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Naohiro Kubota and Mayumi Miyamuki

Four dormant grapevine (Vitis spp.) cultivars grown under forced conditions were treated immediately after pruning with a paste of fresh garlic, the supernatant of a 20% suspension of CaCN2, and 50% `Merit' solution a foliar fertilizer, to break bud dormancy. Garlic paste significantly accelerated budbreak and increased the rate of budbreak in three cultivars, but for `Delaware,' CaCN2 was more effective. Garlic also affected budbreak of cuttings with a single bud of `Kyoho,' `Neo Muscat,' or `Muscat Bailey A' grapes in a deep stage of dormancy. Garlic paste applied to cool `Muscat of Alexandria' vines immediately after they were pruned in various stages of dormancy (from November to March) accelerated budbreak in the spring when application was made by January. The rate of budbreak was steady, but earlier CaCN2 treatments resulted in a rate of budbreak that was not uniform, although the first budbreak was accelerated. Low concentrations of garlic juice did not promote budbreak of cuttings of `Muscat of Alexandria'. When garlic paste was applied to various parts of cuttings with two buds, budbreak was accelerated when the upper cross-section was treated, but the overall rate of budbreak was highest when the lower half of the cutting was treated. Chemical name used: calcium cyanamide (CaCN2).

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Matthew Fidelibus* and David Smart

In response to diminishing returns, the California raisin industry is rapidly adopting mechanical raisin harvesting practices to reduce cost. Whether the fruit will dry on the vine, or be laid on continuous trays to dry, the first step of mechanical raisin harvest generally involves severing the canes of vines with ripe fruit, a practice known as harvest pruning (HP). The potential physiological implications of HP are uncertain, so an experiment was established to assess the effects of HP on 40-year-old `Thompson Seedless' grapevines (Vitis vinifera L.) that were on their own roots, head-trained and cane pruned, and supported by a single wire trellis. Fruit achieved 20 °Brix by 2 Sept., at which time vines had a leaf area of about 21.6 m2. About 60% of the canopy leaf area was from canes, and thus removed by HP. The net CO2 assimilation rate (A) of mature leaves on renewal shoots began to decline after about 8 Aug., but they maintained a positive A until at least 31 Oct. Reduced A was due, in part, to chlorophyll degradation as evidenced by a decline in SPAD units occurring over the period that A declined. Harvest pruning generally did not affect A of mature leaves retained on renewal shoots, but those leaves maintained a positive A for at least 60 d after HP indicating that HP reduced the vines' photosynthetic capacity. Soil respiration also declined between summer and winter, probably in response to decreasing soil temperatures. Soil respiration was similar among HP and non-HP vines, except about 30 d after HP, when HP vines had about 30% lower soil respiration values than non-HP vines. Root growth was observed in summer and fall regardless of whether vines were subjected to HP.

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Bruce P. Bordelon and Jill Blume

Grapevines (cv. Steuben) were field-grown for 1 year to determine the effects of pruning and grow tube use on vine growth. Plots were grown on Crosby-Miami silt loam soils, trickle irrigated as needed to ensure adequate moisture, and provided a 3-ft band of weed control on each side of the row. Vines were trained onto a 5-ft. tall-trellis using the following techniques: 1) pruned to a single shoot and placed in a grow tube supported by a bamboo stake, 2) pruned to a single shoot and trained on a bamboo stake without a grow tube, or 3) left unpruned and trained on four strings radiating out from the vine to the top wire. At the end of the growing season, the vines were destructively sampled for leaf area, total shoot growth, average internode length, shoot diameter, top growth dry weight, and root system dry weight. The results indicate that pruning vines to a single shoot significantly reduced overall vine growth, whether a tube was used or not. Vines trained to single shoots and grown with or without grow tubes did not differ significantly for the various parameters measured. Unpruned vines produced nearly three times more leaf area, more than two times more total shoot length, and more than two times more top dry weight and root dry weight than the other treatments. A sub-set of these vines will be grown for one more season to determine if the negative effects of pruning and/or tubes will effect vine size after a second season.

