Browsing by Author "Wolf, Tony K."
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- Anatomical Developments and the Role of Carbohydrate or Mineral Nutrient Deficiency in Bud Necrosis of 'Riesling' grapevines (Vitis Vinifera L.)Vasudevan, Lakshmi (Virginia Tech, 1997-02-26)Bud necrosis (BN) is observed as an abortion and death of one or more primordia of the developing compound winter bud. Anatomical developments during the onset of BN in 'Riesling' and 'Chardonnay' grapevines were characterized. Examination of ultrathin (1micro m) sections of 'Riesling' buds under a light microscope revealed a zone of compressed cells immediately beneath the primary bud axis within 60 days after budbreak. Cell rupture occurred in that zone within 90 days after budbreak. Scanning electron microscopy revealed a similar pattern of tissue destruction. Based on the hypothesis that BN was caused by essential substrate deficiency, localized carbohydrate deprivaton was attempted by shading of 'Riesling' grapevines and by shoot tip removal. In one experiment, 92% shade was applied for a three-week period at 20, 40, or 60 days after budbreak in one vineyard and at 40 days after budbreak in another vineyard. In another experiment, 92% shade was applied for a 40-day period at 25 or 65 days after budbreak. Shade reduced photosynthetic photon flux (PPF) in the fruit zone of canopies to <2% of ambient PPF. The first experiment did not increase BN. However, the second experiment increased BN in the distal nodes of the shaded vines compared to the control vines. Shoot vigor, measured as shoot diameter and internode length at season1s end, was positively correlated with BN in shaded as well as unshaded vines. The frequency of necrotic buds was greater at nodes 5 through 16 than at nodes 1 to 4 in both shaded and unshaded vines. Levels of total nonstructural carbohydrates (TNC) measured spectrophotometrically, were not significantly affected by shade treatment. Levels of sucrose, glucose, fructose, and starch in bud, leaf, and stem tissues determined by HPLC, were lower in shaded vines at the point of shade removal than in unshaded vines. Therefore, although three-week periods of shade did not affect BN in 'Riesling', 40-day periods of shade increased BN in distal nodes. Shoot tip removal increased BN at nodes distal to node 12. Bud tissues of shoot-tipped vines had lower levels of sucrose, glucose, fructose, and starch than did the control vines. Carbohydrate analysis of bud, leaf, and stem tissues indicated that 'Riesling' vines (BN-prone) had lower levels of sucrose compared to 'Chardonnay' vines (BN-insensitive). Role of mineral nutrient deprivation was examined in 'Riesling' and 'Chardonnay' buds and the results indicated that BN is unlikely caused by essential nutrient deficiency. 'Chardonnay', the BN-insensitive cultivar had greater levels of starch deposits at 50, 60, 70, and 80 days after budbreak than did the BN-susceptible cultivars, 'Riesling1', Syrah', and 'Viognier'. Starch deposits in grape buds were negatively correlated with BN incidence. From these experiments it can be concluded that a negative correlation between carbohydrate levels of grape buds and BN incidence exists.
- Assessment of the Impact of Viticulture Extension Programs in VirginiaFerreira, Gustavo F. C.; Hatch, Tremain; Wolf, Tony K. (2016-10)The study discussed in this article assessed the impact of Virginia Cooperative Extension (VCE) on the Virginia wine grape industry. An online survey was developed and administered to members of the Virginia Vineyards Association. The results indicate that the resources and recommendations VCE and Virginia Tech have provided have been beneficial to Virginia grape growers, although growers who operate larger farms, produce wine commercially, or have higher levels of viticulture training are less likely to benefit from the relevant programs. Growers operating near where the programs are often delivered and those with higher levels of experience have benefited the most.
- Assessment of Vineyard Nitrogen Management upon Grape ChemistryMoss, James Russell (Virginia Tech, 2016-07-29)To combat excessive vine vigor, many vintners have employed intensive cover cropping techniques. While cover crops provide a multitude of benefits to the farming system, they can compete for nutrients and water. The seemingly ubiquitous adoption of cover crops in the Eastern United States has led to vines and grape musts which are deficient in nitrogen (N). A must that is deficient in yeast assimilable nitrogen (YAN) can lead to the production of off aromas and stuck or sluggish fermentations. It has also been suggested that musts with limited amino nitrogen sources can result in wines with less fruity aromas than those with a higher starting amino acid content. Varying rates of calcium nitrate were applied to the soil at bloom and foliar urea was sprayed at a Sauvignon blanc and Petit Manseng (Vitis vinifera L.) vineyard. Perennial White and Crimson clover as well as foliar urea applications at véraison were utilized at a Vidal blanc (Vitis spp.) site. Foliar urea was effective at significantly increasing YANs in all experiments with some year to year variation in efficacy. Foliar urea applications slightly favored the production of ammonia over primary amino nitrogen. While most of the measured amino acids in fruit increased in concentration with the application of either soil or foliar N, foliar applications were more effective at increasing fruit amino acids. Of the amino acids measured, arginine and glutamine were the most increased by foliar urea applications, whereas proline was relatively unaffected. The use of clover as a perennial under-vine cover crop did not increase berry YAN. The application of foliar urea sprays may present an effective means by which vintners can easily increase must YANs and amino acid contents.
