minimally drip-irrigated, had not been irrigated for about 3 weeks, and did not receive any irrigation once the sensors were installed. Essentially all sensors exhibited similar daily patterns in SWP that were comparable to patterns shown by the pressure chamber, but there was large sensor-to-sensor variation in the range of water potential values reported. For these vines, the relative values of the sensors indicated that the highest SWP did not occur at predawn (prior to 6:00am in August), as is commonly assumed, but rather about an hour after dawn. The midday minimum water potential (maximum stress) occurred around 3:00 pm, about 2h after peak reference evapotranspiration (ETo). These findings are consistent with previous in-situ measurements in other woody perennial species. Each MT was calibrated against the corresponding pressure chamber measured SWP on an individual vine basis, giving consistent MT measured SWP values for the 5 (of 6) vines in the study that had enough calibration points. The average values from these vines showed a very clear pattern of overnight recovery to about -3 bars from August to November, when rains caused an increase to above -2 bars. Midday SWP values were around -7 bars, also recovering with normal seasonal leaf loss as well as rains. Midday MT measured SWP also fluctuated in parallel with the weather-related baseline (fully irrigated) SWP for about 3 months, indicating the possibility for continuous monitoring over relatively long periods. These data illustrate that automated and sensitive monitoring of SWP in grapevine is possible with these sensors, and should provide useful information for irrigation management as well as for physiological studies.
Considering the importance of the water status as a driver of the whole plant physiology at the vineyard scale, developing new technologies for the space-time measurement of roots distribution and water uptake is crucial for the development of efficient precision viticulture practices. This project (2017-2022) is devoted to the development of a non-invasive technique (electrical resistivity tomography, ERT), as a tool to compare dynamic changes in root growth and water uptake patterns, and to apply this technique to the study of several commercially available rootstocks under varied irrigation delivery methods (drippers, micro-sprinklers) and water regimes (sustained deficit irrigation, rain fed, fully watered). The project was conducted in a vineyard at UC Davis specifically planted for the study of the response of rootstocks to watering systems. According to the timetable of the funded proposal the first year consisted of two parallel objectives: i) the calibration of ERT to soil water and roots distribution iii) the physiological monitoring of different rootstocks under different water amounts and delivery methods.
In a vineyard planted to Chardonnay on different rootstocks representing the most common parentage classes in a randomized complete block design, six soil pits were dug for the description of the soil profile, the sampling of the soil for chemical-physical analysis and the installation of TDR probes for the monitoring of soil moisture. The pits were then refilled, and the soil allowed to resettle for several months before the measurements commenced. The section of the field used for calibration purposes was not irrigated throughout the season in order to cover a full range of moisture levels for that soil (from 24% to 8% vol.). In close correspondence of these pits, at the soil surface 300 stainless steel electrodes were installed at a distance of 0.62 m (2 feet) for the ERT monitoring. A single ERT measurement was able to cover 2 plants on 2 different rootstock, which represented an experimental unit. The water status of the plants within the experimental units was monitored using infrared thermography and pressure chamber measurements. Photosynthesis and stomatal conductance were monitored through a pressure bomb. The electrical resistivity was calibrated to the soil water content obtained by TDR measurements, and two different pedoelectrical models were fitted to the data: Archie, in a canonical and linearized form, and Waxman and Smits models. Their performances were tested on 20% of the data from the whole dataset that were excluded from the model fitting and then used as a test set of unobserved data. The three modeling approaches gave similar results on the test set, with a slight decrease in performance from the log-log linearization (RMSE = 1.22% vol., R2 = 0.73) and the Archie law (1.22 %vol., R2 = 0.73), to the Waxman-Smits model (RMSE = 1.23% vol., R2 = 0.73). The Archie law was then chosen, and confirmed to be well adapted to predominantly sandy soils such as the experiment site. This calibration was used to transform the ERT images from soil resistivity to soil moisture maps under different rootstocks in 2D and 3D. This is the first report in the world that 3D images of soil moisture were developed in a vineyard, and the first time that this technique was used to compare rootstock physiology in general. Great differences were found between contiguous rootstocks in their spatial use of water. The presented data show how lateral heterogeneity in soil moisture could reduce the efficiency of spot measurements, as those obtained with soil probes, and soil moisture sensors in determining irrigation needs.
