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Jorge Siller-Cepeda and Guadalupe Osorio

Grapevines growing under our desert conditions have inadecuate chilling accumulation and require dormancy-breaking chemicals to induce uniform and early budbreak. Depending on concentration and application date, this treatments could delay or damage rather than accelerate bud development. We evaluated the budbreak response of `Perlette' grapevines to hydrogen cyanamide after different chill units (CU) were accumulated. Cyanamide (0.0, 0.025, 0.050, 0.100, 0.200, and 0.400 M) were applied to single node cuttings every 50 CU. After treatments, the cuttings were placed in a warm, long day greenhouse with additional light. Budbreak was recorded every 2 days, and final percentage budbreak was determined after 3 weeks. Cyanamide broke dormancy 10 to 14 days after application. All cyanamide treatments induced 60% budbreak above the control when applied before any chilling accumulation. Highest percent of budbreak of untreated cuttings occurred after 150 CU were accumulated. Concentrations in the range from 0.1 to 0.4 M were best for overcoming dormancy. Optimum concentration varied depending on the CU accumulated before treatments.

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Guadalupe Osorio-Acosta and Jorge Siller-Cepeda

Table grapes growing under desert conditions present a short and shallow rest mainly due to low chilling and high daily temperatures. Results using Evaporative Cooling (EC) have shown that rest is modified, and the opening of primary buds and number of clusters per plant depended on pruning date and cyanamide rate. From Oct 26 until Dec 30, rest depth was assessed under lab conditions on `Flame Seedless' canes from EC-treated and control vines. We found that rest depth was shallow and final budbreak was higher in EC-treated plants at all sampling dates. However, hydrogen cyanamide treated canes under both conditions showed no difference on final budbreak, although the opening of primary buds was higher on the EC-treated plants. Field trials were established to quantify the effect of pruning date associated with those treatments (EC and Control) on the number of clusters per plant. Plants were pruned on Dec 14, Dec 22, and Dec 30, and cyanamide (5% Dormex) was applied immediately. Plants under EC conditions and pruned on the earliest dates enhanced the number of cluster per vine by 40 and 21.7% respectively, as compared with control plants.

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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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Guadalupe Osorio-Acosta, Jorge Siller-Cepeda, and Jorge Avlos

In the Sonoran desert, vines are forced to break with early pruning and cyanamide application. Usually topping of the canes (leaving canes 50 cm long) is done on 10 Dec. to facilitate spur pruning and cyanamide application after 20 Dec. However, budbreak is irregular over the years. There is no reason why date and intensity of topping is done that way. The objective of this work was to evaluate budbreak at different dates and intensity of topping. Five-year-old `Flame Seedless' vines were prune topped on three dates (21 Nov., 1 Dec., and 11 Dec.) and at three different intensities (leaving canes 25, 50, and 75 cm long). A control block was also included without top pruning. Spur pruning and cyanamide application (Dormex 7%) was done on 24 Dec. Budbreak on canes left 50 cm long before spur pruning was 83%, 84%, and 58% on 21 Nov., 1 Dec., and 11 Dec., respectively, while nontop-pruned plants break only 58% of the buds. Number of clusters per plant in the same order were 52, 42, 39, and 26, respectively. There was an interaction of date and intensity of topping with the cluster number, since slight topping (leaving 75 cm long canes) on 1 and 11 Dec. improved the number of clusters per vine up to 47 and 60, respectively.

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Jorge H. Siller-Cepeda, Leslie Fuchigami, and Tony H. H. Chen

Many seeds of woody plants require low temperature or other treatments to overcome dormancy. Changes in catalase activity and glutathione has been proposed to be associated with the breaking of dormancy. We examined the level of glutathione and catalase activity of cherry seeds (Prunus mahaleb cv. Lambert) exposed to several dormancy breaking agents. Seeds imbibed in water for 24 hrs. were either stratified at 4°C or at 25°C for up to 12 weeks, or exposed to other dormancy breaking agents. Germination test, glutathione and catalase activity were determined weekly and/or after treatment. Analysis of levels and state of glutathione were performed by high pressure liquid chromatography (HPLC), and catalase activity was assayed spectrophotometrically. Total glutathione in dry and imbibed seeds were similar, but, ratio between the reduced and oxidized form were different. Low temperature stratification for 12 weeks increased the reduced form of glutathione six-fold, while percent germination increased up to 94%.

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Jorge H. Siller-Cepeda, Leslie Fuchigami, and Tony H. H. Chen

Many seeds of woody plants require low temperature or other treatments to overcome dormancy. Changes in catalase activity and glutathione has been proposed to be associated with the breaking of dormancy. We examined the level of glutathione and catalase activity of cherry seeds (Prunus mahaleb cv. Lambert) exposed to several dormancy breaking agents. Seeds imbibed in water for 24 hrs. were either stratified at 4°C or at 25°C for up to 12 weeks, or exposed to other dormancy breaking agents. Germination test, glutathione and catalase activity were determined weekly and/or after treatment. Analysis of levels and state of glutathione were performed by high pressure liquid chromatography (HPLC), and catalase activity was assayed spectrophotometrically. Total glutathione in dry and imbibed seeds were similar, but, ratio between the reduced and oxidized form were different. Low temperature stratification for 12 weeks increased the reduced form of glutathione six-fold, while percent germination increased up to 94%.