- A Business Plan for a Norton Vineyard to be Established in VirginiaSheldon, David R. (Virginia Tech, 2016-06-27)This report specifically addresses the work and moneys required to set up from ground zero a vineyard totally devoted to raising Norton grapes to meet market need. It provides the thought process to determining a financially feasible vineyard, exhibits a year-to-year cash flow and income analysis as the vineyard reaches maximum revenue potential, and offers the information in a Business Plan format so that outside viewers can make their own objective conclusion regarding the profit potential of such a venture.
- Determining the threat of Pierce's disease to Virginia vineyardsWallingford, Anna Kate (Virginia Tech, 2008-07-10)Pierce's disease (PD) is a vascular disease of grapevines caused by Xylella fastidiosa (Wells et al.) (Xf) which is transmitted by xylophagous insect vectors. PD infection in Virginia vineyards was thought to be isolated to southeastern portions of the state as there have been no reports of vine loss in western Virginia and cold winter temperatures experienced there limit the effects of the bacterium from year to year. Upward trends in winter temperatures have raised PD concern in the mid-Atlantic. My risk assessment study found PD symptomatic vines beyond the modeled boundary for infection, confirmed Xf-positive with DAS-ELISA. Yellow sticky traps were used to survey Virginia vineyards throughout the 2006 and 2007 growing seasons to identify sharpshooter (Cicadellinae) species in six growing regions. Graphocephala versuta (Say) and Oncometopia orbona (Fabricius) (Hemiptera: Cicadellidae) were trapped in the greatest abundance and were both present in every region surveyed. This study uses geographical representation of climatological data to estimate risk for Pierce's disease.
- Effects of Horticultural Oils on Photosynthesis, Fruit Maturity, and Yield of Wine GrapesFinger, Sarah Adine (Virginia Tech, 2000-05-02)In field experiments conducted in northern Virginia during 1998, oils reduced photosynthesis, fruit maturity, and crop yield. Three applications of a 1.5% (v/v) oil/water emulsion were made to Chardonnay and Cabernet Sauvignon vine canopies at 6200 L/ha (Chardonnay) and 2440 L/ha (Cabernet Sauvignon). Net assimilation rate (NAR), soluble solids concentration (SSC), and berry size were reduced by oil treatments when compared to an untreated control. Also in 1998, a 1.5% (v/v) oil/water emulsion at 5550 L/ha and 4680 L/ha was applied to 23 wine grape cultivars. Eleven cultivars had significant foliar injury but injury was not related to reductions in fruit maturity. Experiments conducted in 1999 determined if reduced spray volumes or applications to only the fruit zone minimize reductions in NAR and SSC. Chardonnay and Cabernet Sauvignon were treated with JMS Stylet oil (1.5%) using 5600 L/ha or 1870 L/ha applied to the whole canopy or 930 L/ha applied to the fruit zone. The NAR of 5600 L/ha treated Cabernet Sauvignon was significantly lower than the NAR of control and other oil treatments on three measurement dates. The NAR of Chardonnay in the 5600 L/ha treatment was significantly lower than the NAR of control treatments in three measurements. Cabernet Sauvignon SSC was reduced by the 5600 L/ha and 1870 L/ha treatments, relative to the water treated control, on three sample dates but not at harvest. The SSC of Chardonnay in the 5600 L/ha treatment was reduced at harvest as compared to all other treatments. The SSC of Chardonnay in the 1870 and 930 L/ha treatments was reduced relative to the water control. Low volumes of oil caused less reduction in NAR and SSC; however, there are concerns about the efficacy of oils used at low volumes due to poor coverage.