At the end of the season, the soil was sampled with an auger at different locations in the middle between contiguous ERT electrodes. The soil was sampled every 0.1 m, brought to the laboratory and oven-dried. Roots were physically separated from the soil, and their presence was assessed in a gravimetrically (mg of roots per g of soil). The presence of roots was negatively correlated to soil moisture obtained through ERT (r = 0.45), i.e. greater the amount of roots, lower the amount of water at the end of a dry period. This relations was then used to map the roots using ERT as ancillary variable for the spatialization, therefore developing the first electrical image of root distribution in a vineyard.
Auxin-Response Factors (ARFs) together with Aux/IAA proteins mediate auxin responses including, floral development, fertilization, fruit set and development, and ripening process1. Among them, from our past research, the auxin response factor 4, VviARF4 a likely “key genetic regulator” during the onset of ripening2. The research project is proposed 1) to characterize the function of VviARF4 through genetic engineering, and to identify potential regulatory protein partners of ARF4* (see comments at the end of the document), 2) to determine the ripening-related genes targeted by VviARF4 during the onset of ripening, and 3) to evaluate the impact of altered expression of VviARF4 on the final fruit composition.
Since the commencement of the project in June 2016, significant efforts were made towards the objective 1. We first finalized the agreement for shipping the microvine lines with the USDA (See supplemental data). The signature of the Material Transfer Agreement is on its way between OSU and the CSIRO. Meanwhile, we concluded the logistics of the complex cloning strategies and finalized several vector constructs to transform the microvines designed to either turn on or turn off the activity of VviARF4 specifically during the fruit maturation stage. In the preliminary experiments, we are testing the gene silencing strategy in strawberry (Fragaria ananasa), which shows similar developmental pattern of ARF4 expression during the ripening initiation stage. The plasmid vectors designed to silence the endogenous FaARF4 and to over express the ARF4 from grapevine will into an aggressive Agrobacterium bacterium strain (EHA105). We plan the transient transformation experiments in strawberry within three weeks from now. This will help to establish the role of ARF4 in another non-climacteric fruit model and will enable us to optimize our cloning strategy for the microvines.
The second part of the objective 1 is to find the regulatory protein partners of VviARF4 for which, we initiated the Yeast Two Hybrid Screens (Y2H). Through this approach, we expect to identify potential protein partners of VviARF4, which could have major regulatory role in VviARF4 gene function during the ripening initiation stage. We concluded the experiments to estimate the efficiency of library transformation in yeast and obtained satisfactory results. We are now preparing the final library in order to find the protein candidates that interact with ARF4.
Finally, as part of the objective 3, we are currently building our library of primary and secondary metabolites that will be analyzed when the microvines are transformed during the second year. The shipping of the microvines is expected by mid-February. Meanwhile, we are preparing the various media necessary to maintain the microvine calluses, to induce embryogenesis, to promote the regeneration, and to propagate the transformed materials. We anticipate being ready with the gene constructs cloned in to the Plant Gene Switch Vector to over-and under-express ARF4 before the microvine materials from CISRO, Australia arrive. The post-doctoral researcher is scheduled to fly to Australia in late March to get trained for the critical steps of the microvine transformation in collaboration with Dr. Thomas.
Grape growers are in need of improved precision irrigation management tools that are cost effective and low labor intensive to manage both irrigation amount and timing of their crops. Multiple experiments were carried out to find alternative methods to measure grape water stress that could be couple with water use estimates obtained from surface renewal stations. These methods ranged from using single point IRT temperature measurements to fully automated station that measured surface temperature in real time. The primary objective of this year’s experiments was to determine if stress indices derived from less labor intensive methods such using VSIM and IRT models could be used as a replacement to the more costly and labor intensive commonly used by growers at this time.
Experiments were carried out in three locations. Ten surface renewal stations measured grape water use and water stress in J. Lohr vineyards located in Paso Robles. Leaf water potential measurements were made along with single point IRT canopy temperature measurements using a handheld IRT sensor. Stress indices derived from the handheld IRT temperature values had inconsistent degrees of relationship strength from one site to the next, when compared to leaf water potential values. There was no single stress index, IRT or surface renewal derived, that performed consistently better than the others across all sites. Two stationary stations measured continuous canopy temperature measurements on J. Lohr sites 11-2 and 1-2. Micrometeorological data was collected from reference evapotranspiration stations set up nearby. Stress indices derived from these two stations had strong relationships with the leaf water potential values that were measured.
