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N. Shlamovitz, P. Spiegel-Roy, and E. Tanne

In many cases the diagnosis of a viral disease in perennial woody plants requires indexing by grafting on indicator plants. In the case of grapevine leafroll and corky-bark diseases, indexing requires 2 to 3 years for symptom recording. Both diseases are found in all grapevine-growing countries. It would therefore be advantageous to develop a sensitive, quick, and reliable diagnostic technique. Explant shoots infected with corky-bark were micrografted onto healthy indicator rootstocks and maintained in vitro. Typical corky-bark symptoms appeared on the indicator within 8 to 12 weeks. Osmotic stress, in vitro, induced by sorbitol, enhanced leafroll symptoms. Explants expressed symptoms after 2 to 3 months of growth on these media. The advantages of these techniques are: Rapid indexing, saving of space and labor, could be performed year-round. Further experiments are underway for adaptation of the micrografting to leafroll disease and the stress method for corky-bark disease.

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Mary Jean Welser and Martin C. Goffinet

Grapevine yellows is a destructive, worldwide disease of grapevines that is caused by a phytoplasma, a bacterium-like organism that infects and disrupts the vascular system of shoots. The North American form of grapevine yellows (NAGY) has been observed in New York State since the mid-1970s and in Virginia since the mid-1990s. Symptoms duplicate those of vines suffering from an Australian disease complex known as Australian grapevine yellows (AGY). We sought to determine if infected `Chardonnay' vines have common anatomical characteristics across the three regions. At each geographic site in late summer, 2003–04, leaf and internode samples were taken from younger green regions of shoots and from mature basal regions in the fruiting zone. These were processed for histology. The anatomy of each organ type was compared between locations on the shoot, between geographic locations, and between affected and normal shoots. The phloem was the only tissue universally affected in vines with NAGY or AGY symptoms. In stem internodes, both primary phloem and secondary phloem showed many senescent cells, abnormally proliferated giant cells, and hyperplasia. In affected secondary phloem there was disruption of the radial files of cells that normally differentiate from the cambium into mature phloem cell types. Normal bands of secondary phloem fibers (“hard phloem”) in internodes were weak or absent in affected vines. Leaves also had disrupted phloem organization but near-normal xylem organization in vines with symptoms. Leaves of infected vines frequently showed a disruption of sugar transport out of the leaf blades, manifested by a heavy buildup of starch in chloroplasts of mesophyll cells and bundle-sheath cells.

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D.L. Hopkins and J.W. Harris

Screening for resistance to Elsinoe ampelina (de Bary) Shear, causal agent of grape anthracnose, in grapevine seedlings is commonly conducted by natural infection over 3 to 4 years in the vineyard. The objective of this research was to develop a greenhouse screening method for selecting grapevine seedlings with resistance to anthracnose. Spores of E. ampelina were obtained from 3- to 4-week-old cultures on potato dextrose agar. Inoculum concentrations ranging from 1.3 × 103 to 1.3 × 107 E. ampelina conidia per mL were evaluated and 106 conidia/mL was optimum. The time of incubation of seedlings in a moist chamber after inoculation varied from 24 to 120 hours with 24 to 72 hours resulting in good symptom development. Temperatures in the moist chamber from 16 to 32 °C were evaluated and the most consistent results were obtained at 20 to 28 °C. The most effective method for selecting anthracnose-resistant grape seedlings in the two-to-three true-leaf stage was misting the seedlings with a suspension containing 106 conidia/mL in water and placing the inoculated seedlings in a moist chamber at 24 °C for 48 hours, followed by 8 days on a greenhouse bench. Resistant seedlings from the greenhouse screening (those with <10 foliar lesions) were transplanted into the vineyard and found to be resistant to anthracnose infection under rainy, humid conditions. This greenhouse procedure for selecting grapevine cultivars and breeding lines with resistance to anthracnose is accurate, economical, and labor-saving.