- Effects of horticultural oils on the photosynthesis, fruit maturity, and crop yield of winegrapesFinger, Sarah A.; Wolf, Tony K.; Baudoin, Antonius B. (American Society for Enology and Viticulture, 2002)The effects of horticultural oils on grapevine photosynthesis, fruit maturity, and crop yield components in field experiments were evaluated. Three applications of a 1.5% (v/v) oil/water emulsion were made to Chardonnay and Cabernet Sauvignon vine canopies at 6200 L/Ha (Chardonnay) and 2440 L/Ha (Cabernet Sauvignon) in 1998 using several horticultural oils. Net assimilation rates (NAR) and fruit soluble solids concentrations (SSC) were reduced in both cultivars by all oils, as compared to the control. In addition, berry weights, cluster weights, crop per vine, and vine pruning weights were all reduced by oil treatments to Chardonnay vines. Experiments in 1999 sought to determine if reduced spray volumes or applications to only the fruit zone minimized reductions in NAR and SSC. Chardonnay and Cabernet Sauvignon were treated twice with JMS Stylet-Oil(TM) (1.5%) using 5600 L/Ha or 1870 L/Ha applied to the whole canopy or 930 L/Ha applied only to the fruit zone. The NAR of 5600 L/Ha-treated Cabernet Sauvignon was significantly lower than the NAIR of 1870 L/Ha oil-treated vines on three of four subsequent measurement dates. The NAR of Chardonnay in either the 1870 or 5600 L/Ha whole canopy oil treatments was significantly lower than the NAR of the water treatment at all measurement dates. Oil application to only the fruit zone (930 L/Ha) reduced the negative impact on NAR. Cabernet Sauvignon fruit SSC was consistently reduced by the 5600 L/Ha and 1870 L/Ha treatments, relative to the water-treated control. Similarly, the SSC of Chardonnay fruit in the 1870 and 5600 L/Ha treatments was consistently reduced compared to controls. Oil effects on fruit pH and titratable acidity were occasionally observed. While horticultural oils may serve as effective fungicides, our results highlight the potential negative impacts they can have on fruit composition and fruitfulness if used excessively.
- Effects of prohexadione-calcium on grape yield components and fruit and wine compositionLo Giudice, Danielle; Wolf, Tony K.; Zoecklein, Bruce W. (American Society for Enology and Viticulture, 2004)Prohexadione-calcium (prohexadione-Ca) was applied to field-grown Cabernet franc, Cabernet Sauvignon, Chardonnay, and Seyval to evaluate rates and timing effects on fruit yield components and on fruit and wine composition. Berries per cluster, berry weight, cluster weight, and clusters per shoot in the subsequent season were all decreased by multiple, prebloom plus postbloom, applications to Cabernet Sauvignon and Cabernet franc. Similar reductions in current season components of yield were observed with Seyval. Application (250 mg/L) to single clusters of Cabernet Sauvignon and Chardonnay at bloom, or in the one-to-two-week prebloom period decreased fruit set, whereas applications one to two weeks postbloom reduced berry weight, with no impact on fruit set. Berry weight reduction correlated to increased color intensity (420 nm + 520 nm), total anthocyanins, total phenols, and phenol-free glycosyl-glucose (PFGG) in Cabernet Sauvignon. In a separate experiment, prohexadione-Ca increased Cabernet franc must color intensity, total anthocyanins, and total phenols, despite having, minimal effects on berry weight or crop yield. Aroma and flavor triangle difference tests did not distinguish treatment differences with young Cabernet franc wines. This study of prohexadione-Ca effects on grape reproductive development illustrated that berry set and berry weight were responsive to application timing, with the one-to-two-week period after bloom most sensitive to reductions in berry weight. The concurrent effects on fruit composition were generally positive, while the full impact on wine quality remains equivocal, but worthy of further evaluation.
- Evaluation of Nitrogen Management Schemes upon Vine Performance in Cover Cropped VineyardsMoss, James Russell (Virginia Tech, 2016-07-29)Vineyards in the Eastern United States are often prone to excessive vegetative growth. In order to suppress excessive vine vigor, many viticulturists have employed cover cropping strategies. Cover crops provide a myriad of agronomic benefits, however they are known to compete with the vine for water and nutrients. Due to the widespread use of cover crops in Eastern vineyards, many vineyards experience nitrogen (N) deficiencies in both the vegetative vine tissue and yeast assimilable nitrogen (YAN) in the juice. Soil applications of calcium nitrate and foliar applications of urea were assessed as a means of vineyard N amelioration at cover cropped sites comprised of Petit Manseng and Sauvignon blanc (Vitis vinifera L.). Perennial White and Crimson clover cover crops and foliar urea applications were also used in a Vidal blanc (Vitis spp.) vineyard. Treatments were imposed in the Sauvignon blanc vineyard for five years. The Petit Manseng and Vidal blanc vineyards were subjected to treatments for two years. Soil-applied N at bloom was most effective at increasing leaf petiole N at véraison, season-long chlorophyll content index (CCI), vine capacity and fruit yield. Fruit yield was increased due to more berries per cluster and greater berry weights. Increased rates of soil-applied N decreased the fruit weight:pruning weight ratio. Clover cover crops offered little to no benefit as a N source in the two-year period of evaluation. None of the N management schemes negatively impacted canopy density, fruit zone light interception, or botrytis bunch rot incidence. The combination of both a soil-applied and foliar-applied N fertilizer may be the most effective means to increase both vine capacity and YAN in vineyards where vineyard floor cover crops are compromising vine N status.
