2012 Annual Report
1a.Objectives (from AD-416):
1. Investigate leaf anatomy and morphology of well-watered and water-stressed grapevines using light and electron microscopy.
2. Monitor berry ripening and fruit quality characteristics of well watered and water stressed grapevines.
1b.Approach (from AD-416):
Research will be conducted on two cultivars in a greenhouse and drought conditions will be simulated. Leaves will be tagged on the vines of both cultivars to determine leaf age. During the dry-down and re-watering cycles, the physiological, anatomical, and morphological characteristics will be measured in both cultivars to assess drought resistance. Prior to sampling tissues for all microscopy studies, photosynthesis, dark respiration, and stomatal conductance will be measured on leaves of well-watered and water-stressed grapevines. Fruit quality characteristics such as Brix, pH, titratable acidity, color etc., will be measured to examine ripening behavior and quality characteristics during dry-down and re-watering cycles.
This research was conducted in support of objective 305 1B Perennial Crops. Based on the results and analysis, from physiological aspects, Zinfandel showed the highest stomatal conductance under well watered conditions and mild water stress conditions, however, its stomatal conductance decreased to the same level as Grenache and Cabernet, indicating its stomatal behavior changes quickly in response to water stress. Leaf water potential showed that Grenache had high water potential than Zinfandel and Cabernet Sauvignon indicating it has the ability to remain “tough” under water stress. Grenache showed higher RWC than Zinfandel and Cabernet Sauvignon. Therefore, compared to Zinfandel, Grenache showed a more stable stomatal behavior, less negative midday leaf water potential and high relative water content indicating it is more drought resistant than Zinfandel from physiological aspects. In all three cultivars, the physiology was altered in response to water stress, especially under severe water stress conditions. However, no treatment effects were found in RWC indicating its low sensitivity to water stress. A similar pattern was observed for wax load.
From morphological and anatomical aspect, severe water stress reduced leaf size. Zinfandel showed higher leaf size than Grenache. For leaf thickness, with increasing water stress, Grenache increased leaf thickness to reduce surface to volume which is a positive strategy to resist drought. Water stress reduced stomatal pore areas significantly but not stomatal density. Palisade cell length of Zinfandel was very responsive to water stress while Grenache showed longer palisade cell length under water stress. Also, water stress affected intercellular air spaces of the three cultivars with Grenache showing the highest values. Water stress did cause differences in their morphology and anatomy except leaf vein density of Zinfandel and Grenache. Cavitation occurred under the severe water stressed treatment of the three cultivars showing all of them were vulnerable to water-stress induced cavitation. Water stress in general altered the fruit composition; however, more research using different stress levels is needed to better understand the water stress effect on fruit composition. Among the three, Grenache performed the best followed by Cabernet Sauvignon and Zinfandel in terms of grapevine physiology, morphology and anatomy.
Based on this study, Grenache was very adaptive to drought conditions. Thus, its resilience can be exploited to make planting recommendations in sites with limited availability of water. The information gathered from this study can be useful for guiding targeted irrigation strategies, which focus on delivering water to the grapevines only when it is necessary in established vineyards. Furthermore, the results of this research will assist vineyard managers to manage water efficiently in planted vineyards by targeting cultivars that show resilience to drought. Such approaches have the potential to improve crop quality while at the same time reducing water use. For new growers, the information will help them guide vineyard design and subsequent development. Additionally, this research has potential benefits to environment which include improvement in biodiversity and air quality (dust control), reduction in land degradation and improvement in productive capacity of the land, and finally having such land planted with grapevines contributes to visual (aesthetic) and landscape qualities.