Location: Crops Pathology and Genetics Research2011 Annual Report
1a. Objectives (from AD-416)
1. Develop sustainable disease control practices for grapevines. 2. Develop sustainable vineyard floor management practices. 3. Develop sustainable water management practices for vineyards. 4. Investigate the impacts of vineyard practices on soil microbial ecology. 5. Identify & characterize viral & graft-transmissable agents of grapevine.
1b. Approach (from AD-416)
1. Characterize the infection process of grapevine roots by the fungal pathogen Armillaria mellea, the causal agent of Armillaria root disease; Characterize the significance of riparian areas in the spread of Pierce's disease; and Identify and characterize viral and graft transmissible agents. 2. Identify differences in regional populations of Conyza canadensis, cover crops that effectively compete with c. canadensis, and effects of soil resource availability on competition between cover crops and C. canadensis; and Identify cover crops that effectively compete with problematic weeds. 3. Evaluate the interactive effects of irrigation practices and vineyard floor management practices on grapevine yield, growth, physiology, and nutrition. 4. Examine the effect of cover crop functional type on soil microbial communities and microbially-mediated soil processes; Characterize rhizosphere communities associated with Vitis rootstocks; and examine the impacts of vineyard floor practices on mycorrhizae.
3. Progress Report
Our research on sustainable vineyard production systems in FY2011 yielded several applications to the practice of viticulture and also produced basic findings for the scientific community. As a multi-disciplinary team, our continued commitment to integrating research on disease and weed management, soil and nutrition management, and irrigation was exemplified by several accomplishments. First, we demonstrated that the planting of no-till cover crops in between the vineyard rows did not bring about the types of negative impacts on the nitrogen chemistry of the grapes that have been suspected by winemakers for yeard. Such empirical evidence is an important step in convincing growers to adopt more sustainable management practices for the vineyard floor. Second, we developed technologies for accurate and precise measurement of water use in the grapevine. Water use is and will forever be an important priority for our Nation’s farmers, and this work gives growers the tools they need to decide when and how much to irrigate. Third, we were awarded a planning grant from the USDA-NIFA Specialty Crop Research Initiative for research on trunk diseases of grape, stone fruits, and nut crops. This planning grant is a new opportunity for us to develop collaborative projects with researchers from divergent disciplines and different cropping systems, in an effort to make significant strides in the control of trunk pathogens that significantly restrict the life of vineyards and orchards throughout the US.
1. Genetic transformation of the honey mushroom makes it possible to reliably re-create a novel mode of reproduction known only to the Fungal Kingdom. Armillaria root disease is one of the most damaging diseases of grapevines, stonefruits, and nut trees in the world. The reproductive modes of the causal fungus Armillaria mellea (a.k.a. honey mushroom) are not all known, and the absence of this information the development of effective controls for the disease. Researchers in the Crops Pathology/Genetics Research Unit in Davis, CA, developed the first genetic transformation system for the fungus, which they used to identify a reproductive mode unique to Fungi, somatic recombination. Prior to this work, there was indirect evidence of somatic recombination in nature, and this work makes it possible to determine if strains that have undergone somatic recombination are more aggressive in attacking the roots of plants than are typical strains. Researchers can now use this information about reproduction of the fungus to identify the most aggressive strains of the fungus for identifying resistant plants, which is a biologically-based strategy that is needed by fruit and nut crop-growers as an alternative to the soil fumigant methyl-bromide.
2. Cover crops and no-till strategies enhance soil quality, but do not influence nitrogen compound composition in the vineyard. Switching to no-till practices can reduce greenhouse gas emissions due to a decrease in tractor fuel use, and cover crops enhance soil organic matter. However, grape-growers are hesitant to adopt such practices because they can in some cases negatively impact the chemistry of the grape and, in turn, the characteristics of the resulting wine. When Cabernet-Sauvignon was grown in a cover-cropped vineyard and/or with no-till vs. tilled soils, no detrimental effects of these management practices were detected in grape nitrogen content, amino acid composition, or organic acids. Therefore, a no-till management strategy is a sustainable practice, and is an alternative to tilling that does not negatively affect grape chemistry. There were differences among rootstocks, and so further work linking grape nitrogen compounds to specific wine volatile characteristics may give winemakers the ability to manipulate nitrogen concentrations in the grapes by selecting specific rootstocks.
3. Grapevine rootstock hydraulic physiology. Water scarcity threatens crop production in dry growing regions of the western US. Reduced water availability will force growers to use conservation techniques (e.g. deficit irrigation or dry-farming) while attempting to maintain yields. To take full advantage of these strategies, growers require plant material that can tolerate drier growing conditions. The goal of this work was to identify inherent characteristics that distinguish grapevine rootstocks in terms of drought resistance and vigor. ARS scientists in Davis, CA, discovered that gene expression of aquaporins (water-specific protein channels found in plant cell membranes) was found to be significantly higher in high-vigor and drought-resistant grapevine rootstocks, compared to those with low vigor and drought intolerance. Through an on-going collaboration with a breeder, the knowledge generated here will facilitate screening of grapevine rootstocks from species native to harsh growing conditions of the arid southwestern US.
4. Screening plant material to identify hydraulic characteristics. Decreased water quantity and quality issues are important to grape growing regions of the Western United States. ARS scientists used High Resolution Computed Tomography (HRCT, a type of CAT scan) to view the inner workings of grapevine vasculature with a goal of better understanding drought and disease resistance. We developed a custom software package called PHAST (Physiologically-based High-speed Automated Software Technique) that automatically extracts dimensions and the distribution of connections from HRCT scans of grapevine xylem – the water conducting tissue of plants. PHAST was applied to scans of two grapevine species. The PHAST software and methodology is a new tool for applied screening of plant material to identify hydraulic characteristics that impart resistance to abiotic and biotic stress.
5. Improved accessibility to energy and flux measurements. Ecosystem-scale energy and gas flux measurements have become increasingly important in soil, crop, and environmental sciences, but for many scientists without formal training in atmospheric science, these techniques are relatively inaccessible. In collaboration with UC Davis researchers, ARS scientists in Davis, CA, developed a new tool (an open-source turnkey data logger program that performs flux data acquisition and post-processing) to improve access to flux measurement methods for agricultural and environmental research scientists. The new program returns to the user a simple data table with the corrected fluxes and quality control parameters; previously researchers had to shuttle between multiple processing programs to obtain the final flux data. Different versions of the program are available to meet various research needs and instrumentation configurations. The programs have already been deployed in numerous field experiments for the UC Davis Atmospheric Science Dept and the CA Dept of Water Resources in the following crops: rice, wine and raisin grape vineyards, alfalfa, almond, walnut, peach, lemon, avocado, and corn.
Baumgartner, K., Foster, G.D., Bailey, A.M. 2010. Agrobacterium-mediated transformation for the investigation of somatic recombination in the fungal pathogen Armillaria. Applied and Environmental Microbiology. 76:7990-7996.