- Expansion of the range of Pierce’s disease in VirginiaWallingford, Anna K.; Tolin, Sue A.; Myers, Ashley L.; Wolf, Tony K.; Pfeiffer, Douglas G. (2007)Pierce’s disease (PD) is a vascular disease of grapes caused by the bacterium Xylella fastidiosa Wells et al. and vectored by xylem-feeding sharpshooters (1). Symptoms of PD occur when bacteria proliferate the xylem; both the bacteria (2) and host responses to infection (3) block the flow of xylem fluid to the shoots. Affected grapevines show interveinal chlorosis, marginal necrosis with marginal yellow or red line (Figs. 1 and 2), green islands on shoot bark after normal tissue turns brown, and leaf abscission from the distal end of petioles, leaving characteristic "matchstick petioles" with necrotic tips (Fig. 3). Infection leads to vine decline, yield loss, and, within two to three years, vine death. Although the northern distribution of X. fastidiosa [* see Erratum] extends at least into New Jersey, observations of PD have been limited to vineyards on the Delmarva Peninsula and extreme southeastern Virginia; interior Virginia was considered at low risk of PD because of its low winter temperatures (lethal to the bacteria), based on the results of past research that showed lower pathogen populations in plants grown at low temperatures in a growth chamber (4). Recent warm winters have, however, increased our concerns about vulnerability of other Virginia vineyards to PD. Our objective was to conduct a state-wide survey of Virginia’s vineyards for presence of X. fastidiosa.
- Fungicide Sensitivity of Erysiphe necator and Plasmopara viticola from Virginia and nearby statesColcol, Jeneylyne Ferrera (Virginia Tech, 2008-08-01)This study was undertaken to determine the sensitivity of grape downy mildew (DM, Plasmopara viticola) and powdery mildew (PM, Erysiphe necator) to commonly used single-site fungicides in Virginia and nearby states. DM and PM isolates were collected from 2005 to 2007. In grape leaf disc bioassays, 92% of the DM isolates were QoI (azoxystrobin)-resistant, but none were resistant to mefenoxam. Eighty-two percent of the PM isolates were QoI-resistant, but none were resistant to boscalid and quinoxyfen. The frequency of the G143A point mutation, which confers high levels of QoI resistance, was quantified in DM and PM isolates by real-time PCR. Most of the QoI-resistant DM and PM isolates contained >95% of the 143A allele. QoI-sensitive DM isolates contained less than 1% of 143A. One out of 145 and 14 out of 154 QoI-resistant DM and PM isolates (able to grow on azoxystrobin concentration ï ³ 1 µg/ml), respectively, contained less than 1% 143A. Most PM isolates exhibited reduced sensitivity to five DMI fungicides when compared to a sensitive subgroup (n=9) and compared to published reports for unexposed populations; the resistance factor (median EC50 of the entire isolate collection divided by median EC50 of sensitive subgroup) was highest for tebuconazole (360) and myclobutanil (350), followed by triflumizole (79), triadimefon (61), and fenarimol (53). Sensitivities to all five DMI fungicides, but also azoxystrobin, were moderately to strongly correlated (pairwise r-values ranging from 0.60 to 0.88).
- Genotyping Points to Divergent Evolution of 'Candidatus Phytoplasma asteris' Strains Causing North American Grapevine Yellows and Strains Causing Aster YellowsDavis, Robert E.; Dally, Ellen L.; Zhao, Yan; Wolf, Tony K. (2018-09)Grapevine yellows diseases occur in cultivated grapevine (Viris vinifera L.) on several continents, where the diseases are known by different names depending upon the identities of the causal phytoplasmas. In this study, phytoplasma strains associated with grapevine yellows disease (North American grapevine yellows INAGY]) in vineyards of Pennsylvania were characterized as belonging to 16S ribosomal RNA (rRNA) gene restriction fragment length polymorphism group 16Srl (aster yellows phytoplasma group), subgroup 16Srl-B (1-B), and variant subgroup I-B*. The strains (NAGY1 strains) were subjected to genotyping based on analyses of 16S rRNA and secY genes, and to in silico three-dimensional modeling of the SecY protein. Although the NAGY1 strains are closely related to aster yellows (AY) phytoplasma strains and are classified like AY strains in subgroup I-B or in variant subgroup I-B*, the results from genotyping and protein modeling may signal ongoing evolutionary divergence of NAGY1 strains from related strains in subgroup 16Srl-B.
