Location: Crops Pathology and Genetics Research2007 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. REPLACING 5306-21220-003-00D (01/07)
3. Progress Report
With addition of a new SY (McElrone) to the CRIS in FY07, a new emphasis in this program is the development of sustainable water-use for vineyards. Given growing irrigation demands in vineyards, decreasing quantity/quality of freshwater, judicious water management and increased water-use efficiency are crucial. Ultimately, we aim to improve water-use efficiency of vineyard ecosystems through an improved understanding of grapevine water-use dynamics, whole vineyard water balance, and impacts on yield and wine quality. Current and future studies include: (1) evaluating rootstock water transport physiology and stress response (i.e., drought and salt stress), (2) developing sap flow techniques to measure whole vine water use, and (3) assessing the effects of vineyard floor management on grapevine water use. Greenhouse experiments have been initiated using five grapevine rootstocks that exhibit a range of vigor and drought stress tolerance. Water transport physiology, specifically aquaporin activity, is being assessed in the root systems of these plants to determine if these membrane-bound channels contribute to the inherent differences between the rootstocks. Sap flow sensor calibrations have been initiated by instrumenting field-grown grapevines and excised stems in the lab, in order to fine-tune these sensors for measurement of whole vine and root water uptake dynamics. We have also designed a vineyard floor experiment to assess the competitive effects of cover crops on grapevine water-use, and are currently recruiting growers as cooperators on this project. Collectively, this research aims to link irrigation practices more closely with plant demands and water inputs (i.e., precipitation inputs, vapor pressure deficit, and temperature) to develop dynamic systems that maximize irrigation efficiency, and minimize runoff and groundwater contamination. Sustainable disease control is another major emphasis of this project, with basic research on disease epidemiology, infection biology, plant-pathogen interactions, and antagonistic microbes. Our research on inoculum sources, disease spread, and symptom development of Armillaria root disease served as a foundation for our subsequent identification of a cultural practice and a biological treatment. The impact of this research is that growers with diseased vineyards can achieve some level of control, but control of this disease would benefit substantially from a set of resistant rootstocks that accommodate a range of soils. The problem is that we do not have a reliable means of infecting plants in the greenhouse, which is a serious obstacle to identifying resistant plant material, in addition to testing putative biological control agents. In FY07, we developed study tools that allow us to track infection of grapevine rootstocks grown in tissue culture and inoculated with the pathogen, Armillaria mellea, and to distinguish strains of the pathogen. We initiated a similar project with Eutypa lata, the causal agent of Eutypa dieback of grapevine, the study of which is similarly hampered by lack of an efficient inoculation technique.
Identifying Pierce’s disease (PD) risk factors to develop effective pest management techniques. The presence of riparian areas adjacent to North-Coastal California vineyards contributes to PD, as evidenced by a correlation between disease incidence and proximity of vines to riparian areas, but riparian hosts of the pathogen (Xylella fastidiosa) identified solely from greenhouse studies have not been verified by recovery of the pathogen from field plants. The research performed in the USDA, ARS, Crops Pathology/Genetics Research Unit, Davis, CA used a field-based approach to identify riparian hosts correlated with PD. Based on the finding that only one riparian host, Vinca major (periwinkle), was positively correlated with a high incidence of PD in adjacent vineyards, it seems that eradication of all riparian hosts may be unnecessarily costly, not to mention being overly disruptive to riparian ecosystems. Research will aid farmers and administrators in developing effective pest management techniques, particularly, in North Coastal CA Vineyards. This accomplishment supports NP303 Plant Disease; Action Plan Component #4, Biological and Cultural Strategies for Sustainable Disease Management; Action Plan Problem Statement #4B, Pathogen, Plant, and Antagonist Interactions. Understanding influences of soil heterogeneity and grapevine root distribution on soil microbial communities. A Pinot noir vineyard was surveyed to investigate the