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D.C. Ferree and J.G. Streeter

Container-grown `Chambourcin' grapevines were exposed to soil compaction created by changing soil bulk density to determine the effect of levels of compaction, rootstocks and moisture stress on mineral nutrition, leaf gas exchange and foliar carbohydrate levels. Shoot growth, leaf area, number of inflorescences and leaf dry weight decreased linearly as soil bulk density increased with the effects being significant above 1.4 g·cm-3. The early season leaf area was reduced 40% in the second season, but later leaves were unaffected by a soil bulk density of 1.5 g·cm-3. Net photosynthesis (Pn) and transpiration (E) increased linearly with increasing soil bulk density the first year, but the second year a nonlinear pattern was observed with highest rates at 1.3 and 1.4 g·cm-3. Soil bulk density of 1.5 g·cm-3 reduced number of leaves, leaf area and shoot length and advanced bloom 16 days on `Chambourcin' vines on six rootstocks with no interaction of rootstock and soil compaction. Withholding water for 8 days reduced Pn and E in all treatments, with no effect on shoot length, leaf, stem and total dry weights. Moisture stress in the noncompacted soil caused a reduction in leaf concentration of fructose, glucose and myo-inositol, but moisture stress had no effect in the compacted soil. Moisture stress caused a reduction in sucrose in both compacted and noncompacted soil. Compacting soil to a bulk density of 1.5 g·cm-3 was associated with an increase in leaf N, Ca, Mg, Al, Fe, Mn, Na, and Zn and a decrease in P, K, B, and Mo.

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Alireza Talaie*, Vali Rabiei, and Ali Ebadi

Grapevine under arid and semi-arid are subjected to low soil water availability, accompanied by high levels of temperature and severe transpiration in the summer period. In spite of their deep root system, severe water stress may occur during that period. Therefore, study of morphological and physiological responses of grapevine cultivars to water stress, especially during the different phenological stages, are necessary. The effect of water deficit stress on morphological and physiological responses of four Iranian grapevine cultivars (Vitis vinifera L. cvs. Bidaneh Sephid, Yaghooti Shiraz, Khoshnav, and Siaveh) were studied. This investigation was conducted as a factorial experiment in a complete randomized block design with four replications. In this study, 1-year-old own rooted vines were planted outdoor in plastic bags. Water stress was begun 115 days after bud break and contained for 2 months. Some vegetative and biochemical characters of leaves were evaluated; photosynthesis and gas exchange was measured. The results of analysis of variance indicated that water deficit stress decreased total dry weight, root dry weight, leaf area, non soluble carbohydrate concentration, and chlorophyll content. The reduction of leaf area in `Yaghooti Shiraz' and total dry weight and root dry weight in `Bidaneh Sephid' were higher than two other cultivars. Under water deficit stress condition, the soluble carbohydrate concentration and proline content in grapevine cultivars increased. Net photosynthesis and gas exchange rate were markedly reduced in water deficit stressed vines.

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K.A. Roubelakis-Angelakis and S.B. Zivanovitc

A modified culture medium is presented that promotes in vitro rooting of grapevine rootstock and Vitis vinifera L. cultivars even in the absence of plant growth regulators. Study of 15 Vitis genotypes indicated a strong genotype-dependent response to culture medium and growth regulators with respect to formation of roots in onenode shoot segments.

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Jiang Lu, Elvis Clarke, and Zhong-bo Ren