Two more stationary stations making continual IRT surface temperature measurements were set up in collaboration with Terlato Wine Group over vineyards in the Napa and Pope valleys. Micrometeorological data collected from nearby weather stations were used along with the IRT surface temperatures to calculate stress indices. These stress indices had strong relationships with leaf water potential measurements.
A weather station was set up in the UC Davis Tyree teaching vineyard equipped with sensors to measure canopy temperature, windspeed, air temperature, incoming solar radiation, and relative humidity. Sensible heat flux values calculated using IRT surface temperatures and the surface renewal method had a strong relationship with sensible heat flux values calculated from eddy covariance. Canopy stomatal conductance calculated using IRT canopy temperature measurements had a strong relationship with leaf stomatal conductance values measured with a porometer and stress indices also showed high correlation with leaf water potential measurements made on the Cabernet grape vines.
With our first year of funding from CGRIC, we made significant progress on this project and exciting new discoveries about grapevine fine root responses to drought that shed light on the differences among genotypes/rootstocks. The start date of the project was delayed by ~12months while we waited for the funds to become available, thus we couldn’t justify submitting a renewal in January 2016 for additional funds. We are now submitting a renewal to continue these efforts, which will cover the costs for the second year of the project. Our labs are continuing to work together closely on this and other related projects. In addition to the experimental results described below, we have collected and begun analyzing suberin responses using flurol yellow staining for the following 16 rootstocks/genotypes from a drought experiment run by Dr. Kevin Fort (Walker Lab)
This research focuses on the adaptation and drought responses in yield and fruit and wine quality of seventeen, red wine grape cultivars. The project exploits an established variety trial in which the cultivars were selected for potential adaptation to San Joaquin Valley conditions and by doing so extend the information derived from the previous investment to establish this experimental vineyard – used by Dr. Jim Wolpert from 2006 to 2010. Reducing the plant-available water (by restricting irrigation) can be expected to reduce yield, but to also increase water use efficiency and fruit quality of red wine grapes. The timing of water deficits affects many of the vine responses to stress and the resulting wine sensory characteristics. For example, early(preveraison) deficits have a greater effect on tannins than late deficits, whereas for anthocyanins(color) it is the reverse. The studies that have established these phenomena were conducted in moderate (North Coast) climates and with common cultivars such as Merlot, Cabernet Sauvignon and Cabernet franc. This study will test whether those observations hold in the warmer San Joaquin Valley across numerous cultivars.
Estimated ETc from budbreak to average date of harvest across cultivars and irrigation treatments (end of August) was 619 mm (24.4 in). Applied water to vines irrigated at full ET from budbreak to veraison after which the irrigation was terminated (I ? Ni treatment), applied water at 50%of estimated ETc season long (0.5 ETc treatment) and no applied water up to veraison and then applications thereafter at 50%of ETc (Ni ? 0.5) were 397, 347 – 453 and 173 – 293 mm, respectively. The effect of irrigation treatment on vine water status (midday leaf water potential) similarly affected all cultivars.
Early water deficits (no applied water up to veraison; Ni ? 0.5 treatment) greatly reduced berry weight at veraison and harvest compared to the other two irrigation treatments across cultivars. The no applied water after veraison treatment (I ? Ni) reduced berry weight of 13 cultivars at harvest compared to their veraison berry weight. Titratable acidity (TA) in the berries of 15 of the cultivars at harvest was greater for the I ? Ni treatment compared to the other two irrigation treatments (the exceptions were Tinta Amarella and Tinta Madeira). The greatest TA values across irrigation treatments were for Durif, Cabernet Sauvignon and Tannat. Berries and the wines made last year are currently being analyzed for color, phenols and tannins.
Deficit irrigation has evolved as a tool to reduce water use in viticulture because of increasing water scarcity in many agricultural regions. The accomplishment of this objective depends on the accurate knowledge of both vineyard water requirements and vine water status. The improved surface renewal method (SR) is a bio-meteorological technique that can be used to accurately measure crop evapotranspiration (ETa) at a vineyard scale. A deficit irrigation experiment was carried out in a commercial vineyard of the North Coast Viticultural Region, CA.