- Geographic Analysis of Viticulture Potential in VirginiaBoyer, John D. (Virginia Tech, 1998-09-15)The state of Virginia was analyzed to establish its suitability for grape culture. This investigation occurred in two phases: a small scale analysis that encompassed the entire state, and a large scale analysis which focused on site selection at the local level. After identifying regions across the state in terms of their viticulture potential, a study area was chosen from within the highest ranking region. This study area was the focus for the local-scale site potential analysis. First, to delineate regions across Virginia that had greater or lesser viticulture potential from a physical and climatological basis, weather station data were collected for minimum winter temperatures, maximum summer temperatures, precipitation, length of growing season, and day versus night temperature differentials. In addition, elevation and slope models were constructed to complement the climatic variables in identifying areas that contained factors most conducive to grape production. To validate this regional assessment, the history of fruit industries within the state are outlined geographically to display the evolution of the fruit industries, and to establish the factors which have shaped the current fruit landscape. Secondly, at the local scale, a Geographic Information System (GIS) approach was used to identify sites at the county scale that had greater or lesser viticulture potential from a physical basis. Composite maps, constructed by individual counties in the state, were produced from a series of physical databases. The individual databases (sources and resolution in parentheses) included land-use (Virginia Gap Analysis; 30meter2 resolution), slope, aspect, and elevation (USGS 1:24,000 Digital Elevation Model; 30meter2), and soils data (USGS Digital Line Graph (DLG-3)). Each physical feature layer was given a numerical classification, then all layers were combined to produce a 0 to 100 scale in the final, composite image. Given this model of potential vineyard suitability, existing fruit operations in select counties were geo-located on each feature layer using a Global Positioning System (GPS: 1-2meter accuracy). Actual data on occurrences of frosts, minimum winter temperatures, and other site variables were collected from these fruit operations and surrounding weather stations as a sample to validate the model. A strong correlation between areas containing characteristics of current fruit acreage--namely apple--and sites high in potential for viticulture according to the model. Studying the history of geographic distribution of apple and grape industries across the state reinforces the regional assessment of viticulture potential, formulated by the climatic and topographic analysis. Employment of GIS approach at the local site scale was shown to be an effective tool for site selection at the local scale with certain caveats. In addition, the evaluation procedure integrating GIS and GPS technologies allows us to visually assess the distribution pattern of each of the factors employed individually; and, in turn, physically identify and locate areas of viticulture potential created from the combination of those factors.
- Grape Production Injuries and PreventionGrisso, Robert D.; Wolf, Tony K.; Niewolny, Kimberly L. (Virginia Cooperative Extension, 2020-10-23)Grape acreage and production have been steadily increasing in the US. In 2010 there were approximately 23,000 farms with a total of 944,800 acres producing grapes. Ninety percent of these farms are smaller than 100 acres and about 16,000 of these were vineyards. California accounts for about 90% of the total production in the US. The next two largest grape producing states are Washington and New York and they produce approximately 6% and 2% respectively (NASS-USDA, 2014)
- Groundcover, rootstock and root restriction effects on vegetative growth, crop yield components, and fruit composition of Cabernet SauvignonHatch, Tremain Archer (Virginia Tech, 2010-02-04)Wine vineyards in humid environments like the mid-Atlantic United States are characterized by vines that develop too much vegetative growth for optimum quality wine production. Cover crops, rootstocks and rootzone restriction were evaluated for their effect on vegetative and reproductive growth on Cabernet Sauvignon. Treatments were arranged in a strip-split-split plot arrangement with under-trellis cover crops (UTCC) compared to row-middle only cover crop combined with 1-m weed-free strips in the vine row as main plots. Rootstocks riparia Gloire, 420-A, and 101-14 were sub-plots, while sub-sub-plots comprised two treatments: vines were either planted in root-restrictive (RR), fabric bags (0.016 m3) at vineyard establishment (2006), or were planted without root restriction. All three factors were effective in suppressing vegetative development as measured by rate and extent of shoot growth, lateral shoot development, trunk circumference, and dormant pruning weights. Canopies of vines with UTCC and RR had reduced leaf layer values by approximately 21% and 23% compared to conventional controls. The principal effect of the UTCC and the RR treatments was a sustained reduction in stem (xylem) water potential. UTCC and RR caused significant 7 and 10% reductions in berry weight, compared to their conventional controls. Berry weights of vines grafted to riparia were greater than those of vines grafted to other rootstocks. Wine made from UTCC and RR treatments increased red wine color compared to herbicide UTGC and NRR, respectively. This study identified treatments that improve vine balance while simultaneously improving grape composition and potential wine quality.