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Ashley Basinger, Edward Hellman*, and Steven Shelby

Partial rootzone drying (PRD) and regulated deficit irrigation (RDI) were evaluated separately over two years on Vitis vinifera L. variety `Cabernet Sauvignon' for their applicability to commercial vineyards in Texas and to investigate their potential for enhancing grapevine acclimation and cold hardiness. PRD treatments compared the alternating-half-rootzone water application strategy of PRD to an equal volume of water applied to the entire rootzone and a 2× volume of water applied to the entire rootzone. RDI treatments compared the effects of deficit irrigation at different developmental stages of grapevine: post-fruit set to veraison; veraison to harvest; post-harvest; and a no-deficit control. The PRD treatment plots performed similarly to the equal volume treatment plots for yield and fruit composition. The double-volume treatment had a trend to higher yield in 2002 and statistically significant higher yields in 2003, and slightly lower soluble solids content of fruit in 2002. Thus, the two deficit treatments, PRD and Equal, experienced only a small reduction in performance while enabling reduced water usage. The PRD alternating-half-rootzone strategy demonstrated no advantage over a standard deficit irrigation strategy. Grapevines irrigated with the RDI strategy responded to this treatment most during the post-fruit set to veraison stage of development, which had lower yields and higher fruit soluble solids compared to the no-deficit treatment in 2002. Both PRD and RDI deficit irrigation strategies significantly increased the earliness and rate of periderm development on shoots in both years, but did not result in consistently greater cold hardiness compared to no-deficit treatments.

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Brandon R. Smith and Lailiang Cheng

`Concord' grapevines (Vitis labruscana Bailey) can readily develop iron deficiency-induced leaf chlorosis when grown on calcareous or high pH soils. Iron (Fe) chelates are often applied to the soil to remedy chlorosis but can vary in their stability and effectiveness at high pH. We transplanted own-rooted 1-year-old `Concord' grapevines into a peat-based medium adjusted to pH 7.5 and fertigated them with 0, 0.5, 1.0, 2.0, or 4mg·L–1 Fe from Fe-EDDHA [ferric ethylenediamine di (o-hydroxyphenylacetic) acid] to determine the effectiveness of this Fe chelate for alleviating Fe deficiency-induced chlorosis at high pH. Vines were sampled midseason for iron, chlorophyll, CO2 assimilation, and photosystem II quantum efficiency (PSII) and at the end of the season for leaf area, dry weight, and cane length. We found that leaf total Fe concentration was similar across all treatments, but active Fe (extracted with 0.1 n HCl) concentration increased as the rate of Fe-EDDHA increased. Chlorophyll concentration increased curvilinearly as applied Fe increased and was highly correlated with active Fe concentration. CO2 assimilation, stomatal conductance, and PSII were very low without any supplemental Fe and increased rapidly in response to Fe application. Total leaf area, foliar dry weight, and cane length all increased as Fe application increased to 1 mg·L–1 Fe, but above this rate, a further increase in Fe did not significantly increase growth. Our results demonstrate that Fe-EDDHA is very effective in alleviating Fe deficiency-induced leaf chlorosis in `Concord' grapevines grown at high pH, which provides a foundation for continuing research related to the optimum rate and timing of application of Fe-EDDHA in `Concord' vineyards on calcareous soils. Compared with total Fe, leaf “active Fe” better indicates the actual Fe status of `Concord' vines.

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M. McLean, S. Howell, J.A. Flore, and A.J.M. Smucker

Both berries and roots of grapevines are powerful carbohydrate sinks. However, during periods of soil-moisture stress, the relative strength of these two sinks is not known. This experiment was conducted to evaluate interrelationships between differing crop loads on carbohydrate partitioning for above and below-ground tissues. Root development, depth, and rate of turnover were determined by quantifying root images from video recordings taken to depths of 75 cm at two week intervals throughout the growing season. Two-year old own rooted Seyval grapevines, and Seyval grafted to 5-BB and Seyval, were grown under a rain exclusion shelter and provided with 10 or 2.5 liters of water/plant/week. Treatments were cropping level, either 0 or 6-clusters/vine. Shoot length, number of mature nodes, and dry leaf weight of vines under high cropping level were significantly reduced compared to vines growing under the low cropping level; so was root number and depth of root penetration. These data suggest that conditions of low soil moisture result in carbohydrate partitioning in favor of the clusters at the expense of the roots.