The objective of the study was to determine the impact of irrigation practices on the relationships of SR estimates of ETa and vine water status parameters, such as leaf water potential (ΨLEAF) and stomatal conductance (gs). Three irrigation treatments were applied from veraison to harvest: Wet Control: vines were irrigated at 100%ETc (as calculated by Williams & Ayars, 2005); Medium-Wet: vines were irrigated between 70-80%ETc; Moderate Deficit: vines were irrigated between 40-50%ETc. SR provided with reliable estimates of daily ETa compared to the eddy covariance, which is regarded as the reference bio-meteorological method for measuring ETa.
Although ΨLEAF was consistently higher in the wet control than in medium-wet and moderate deficit treatments, the medium-wet block showed the highest ETa and gs values. Surprisingly, vines from the wet and the moderate deficit treatments often exhibited similar ETa values, regardless of large differences in applied water and ΨLEAF. A quadratic relationship between ETa/ETo and ΨLEAF indicated that the maximum water demand was reached at mild levels of water stress (~0.9 MPa). Conversely, vines under wet (>-0.7 MPa) or severe water stress (<-1.4 MPa) conditions showed similar ETa/ETo values. These results showed that the SR technique can be used to better understand the extent of the effect of irrigation practices on both vineyard water use and vine water status in winegrape production.
Deficit irrigation has evolved as a tool to reduce water use in viticulture because of increasing water scarcity in many agricultural regions. The accomplishment of this objective depends on the accurate knowledge of both vineyard water requirements and vine water status. The improved surface renewal method (SR) is a bio-meteorological technique that can be used to accurately measure crop evapotranspiration (ETa) at a vineyard scale. A deficit irrigation experiment was carried out in a commercial vineyard of the North Coast Viticultural Region, CA. The objective of the study was to determine the impact of irrigation practices on the relationships of SR estimates of ETa and vine water status parameters, such as leaf water potential (ΨLEAF) and stomatal conductance (gs). Three irrigation treatments were applied from veraison to harvest: Wet Control: vines were irrigated at 100%ETc (as calculated by Williams & Ayars, 2005); Medium-Wet: vines were irrigated between 70-80%ETc; Moderate Deficit: vines were irrigated between 40-50%ETc. SR provided with reliable estimates of daily ETa compared to the eddy covariance, which is regarded as the reference bio-meteorological method for measuring ETa. Although ΨLEAF was consistently higher in the wet control than in medium-wet and moderate deficit treatments, the medium-wet block showed the highest ETa and gs values. Surprisingly, vines from the wet and the moderate deficit treatments often exhibited similar ETa values, regardless of large differences in applied water and ΨLEAF. A quadratic relationship between ETa/ETo and ΨLEAF indicated that the maximum water demand was reached at mild levels of water stress (~0.9 MPa). Conversely, vines under wet (>-0.7 MPa) or severe water stress (<-1.4 MPa) conditions showed similar ETa/ETo values. These results showed that the SR technique can be used to better understand the extent of the effect of irrigation practices on both vineyard water use and vine water status in winegrape production.