Although some of the American native Vitis species and their hybrids, particularly those originated from the southeastern United States, have been known for resistance to Pierce's disease (PD), their resistant status against the glassy-winged sharp shooter [GWSS, Homalodisca coagulata (Say)], the vector transmitting PD pathogen (Xylellafastidiosa Well), has not been reported. To determine GWSS feeding preferences on different grape species/cultivars and correlations of feeding to Pierce's disease development, a survey was conducted at Florida A&M University, Tallahassee. The feeding preference of GWSS on different species/cultivars was evaluated in two different ways: 1) count the number of GWSS on different grapevines in the field; and 2) determine the feeding preference by measuring the excretion of the GWSS feeding on difference grape species/cultivars, including highly susceptible V. vinifera cultivars, native American grape species and hybrids, and muscadine grapes. Results from this study indicated that the frequency of GWSS visits on different grapevines varied among the species/cultivars investigated. For example, PD-resistant grape V. rotundifolia (muscadine grape) had significantly fewer GWSS visits than did the PD-susceptible V. vinifera grape. The frequency of GWSS visits to V. labrusca, the native American grape susceptible to PD, was intermediate between those found on V. rotundifolia and V. vinifera. Similarly, the GWSS sucked more xylem sap when they fed on PD-susceptible grapevines than on PD-resistant ones. Overall, there is a positive correlation between the GWSS visits/feeding and the status of grapevine resistance/susceptibility to Pierce's disease.

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Pavel Pavloušek

similar to the fruit of sweet cherry. The name ‘Cerason’ originates from the Latin botanical name Cerasus avium . Fig. 1. Mature cluster of ‘Cerason’. Origin At the end of the 19th century, the most important fungal diseases and pests of grapevine in

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N.G. Krohn and D.C. Ferree

Greenhouse and field-grown `Seyval blanc' grapevines (Vitis sp.) were grown with low-growing, shallow-rooted, mat-forming, ornamental perennial groundcovers, and the effect of the groundcovers on the vegetative and fruiting growth of the grapevines was evaluated. The groundcovers used in this experiment were `Kentucky-31' tall fescue (Festuca arundinacea); white mazus (Mazus japoonicus albus); english pennyroyal (Mentha pulegium); dwarf creeping thyme (Thymus serpyllum minus); strawberry clover (Trifolium fragiferum); `Heavenly Blue' veronica (Veronica prostrata `Heavenly Blue'); and a companion grass mixture of 75% perennial ryegrass (Lolium perenne) and 25% red fescue (Festuca rubra). A control treatment grown without any groundcover was also used in both the greenhouse and field experiments. All of the groundcovers reduced `Seyval blanc' total shoot length from 22% to 85% in the vineyard. Cluster size was reduced in the field from 7% to 68% by the groundcovers compared to the herbicide control treatment, and from 9% to 66% in the greenhouse experiment, but none of the groundcovers in either the greenhouse or field experiments affected the pH, total acidity, or soluble solids concentrations of the `Seyval blanc' juice. English pennyroyal was the only groundcover that reduced in the leaf area of the grapevine. Single-leaf photosynthesis of the `Seyval blanc' grapevines in the field experiment was reduced by all groundcovers except mazus and creeping thyme. Water infiltration rates were 10 to 50 times higher in the groundcovers compared to the bare soil of the herbicide control treatment. Weed growth in the field caused reduction in shoot length similar to the most competitive groundcovers. Weed growth was reduced in the early season by the english pennyroyal and companion grass, and in the late season by all groundcovers. The reduction in growth of the grapevines caused by groundcovers in the greenhouse was a reasonable screen for the affect of groundcovers in the field. The mazus treatment was the only groundcover in our experiments that coupled fast growth with low competitive ability.

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William R. Nail and G. Stanley Howell

Potted grapevines (Vitis vinifera L. `Chardonnay') were inoculated with conidial suspensions of the grapevine pathogen causing powdery mildew of grape (GPM) (Uncinula necator (Schw.) Burr.). Leaves of inoculated and noninoculated vines were studied for the effects of varying light (PAR) and CO2 concentrations on factors affecting carbon assimilation. GPM reduced carboxylation efficiency (k), net CO2 assimilation rate (A), stomatal conductance (g s), and internal CO2 concentration (Ci) under ambient CO2, A max at >900 ppm CO2, stomatal limitations to A (lg), and photochemical efficiency (Φ) on diseased leaves, while having no effect on the CO2 compensation point (Γ) or the light compensation point (cp). GPM had no significant effect on chlorophyll fluorescence (Fv/Fm).