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Guadalupe Osorio-Acosta and Jorge Siller-Cepeda

Cane pruning of `Superior' grapevines grown on Hermosillo valley vineyards is normally done between 5 and 10 Jan., with cyanamide application right after pruning. However, hand labor to tie the canes on the wires and rainy days occurring at that time makes it difficult to apply cyanamide right after pruning, resulting in uneven budbreak. Four-year-old `Superior' grapevines were pruned on 17 Dec. (PD1) and 27 Dec. (PD2) 1994 and 6 Jan. 1995 (PD3), and hydrogen cyanamide (5% Dormex) was applied on 7 Jan. Budbreak was evaluated on three segments of the canes. Total budbreak of vines pruned on 17 Dec. was 71%, 90%, and 80% on the first, second, and third segment of the canes, while on plants pruned on 27 Dec., the response was 39%, 50%, and 79% budbreak on the three segments of the canes, respectively. On vines pruned on 6 Jan., budbreak was 71%, 79%, and 88% on the first, second, and third segment of the canes. Response on cluster number was similar to budbreak, improving when the plants were pruned early (PD1). Number of cluster on PD1, PD2, and PD3 were 7.1, 4.5, and 4.8, respectively. Cluster distribution on PD1 among the canes were 1, 2.4, and 3.7 on the first, second, and third segments; on PD2, 0.3, 2, and 2.2; and on PD3, 0.8, 2, and 2 clusters, respectively.

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D.W. Lotter, J. Granett, and A.D. Omer

Secondary infection of roots by fungal pathogens is a primary cause of vine damage in phylloxera-infested grapevines (Vitis vinifera L.). In summer and fall surveys in 1997 and 1998, grapevine root samples were taken from organically (OMVs) and conventionally managed vineyards (CMVs), all of which were phylloxera-infested. In both years, root samples from OMVs showed significantly less root necrosis caused by fungal pathogens than did samples from CMVs, averaging 9% in OMVs vs. 31% in CMVs. Phylloxera populations per 100 g of root did not differ significantly between OMVs and CMVs, although there was a trend toward higher populations in OMVs. Soil parameters, percent organic matter, total nitrogen, nitrate, and percent sand/silt/clay also did not differ significantly between the two regimes. Cultures of necrotic root tissue showed significantly higher levels of the beneficial fungus Trichoderma in OMVs in 1997 but not in 1998, and there were significantly higher levels of the pathogens Fusarium oxysporum and Cylindrocarpon sp. in CMVs in 1998 but not in 1997. Implications for further research and for viticulture are discussed.

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Sanliang Gu, Porter B. Lombard, and Steven F. Price

One- and two-year-old `Pinot noir' grapevines were irrigated with Hoagland's nutrient solution and shaded with 60% shade cloth to investigate the effect of shading on inflorescence necrosis (IN), tissue ammonium, and nitrate status. Shading increased IN, tissue ammonium, and nitrate concentrations of laminas, petioles, and rachis in two-year-old vines. IN was positively correlated with tissue ammonium and nitrate levels. In one-year-old vines, tissue ammonium and nitrate concentrations were increased by shading in most tissues except for nitrate in tendrils and old roots. Tissue ammonium correlated with nitrate concentration in various tissues after anthesis in one-year-old vines and in laminas, petioles, fruit, and rachis of two-year-old vines. Elevated tissue ammonium in rachis has been suggested as a possible cause of IN.

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Martin L. Kaps and Marilyn B. Odneal

`Seyval blanc' and `Vidal blanc' grapevines were planted in 1983 at in-row spacings of 1.8, 2.4, 3.0, 3.6 and 4.8 m. Vineyard location is in the southcentral Missouri Ozark region, an area characterized by shallow soil and fluctuating winter temperature. A temperature of -28°C in January 1985 severely damaged the vines, which required retraining from the roots. Less time was needed to retrain close spaced vines to a single curtain cordon. Close spaced vines also yielded more in their first production year (1987). Wide spaced vines had increasingly higher pruning weight, yield, and cluster number per vine in later years. Juice soluble solids, pH and titratable acidity showed few differences among the spacing treatments. Close spaced vines were the most productive on a per meter of cordon basis. Competition between these vines has not yet reduced their productivity.