Field experiments were implemented in the 2010 season to contrast the impact of varied deficit irrigation regimes on vine development and fruit composition in Tempranillo and Cabernet Sauvignon. A similar randomized split-plot design was imposed at each site with three treatment replicates. Soil textures range from deep gravelly loam (> 5 feet) to silty clay loam soils (< 3 feet). The late winter and early spring weather conditions across the Southern Oregon region required some adjustment in the original irrigation protocols. Initiation of irrigation was delayed due to the cool and wet soil conditions. Based on the site specific weekly ETo and canopy width, each cooperator maintained the following irrigation treatments: (SD-35) initiate irrigation at 35 percent of ETc for the entire season; (RDI-35) initiate irrigation at 35 percent ETc until veraison, then 70 percent ETc until harvest; (SD-70) initiate irrigation at 70 percent ETc until harvest; and (RDI-75) initiate irrigation at 70 percent ETc until veraison, then 35 percent ETc to harvest. Fruit chemistry analysis continues at the time of this report in collaboration with the Dept. of Chemistry at Southern Oregon University. All members of this project agree that the atypical weather conditions in 2010 were an important factor having strong influence on the development and degree of water stress imposed in all treatments. Irrigation and crop level adjustments had variable impacts on leaf water potential, yield, Brix, pH, titratable acidity (TA), and leaf nutrition. Deficit irrigation treatments had a greater impact on Tempranillo in contrast to Cabernet. Irrigation and thinning had impact on fruit chemistry and ripening early, but by harvest these effects were muted and more variable. Beyond differences due to site, differences in crop level had greater, though variable impacts on fruit chemistry at intervals closer to veraison than harvest. At harvest there were few significant differences in Brix, pH, and TA due to irrigation, crop level, or the interaction of the two. Crop thinning generally had a greater impact on Brix (higher) closer to veraison than at harvest. Sugar accumulation was greatest in earlier ripening Tempranillo in comparison to the very late (under 2010 conditions) Cabernet crops at both sites. Acidity measures were also higher in Cabernet at harvest, and generally the deep soil site that produced both Tempranillo and Cabernet had lower fruit acidity than the shallow soil sites from 2 weeks post-veraison to harvest. Preliminary analyses surprisingly suggest that berry weight may have been greater in 35 percent deficit treatments, and greater in RDI treatments in contrast to SD treatments. Irrigation had a significant effect on many vine nutrients, although Tempranillo and Cabernet responded differently. Higher concentrations of N and other macronutrients in Tempranillo leaves from 35 percent deficit irrigation treatments may not be entirely due to growth or vigor ?dilution? effects. In contrast Cabernet often had higher macronutrient concentration with 75 percent deficit irrigation. We are still amassing and analyzing data to further our interpretation of 2010 experiments and will have a comprehensive final project report this spring.
Weighing lysimeters are the standard for crop evapotranspiration (ETc) measurements. A large weighing lysimeter at the Kearney Agricultural Center has been successfully used since 1987 to measure water use of Thompson Seedless grapevines during vineyard establishment and once the vines were mature. While weighing lysimeters will provide a direct measure of grapevine water use, they are expensive to build and much time is needed to ensure their measurements are accurate. An alternative, allowing the accurate measurement of many vines at one time and highly portable, would be useful in viticulture. One such technique would be the use of sap flow sensors, which have been used to measure transpiration of young and mature grapevines. In this study we further developed and implemented a newly modified sap flow technique capable of precisely measuring both high and low rates of grapevine transpiration. The compensation heat pulse method (CHPM), which has been shown to work well under high flow rate conditions, and the heat ratio method (HRM), shown to work well under low and reverse flow conditions, were used to measure sap flow in this study. These sensors were installed in the trunks of the vines in the lysimeter and on several vines growing outside the lysimeter. Sap flow velocity was converted into water volume per hour by obtaining an estimate of the cross-sectional area of the trunk?s xylem active in the transport of water. Heat pulse techniques closely tracked diurnal grapevine water use determined through lysimetry in both the 2008 and 2009 growing season. This was true even at very high flow rates (> 6 Lvine-1 h-1) under which these techniques had not been previously tested in grapevines where measurements are more prone to error and errors would have the greatest effect on cumulative measurements. Volumetric water use determined with heat pulse techniques was highly correlated to hourly lysimeter water use both years, but the nature of the relationship was inconsistent from one year to the next (y = 0.45 + 0.33x; R2 = 0.92 in 2008, y = -1.00 + 1.47x; R2 = 0.95 in 2009). Similar results were obtained when comparing grapevine water use determined from heat pulse techniques to meteorological estimates for field-grown vines in Napa Valley and Davis and to bench scale lysimetry of two year-old potted vines grown in a greenhouse. The inconsistency in the regression coefficients obtained from each of these data sets was likely due to radial and circumferential variation in sap flow through the vines? trunks. However, the robust nature of all of the correlations demonstrates that heat pulse techniques can be used to measure grapevine water use after an in situ calibration. Conversely, the data from the sensors could be utilized as a measure of vine water status, similar to that of a pressure chamber used to measure leaf water potential. Once a critical value had been measured, such a baseline, maximum daily heat pulse velocity (or relative heat pulse velocity), one would schedule an irrigation event. Such an example is given in Figure 2, where daily heat pulse velocity decreases due to the termination of irrigation. However, like data from a pressure chamber, this technique would not determine how much water to apply.