- Neoseiulus fallacis (Garman) (Acari: Phytoseiidae) as a potential biological control agent for spider mites (Acari: Tetranychidae) in Virginia vineyardsMetzger, Jessica A. (Virginia Tech, 2001-01-18)Outbreaks of spider mites (Acari: Tetranychidae) in vineyards have been increasing with the expansion of the industry in Virginia. Only three effective acaricides are registered on grapes and as resistance begins to occur, control options are limited. Biological control of spider mites by inoculative or inundative releases of predatory mites has been tried on a wide range of crops including grapes. This project examined the feasibility of using Neoseiulus fallacis (Acari: Phytoseiidae) as a potential large-scale biological control agent in vineyards. Slide dip bioassays were conducted on N. fallacis to determine the toxicity of insecticides, fungicides and herbicides commonly used on grapes in Virginia. In addition to laboratory experiments, commercially obtained N. fallacis were released in vineyards with spider mite infestations. The populations of both mites were then monitored on a regular basis to determine dispersal and distribution patterns. Among the insecticides tested in the laboratory bioassays, carbaryl, azinphos-methyl, phosmet, cyhexatin, and pyridaben all caused significantly higher mortality than the control treatment. Fungicides tested were not toxic to the predator, but three herbicides caused high mortality. Glufosinate caused 100% mortality after 24 hours and both oxyfluorfen and paraquat had adverse effects on N. fallacis. The use of materials that were found to be toxic to the predator would not be compatible with inoculative releases of N. fallacis. Field release results were variable. Three releases were made in 1999 and 2000., Recovery of the predator was low following the releases at two of the sites, probably due to lack of prey. At the third site enough predators were recovered to analyze the spatial distribution of the predator and prey populations. It appears that there is no similar aggregation pattern between the predator and prey at the same point in time although there is an indication of the predator spreading is response to the prey distribution. A more complete season of sampling would give more conclusive evidence of this trend. Although the distribution of the two populations were dissimilar, the predator was present throughout the season and did spread through the entire plot indicating that the predator may be able to colonize the vineyard if it successfully overwinters.
- The Impact of Prohexadione-calcium on Grape Vegetative and Reproductive Development and Wine ChemistryLo Giudice, Danielle (Virginia Tech, 2002-05-14)Prohexadione-calcium (P-ca), as ApogeeTM, was evaluated in 2000 and 2001 for impact to grape vegetative and reproductive development. In 2000, P-ca (250 mg/L) was applied to Seyval, Cabernet Sauvignon, and Cabernet franc (125, 250, and 375 mg/L). P-ca reduced primary shoot growth for all cultivars and decreased cane pruning weight of Seyval. P-ca (375 mg/L) increased Cabernet franc canopy gaps but increased Cabernet Sauvignon lateral leaf area and leaf layer number. P-ca reduced components of yield for all cultivars. In 2001, P-ca (250 mg/L) was applied singularly at weekly intervals to Cabernet Sauvignon clusters and pre and post-bloom to Cabernet franc and Chardonnay canopies. Application at E-L stages 21 and 23 decreased Cabernet Sauvignon fruit set whereas application at E-L stages 26, 27, and 29 reduced berry weight without impacting fruit set. Berry weight reduction correlated to higher color intensity (420+520 nm), anthocyanins, total phenols and phenol-free glycosyl-glucose (PFGG). Cabernet franc vegetative and reproductive development was generally not affected yet treatment increased absorbance at 280, 420, and 520 nm, color intensity, anthocyanins and total phenols. Pre-bloom applications inhibited Chardonnay vegetative development, and reduced components of yield, and fruit chemistry values: hydroxycinnamates, total phenols, flavonoids, PPFG and absorbance at 280 and 320 nm. Post-bloom applications did not affect Chardonnay vegetative or reproductive development, yet increased PFGG. Treatment did not affect Chardonnay wine chemistry but two post-bloom applications increased Cabernet franc wine anthocyanins and total phenols. Wine aroma and flavor triangle difference tests did not indicate significant treatment differences.