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Jorge Siller-Cepeda, Leslie Fuchigami, and Tony H. Chen

Glutathione content was determined in buds of peach (Prunus persica L.) trees during rest development and release. Reduced (GSH) and oxidized (GSSG) glutathione content changed with the accumulation of chill units (CU). GSH content decreased in the early phases of rest, and then increased at maximum rest. GSH content continued to increase and peaked on 1 Dec at 860 CU, and then dropped during the quiescent stage. It appears that the increase of GSH during chilling was closely associated with the breaking of rest. In contrast GSSG showed a continuous increase from Oct to Dec. Five concentrations of cyanamide were applied every 2 weeks from Oct to Dec. All cyanamide treatments depleted GSH within 12 hr followed by a large increase 24 hr after treatment. The changes in GSH content induced by cyanamide were inversely related to the concentration. The extent of GSH change was dependent on both the physiological status of the bud and the cyanamide concentration. At maximum rest, the plants were more resistant to cyanamide treatment and this coincided with the highest level of cyanamide-induced GSH.

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Jorge Siller-Cepeda, Manuel Báez, Alfonso Stichez, Alfonso A. Gardea, and Guadalupe Osorio

Crop uniformity is critical in early season table grapes, because it diminishes labor and improves chances to attain high prices. Single cyanamide applications are regularly used; however, harvest still requires several pickings. On 6 Dec. hydrogen cyanamide was applied to 4 year-old `Perlette' vines right after pruning or at different timings to advance and uniform harvest. Three rates (4, 6, and 8% Dormex) were applied as single or splitted applications. The later were made after 6, 12, 18, 24, and 48 hrs following the initial spray. The respective half rates were used in splitted applications. Our results showed that budbreak response to a single dose was 39, 71 and 93% for increasing dosages, nonetheless, buds broke unevenly. Divided rates improved both total budbreak and uniform development. However, timing between sprays also influenced the above characteristics. The best timing between applications was 6 hrs improving budbreak to 70, 75, and 100% for increasing concentrations. Since mostly primary buds broke, this also resulted in increased clusters per vine. Budbreak rates were significantly reduced when the second application was delayed by 48 hrs (30, 33, and 63% in the same order).

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Jorge H. Siller-Cepeda, Leslie H. Fuchigami, and Tony H.H. Chen

The effects of hydrogen cyanamide (H2CN2) on budbreak and phytotoxicity of l-year-old potted peach trees [Prunus persica (L.) Batsch. cv. Redhaven] over a wide range of concentrations at several stages of dormancy were studied. Endodormancy (180° GS; degree growth stage) began on 1 Oct. Maximum intensity of endodormancy (270° GS) was reached after the plants were exposed to 320 chill units on 1 Nov., and 50% of the buds were broken at 860 chill units on 1 Dec. Five concentrations of H2C N2 (0, 0.125, 0.25, 0.5, and 1.0 m) were applied on 1 and 15 Oct., 1 and 15 Nov., and 1 and 15 Dec. 1990. All concentrations promoted budbreak; however, percent budbreak and phytotoxicity depended on concentration and timing of application. The most effective concentration (greatest budbreak and lowest phytotoxicity) was 0.125 m H2CN2 on all treatment dates. Phytotoxicity was evident at all application dates but was greatest at the highest concentrations. Plants were most resistant to H2CN2 at maximum intensity of endodormancy. Hydrogen cyanamide-induced budbreak was highest during the later stages of endodormancy (295 to 315° GS). Treatments applied during the ecodormancy stage (340° GS) inhibited and delayed budbreak and damaged buds and stems. Chemical name used: hydrogen cyanamide (H2CN2, Dormex).

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Jorge Siller-Cepeda, Alfonso Sánchez, Francisco Vázquez, Manuel Báez, René Palacios, Elsa Bringas, Evelia Araiza, and Reginaldo Báez

A rapid and sensitive high performance liquid chromatography method for quantifying simultaneously sucrose, fructose and glucose in fruits and vegetables is reported. Samples were extracted in 95% ethanol, homogenized and treated at 95C for 20 min. The supernatant was stored at -20C overnight and filtered through a G-25 Sephadex column. Aliquots were evaporated, redissolved in water, filtered, and injected. A Sorbex NH2 column operated at room temperature was used for separations. The sugars were detected at 192 nm. The retention times were 4.8, 5.9 and 10.3 min for fructose, glucose and sucrose, respectively. The method was applied to twenty-one fruit and vegetable species with different maturity stages. In addition, quality characteristics such as firmness, pH, acidity, soluble solids and color were evaluated. Main sugars for the different samples varied among species. In temperate fruits, fructose and glucose were the predominant sugars, while in tropical and subtropical fruits, the main sugar was sucrose. On the sampled vegetables, fructose was the primary sugar, although at very low levels. Quality characteristics coincided with sugar levels found among the different species.