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Edward W. Hellman and Laurel Raines

The cuticle and epicuticular wax layer of grape berries provides a first line of defense against fungal pathogens. A relatively thick cuticle and wax layer may result in enhanced resistance to Botrytis cinerea Pers. The structure of epicuticular wax also has been postulated to play a role in Botryris resistance.

To examine the role of cuticle and wax in disease resistance, berries of diverse grape cultivars were sampled to quantify the cuticle and wax layers. Wax surface structure was examined by scanning electron microscopy. Significant differences among cultivars were found for both cuticle and wax measurements. Environmental conditions may influence development of these layers, some cultivars had significantly greater cuticle and wax layers in berries that developed in full sunlight. Visual differences in surface wax appearance were apparent among cultivars. Size, density and orientation of wax platelets varied among cultivars.

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Steven C Wiest and Edward W. Hellman

Scanning electron micrographs of grape berry surfaces, which resemble mountainscapes, contain a wealth of structural information. A typical statistical characterization of features such as root mean square peak-to-peak spacings, peak density, etc., is readily performed on these images. However, a much richer base of information is accessible by analyzing the images with fractal geometry. Fractal box dimension is a quantitative measure of surface roughness, and varies with the contour at which it is determined in both cultivars `Foch' and `Perlette', suggesting that the surfaces are multifractal structures. Fourier spectral analyses of the surfaces produce a similar conclusion. Thus, the unambiguous quantitative resolution of cultivars on the basis of their wax surface structure looks promising, but requires further work.

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Cassandra M. Plank, Edward W. Hellman and Thayne Montague

Methoxypyrazines (MPs) are fruit-derived extractable compounds that contribute to cultivar-specific aroma traits in wine, and greater concentrations can contribute to unpleasant vegetative aromas. Both light exposure and temperature have been reported to influence MP content in developing wine grapes, but individual effects of light and temperature are confounded. A novel method of manipulating light exposure with light-emitting diodes (LEDs) was used to impose light treatments with little or no effect on cluster temperature. Three treatments were imposed on developing fruit of Vitis vinifera (cv. Cabernet Sauvignon): 1) clusters exposed to direct sunlight, 2) clusters shaded by the grapevine canopy, and 3) clusters shaded by the canopy and exposed to supplemental LED light. Experiments were conducted over 3 years across pre- and postveraison periods of fruit development. A second experiment imposed the same light exposure treatments to ripening clusters on vines experiencing continual shoot growth during the postveraison period. Light exposure reduced 3-isobutyl-2-methoxypyrazine (IBMP) concentration of developing grape berries in the preveraison period independently of berry heating from solar radiation. Berry IBMP responded less to postveraison light levels, except on vines with active shoot growth, suggesting IBMP synthesis was continued during active vine growth but was suppressed by light. An inverse relationship of growing degree days (GDDs) with berry IBMP was observed, indicating high temperatures also reduce berry IBMP concentration. Response to temperature could result from either radiant heating of light-exposed clusters or from high ambient air temperature. Canopy management should consider the impact of both light and temperature on IBMP, and vine management practices should be adjusted appropriately to regional growing conditions and grape cultivars.

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Eric T. Stafne, Edward W. Hellman, R. Keith Striegler, James A. Wolpert and Jean-Mari Peltier

Industry involvement is a critical aspect of the Specialty Crops Research Initiative (SCRI). Both a mandate for need and funding are necessary from industry to develop a successful SCRI project. The National Grape and Wine Initiative (NGWI), a nationwide coalition representing all segments of the grape (Vitis sp.) industry including raisin, juice, fresh grape and wine interests, identified extension education as a critical need and charged its extension/outreach committee to concentrate on ensuring industry members are aware of and have access to findings from grape and grape products research. To achieve this goal, the committee decided that a comprehensive online information and educational resource would play an important role. In 2009, the eXtension Grape Community of Practice (GCoP) was funded by the SCRI. The NGWI was active in soliciting letters of endorsement and buy-in from the industry for the project. The Missouri Wine and Grape Board (MWGB) also contributed $20,000 per year for three years to help offset the matching requirement. Research-based grape proposals in subsequent rounds of the SCRI in 2010 and 2011 wishing to have the approval of NGWI have been strongly encouraged to include the GCoP as a portion of their extension component. For the 2011 round of SCRI proposals, this led to the GCoP being included in three projects, two of which were funded. Exploration of future avenues for funding will include subcontracts from other grant awards, NGWI, industry sponsorships, and other creative methods.

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Elvis A. Takow, Edward W. Hellman, Andrew G. Birt, Maria D. Tchakerian and Robert N. Coulson

A geographic information system (GIS) application was developed containing 18 layers of spatially explicit environmental data relevant to characterization of the eight officially recognized American Viticultural Areas (AVAs) for wine grape (Vitis vinifera) production in Texas. GIS climate variables included daily minimum temperature, daily maximum temperature, daily average temperature (TAVG), growing degree days (GDD), ripening period mean temperature (RPMT), annual precipitation, solar radiation, vapor pressure, and number of frost days. Soil attributes were texture, depth, available water capacity, pH, permeability, and bulk density. These data were used to develop interpretative descriptions of Texas AVAs published on the Winegrowing Regions of Texas web site, which also serves as the public portal to the interactive GIS (AVATXIS). Individuals can use AVATXIS to access data and visualize spatial variability on maps to characterize Texas AVAs for any or all of the environmental factors and to examine spatial relationships among factors.