- Investigation of Regulatory Mechanisms of Chemical-Mediated Fruit Thinning in Apple (Malus X Domestica Borkh.)Zhu, Hong (Virginia Tech, 2010-12-06)Fruit thinning is critical to the success of apple industry because most apple trees are prone to biennial bearing characterized by heavy bloom and over-cropping in the "on" year and low or no cropping in the "off" year. Fruit thinning can improve fruit size, increase return bloom, and reduce alternate bearing habit of apple trees. Chemical thinning has been widely used as a horticultural practice by growers for years in apple and other fruit production. However, its thinning results are often variable and very difficult to predict since parameters as well as their interactions (e.g. concentration, environmental condition, cultivar response) that affect thinning effectiveness have been poorly defined and the regulatory mechanisms at molecular level remain to be illustrated. Therefore, the purpose of this study is to characterize the physiological and molecular responses of the apple trees to the thinning treatments, and then use key genes as molecular markers for screening potential thinning agents. The long-term goal is to understand how the applied chemicals and environmental factors interact and regulate key regulatory genes as well as the thinning effectiveness during thinning process, and establish a predictable model for the improvement of fruit thinning consistency and effectiveness in apple and other fruit trees. Effects of naphthaleneacetic acid (NAA), shading, amimoethoxyvinylglycine (AVG) and 1-methylcyclopropene (1-MCP) on young apple fruit abscission, leaf and fruit ethylene production, and the expression of genes related to ethylene biosynthesis, perception and cell wall degradation were examined in "Golden Delicious" apples (Malus x domestica borkh.). NAA at 15 mg·L-1 and shading increased fruit abscission and ethylene production of leaves and fruit when applied at a 12-mm stage of fruit development, whereas AVG, an inhibitor of ethylene biosynthesis, at 250 mg·L-1 reduced NAA-induced fruit abscission and ethylene production of leaves and fruit. 1-MCP at 160 mg·L-1 had no effect on fruit abscission but induced ethylene production by both leaves and fruit. Changes in the gene expression pattern responding to each treatment were analyzed by real-time quantitative PCR. NAA treatment was found to enhance the expression of genes related to ethylene biosynthesis (MdACS5A, MdACS5B and MdACO1) and perception (MdETR1, MdETR1b, MdETR2, MdERS1 and MdERS2). AVG reduced NAA-induced expression of these genes except for MdERS2 in the fruit abscission zone (FAZ). NAA increased the expression of a polygalacturonase gene (MdPG2) in the FAZ but not in the fruit cortex (FC), whereas AVG reduced NAA-enhanced expression of MdPG2 in the FAZ. These results suggest that ethylene biosynthesis, ethylene perception, and MdPG2 gene are involved in young fruit abscission caused by NAA. On the other hand, 1-MCP did not affect the expression of MdACS5A and MdACS5B in the FAZ, although it enhanced the expression of these two genes in the FC from 6 to 24 hours post-treatment. The expression of MdACO1 in both tissues was increased by 1-MCP after 3 or more days post-treatment. 1-MCP had only a small influence on the expression of most ethylene receptor genes, with the exception of MdETR1, which was up-regulated in the FC to a level similar to that observed for NAA treatment. In response to 1-MCP, in the FAZ, the expression of MdCel1 and MdPG2 was up-regulated at the beginning and the end, respectively, of the experiment, but otherwise remained at or below control levels. 1-MCP did not inhibit NAA-induced abscission of young apple fruit, suggesting that abscission does not solely depend on ethylene signal transduction, or that the periods of effectiveness for 1-MCP and ethylene were asynchronous in this study. Gene expression analysis also revealed that both NAA and shading enhanced the expression of gene related to ABA biosynthesis in the FAZ, which suggested the involvement of ABA in young fruit abscission. Global gene expression profile during young fruit abscission was analyzed using an apple oligonucleotide microarray. More than 700 genes were identified with reproducible changes in transcript abundance in the FAZ after NAA treatment. Genes associated with abscission, ethylene, ABA, cell wall degradation, mitochondrial activity, glycolysis, lipid catabolism, secondary metabolism, abiotic stress, and apoptosis were upregulated, while genes involved in regulation of cell cycle, cell wall biosynthesis, photosynthesis, carbon fixation, chromatin assembly, auxin transport/efflux, cytoskeleton function, and flower development were generally downregulated. Comparison of changes in the gene expression patterns during NAA-induced fruit abscission with shading-induced fruit abscission revealed similarities, but also considerable differences. The data suggested that young fruit were shutting down growth and energy production and undergoing a certain kind of programmed cell death (PCD) induced by these different stimuli. Gene expression analysis in abscising young fruit revealed that photosynthesis, carbon utilization, and ABA/ethylene pathways appeared to operate in both NAA- and shading-induced fruit abscission. However, more sugar signaling genes were regulated in shading-induced fruit abscission, compared to NAA-induced fruit abscission.