effect of soil depth and roots on soil microbial communities involved in nutrient turnover and nutrient availability. Soil microbial communities segregated by depth and soil morphology; the gradient in soil resources (e.g., labile carbon) played a primary role in the distribution of soil microbial communities with increasing depth, while soil physical and chemical characteristics played a secondary role. Compared to other systems, the distinct patterns in soil microbial communities as influenced by depth and root distribution in this Pinot noir vineyard suggest that vineyard management practices and the relatively deep distribution of grapevine roots combine to cultivate a unique microbial community among cropping systems. Such shifts in functional groups of soil microbes with increasing soil depth means that the standard vineyard soil/nutrition management practices, which are primarily borrowed from row crop production, require some modification to optimize nutrient turnover and decomposition. This accomplishment supports NP303 Plant Disease; Action Plan Component #4, Biological and Cultural Strategies for Sustainable Disease Management; Action Plan Problem Statement #4A, Biological and Cultural Control Technologies. Effects of cover cropping and tillage on soil biology, and carbon and nitrogen cycling in vineyards. Carbon (C) and nitrogen (N) dynamics were monitored in non-cover-cropped soil versus cover-cropped soil of a Chardonnay vineyard in California’s Central Coast, as one component of a five-year project aimed at developing sustainable vineyard floor management practices. Over the course of two years (2005-2006), both of the cover crop treatments (‘Trios 102’, Triticale x Triticosecale; ‘Merced rye’, Secale cereale) had greater CO2 and N2O efflux, microbial biomass C, ammonium pools, potential rates of nitrification, N mineralization, and denitrification than the non cover-cropped soil. The cover crop treatments shared similar values among these factors, despite differences in their phenology (i.e., germination rate, seedling growth, stature, flowering period). Given that the cover crops clearly enhanced the biological function of the soil, relative to soil that was left to be colonized by weeds, it seems that cover cropping should be included as part of a sustainable vineyard floor management program in Central Coast vineyards of similar soil type. In addition, suppression of early season weed establishment by Merced rye, due to its greater aboveground biomass in late spring compared to Trios 102, suggests that some cover crops have the additional function of weed suppression. Row middles management practices described above had little impact on the nematode populations (quantitive or qualitative) detected in the grape rhizosphere of roots growing in the berm. Similarly, microbial populations in the grape rhizosphere were not statistically impacted by row middle management practices as close as 18 inches away. This accomplishment supports NP303 Plant Disease; Action Plan Component #4, Biological and Cultural Strategies for Sustainable Disease Management; Action Plan Problem Statement #4A, Biological and Cultural Control Technologies. Impacts of in-row soil cultivation for weed control on soil physical properties and soil nitrogen (N) retention. The effects of cultivation and herbicides on N leaching were examined in a Chardonnay vineyard. The two weed management practices, imposed underneath grapevines for five years prior to this study, were: 1) soil cultivation (Clemens cultivator, 4-6 times/year; ‘Cultivated’) and, 2) a combination of pre-emergence and post-emergence herbicides [simazine (2.0 lbs. a.i./A) + oxyflourfen (1.5 lbs. a.i./A) in winter, 2% glyphosate and 25% oxyflourfen in summer; ‘Standard’). In summer, grapevines were fertigated with urea-N mixed with humic acid, then we monitored nitrous oxide (N2O), soil N, and soil moisture for two weeks after fertigation. N2O was greater from the drip zone in Standard than Cultivated during the first three days after fertigation, and leached soil nitrate was ca. 1,200 times greater in Standard than in Cultivated. Grapevine yield was not influenced by either weed management practice. Increased N retention (i.e., reduced leaching) may have been due to the greater weed biomass in Cultivated, suggesting that increased weed biomass underneath grapevines may have the hidden benefit of minimizing fertilizer runoff. This accomplishment supports NP303 Plant Disease; Action Plan Component #4, Biological and Cultural Strategies for Sustainable Disease Management; Action Plan Problem Statement #4A, Biological and Cultural Control Technologies.
5. Significant Activities that Support Special Target Populations