Location: Crops Pathology and Genetics Research2008 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
A continued emphasis in his program is to characterize etiological agents associated with graft union disorders in vineyards, & to develop diagnostic tools to aid in clean plant material programs. Site visits were made to vineyards in several CA counties to diagnose necrotic union related disorders. Necrotic union disorder associated with red leaf disease of Pinot noir clone 4 on rootstock 110R, found previously in Sonoma Co., was also found in Monterey Co. A rootstock trial was established to characterize the new disease collections. A greenhouse study on the problematic vineyard weeds Conyza canadensis & Conyza bonariensis was initiated to determine which physiological tolerances influence herbicide resistance. Several populations of C. canadensis & C. bonariensis from CA's Central Valley were collected & assessed for their physiological tolerance to different germination regimes. Seeds were exposed to all combinations of the following-3 daylengths, 3 osmotic potentials, & 3 temperature regimes. This research is expected to guide herbicide application recommendations in terms of timing & rates. Investigations of impacts of vineyard floor management practices-cover cropping, tillage, and no-till on weed establishment & soil processes were conducted in FY07-08. These investigations were integrated with the study of how these practices influence grapevine growth & physiology. A long-term trial was established in CA’s Central Valley with one of the state’s largest growers. In this study, seasonal changes in weed community composition, net aboveground primary productivity, & associated soil resources occurred. Substantial time & effort was needed to install permanent soil moisture collection tubes to monitor impacts of cover cropping & tillage practices on soil water status, as well as conduct regular measurements for grapevine growth, and nutritional & water status. Employing automated techniques to determine whole field water use was also investigated. The impact of this research will provide a demonstration of the benefits that can be gained from cover cropping, not only for weed establishment but for controlling grapevine growth, influencing grape juice characteristics, and reducing both dust generation & greenhouse gas emissions from fossil fuel use by farming equipment for tillage. To improve water-use efficiency & sustainability in CA vineyards, we initiated research to elucidate the dynamics of grapevine water-use physiology. Continuing greenhouse experiments using potted & hydroponically-grown vines are evaluating rootstock vigor & drought tolerance. Hydraulic physiology & aquaporin activity are being assessed in the rootstocks to determine the relationship between such measurements & salinity tolerance. In another study, vulnerability to drought induced cavitation has been evaluated in vine shoots using air-injection, centrifuge & dry-down techniques. Sap flow sensor design & calibrations are being conducted on excised shoots, potted vines, & mature field-grown vines(growing in a weighing lysimeter) to fine-tune these sensors for measurement of whole vine and root water uptake dynamics. This research addresses NP303, Component 4.
1. First instance of transgene expression in Armillaria, causal agent of Armillaria root disease of grapevine. Armillaria root disease is a problem in vineyards and needs to be better characterized and understood. The Plant Pathology and Genetics Research Unit used particle bombardment to identify promoters for driving transgene expression. The presence of a green dot among A. mellea hyphae bombarded with gold particles coated with plasmid pYES-hph-004iGFP verified that a single cell was penetrated by a particle, and that A. mellea is capable of translating gfp under control of the glyceraldehyde-3-phosphate dehydrogenase (gpdII) promoter from the basidiomycete Agaricus bisporus. Expression was only transient, but this is still an achievement because the gpdII promoter is in plasmids, for both Agrobacterium-mediated and protoplast/PEG mediated transformation, that have been shown to give the highest transformation success among other Basidiomycetes. This accomplishment supports NP303, Component 4, Problem Statement B.
2. Reduced tillage in California vineyards may bring about improvements in air quality, without adversely affecting vine growth. This study’s primary goal is to demonstrate the benefits of reducing the number of tillage passes that occur in the San Joaquin Valley, because dust particles generated by tillage that are less than PM10 contribute to air pollution and are harmful to human respiratory systems. In the Plant Pathology and Genetics Research Unit five vineyard floor treatments (oats + mowing, oats + tillage, oats/legumes +mowing, oats/legumes + tillage, resident vegetation + tillage) were established in November 2007, and weed community composition and associated soil parameters were measured in winter (January, 2008), early spring (February/March, 2008), and late spring (April, 2008). Preliminary results indicate that a cover crop reduces weed biomass and that there are temporal differences in weed community composition among treatments. This is important to understand if specific practices encourage problematic weed species. Grapevine growth parameters and water status are being monitored, and juice parameters will be assessed at harvest. Reduction in the number of tillage passes will reduce both production costs (labor) and environmental costs (greenhouse gas emissions from fossil fuel combustion). This accomplishment supports NP303 Plant Disease, Component 4, Problem Statement A.
3. Cover crops impact vineyard weeds in the interrows of a California vineyard, but not in the intrarows. There is a need to determine whether cover crops adversely affect vine health or weed control in vineyards. In northern California, ARS scientists in the Plant Pathology and genetics Research Unit examined Vineyard weed communities under four dormant season cover crop systems representative of those used in the north-coastal grape-growing region of California: no-till annuals (rose clover, soft brome, zorro fescue), no-till perennials (blue wildrye, California brome, meadow barley, red fescue, yarrow), tilled annual (triticale), and a no cover crop tilled control. The cover crop systems had no effects on weed biomass, community structure, or diversity in the intrarows. The significant effects of the cover crops were on weeds in the interrows, where the cover crops were planted. Orthogonal contrasts showed that tillage, and not the presence of a cover crop, impacted interrow weed biomass. In the interrows, certain weed species were favored (scarlet pimpernel and spiny sowthistle) or discouraged by (California burclover) tillage. This research helps vineyard farmers determine the impact of cover crops and tillage. This accomplishment supports NP303 Plant Disease, Component 4, Problem Statement A.
4. Xylella fastidiosa colonizes plant xylem by both active and passive mechanisms. Xylella fastidiosa (Xf) is a bacterial pathogen that causes numerous devastating plant diseases, including Pierce’s disease of grape, but the exact mechanism of hydraulic disruption and systemic colonization of host xylem remains elusive. The ARS scientists in the Plant Pathology and Genetics Research Unit measured functional and structural characteristics of xylem in organs of both healthy and Xf-infected oak species. Results suggest that the bacteria induce embolism, via pit membrane degradation, in the early stages of colonization, and this is the first step leading to eventual vessel occlusion. Measurements of pit membrane porosity showed that pit membrane pores larger than individual Xf cells occur frequently throughout the secondary xylem and likely facilitate systemic colonization in susceptible oak species. This work provides a better understanding of how this pathogen induces symptoms and moves within its hosts, and may be used to select for structural characteristics that impart resistance. This accomplishment supports NP303, Component 4, Problem Statement B.
5. Significant Activities that Support Special Target Populations