- Jikradia olitoria ([Hemiptera]:[Cicadellidae]) transmits the sequevar NAGYIIIβ phytoplasma strain associated with North American grapevine yellows in artificial feeding assaysLenzi, Paolo; Stoepler, Teresa M.; McHenry, Diana J.; Davis, Robert E.; Wolf, Tony K. (Library of the University of Arizona, 2019-01-02)North American Grapevine Yellows (NAGY) is a destructive disease of grapevines caused by phytoplasmas, wall-less bacteria that are insect-transmitted and found in plant phloem tissues. Although the disease was recognized in vineyards in the eastern United States since the 1980s, the identities of vectors remain unknown. The objectives of this study were to survey potential phytoplasma vector insects inhabiting Virginia vineyards that expressed NAGY symptoms and to evaluate their ability to transmit phytoplasmas associated with NAGY. Phytoplasmas were identified as 'Candidatus Phytoplasma pruni'-related NAGYIIIβ strains and 'Ca. Phytoplasma asteris'-related NAGYI-B strains. To determine the identities of the potential vectors, artificial feeding solution was used to evaluate the ability of leafhopper species to release phytoplasmas during feeding and phytoplasma strains were identified using molecular tools. Out of 49 insect species screened, Jikradia olitoria was the only insect that released phytoplasmas into the feeding solutions; all phytoplasmas, thus, detected were identified as NAGYIIIβ strains by nucleotide sequencing of three different genomic regions. No NAGYI-B strain was detected. To our knowledge, this is the first evidence of a potential insect vector of a specific phytoplasma associated with NAGY disease, and it is the first report of J. olitoria being a putative vector of a plant pathogenic phytoplasma. © Published by Oxford University Press on behalf of Entomological Society of America 2019. This work is written by (a) US Government employee(s) and is in the public domain in the US.
- The Relationship Between Mineral Nutrition and Late-Season Bunch Stem Necrosis of Cabernet Sauvignon (Vitis vinifera L.) GrapevinesCapps, Eric R. (Virginia Tech, 1999-04-13)Late-season Bunch Stem Necrosis (BSN) is observed as a necrosis of the cluster stem (rachis) that leads to shriveling of berries on the affected portion of the cluster. Field experiments were conducted over three years at two vineyards in northern Virginia to examine relationships between specific nutrients and the incidence of BSN of Cabernet Sauvignon grapevines. Nutrients, used alone or in combination, included nitrogen, magnesium, and calcium. During the 1997 and 1998 seasons at Leesburg vineyard, applications of nitrogen, magnesium, and calcium produced little change in bloom-time petiole mineral concentration. Fertilizer treatments appeared to have no effect on BSN incidence, but the incidence of BSN was less than or equal 1% in the control plots each year. During the 1996 season at Winchester vineyard, bloom-time leaf petiole and véraison rachis nitrogen concentration of unfertilized (control) vines were 0.80% and 1.16%, respectively. The corresponding control BSN incidence was 41% at harvest time. Application of nitrogen fertilizer at 112 kg/ha actual nitrogen increased bloom-time leaf petiole and véraison cluster stem nitrogen concentration to 1.85% and 2.18%, respectively. The corresponding BSN incidence was reduced to 14% at harvest time. BSN symptoms were not as pronounced during the 1997 season; however, all treatments, including the control plots, had elevated nitrogen levels in 1997. During the 1998 season, bloom-time leaf petiole and véraison rachis nitrogen concentration of unfertilized vines were 0.88% and 0.98%, respectively. The corresponding BSN incidence was 23% at harvest time. Application of nitrogen fertilizer again increased bloom-time leaf petiole and véraison rachis nitrogen concentration to 1.18% and 1.34%, respectively. Corresponding BSN was reduced to 3% at harvest time. Magnesium and calcium had no impact on BSN incidence; however, BSN symptoms were reduced when either was combined with nitrogen fertilizer. The relationship between mineral nutrition and BSN incidence at Leesburg was inconclusive. The BSN of Cabernet Sauvignon at Winchester was, however, positively associated with depressed bloom-time petiole total nitrogen concentrations. Véraison rachis analysis consistently revealed an increase in nitrogen concentration due to application of nitrogen fertilizer. Véraison tissue analysis may be a good diagnostic tool of vine nitrogen status. Magnesium and calcium appeared not to be involved in the disorder. The results illustrate that BSN-prone vineyards should be individually examined for nutrient imbalance or other stresses that may be contributing to BSN.