Percent Budbreak Research Articles

The Effect of Crop Load on Budbreak Influences Return Bloom in Alternate Bearing ‘Pixie’ Mandarin

Alternate bearing trees produce a heavy (on) crop followed by a light (off) crop. Whereas it is well documented for citrus that fruit number in the current crop inversely affects flower number in the return bloom, when in the phenology of the tree and how fruit exert an effect on floral intensity the following spring remained unresolved. ‘Pixie’ mandarin (Citrus reticulata) was used as the model system to investigate when and how fruit perpetuate cyclic differences in floral intensity. Parent shoots (current spring flush shoots) were tagged on on-crop trees and fruit were removed from individual shoots or whole trees. The number of summer and fall (summer/fall) vegetative shoots that developed on parent shoots with and without fruit and the contribution of spring shoots (floral and vegetative) made by parent shoots alone (now 1 year old) and by their summer/fall shoots to return spring bloom was quantified. Removal of fruit from individual shoots on on-crop trees in June or July had no effect on the number of flowers contributed by parent (current spring) shoots to return bloom, but increased total flower number 4-fold because summer/fall shoot number increased more than 8-fold. Removal of fruit from individual shoots of on-crop trees after July had no effect on flower number. In the whole tree experiment, parent + summer/fall shoots of off-crop trees produced more flowers the following spring than on-crop trees due to greater flower production by both parent shoots and their greater number of summer/fall shoots. Removal of all fruit in July from on-crop trees resulted in 2-fold more flowers in spring compared with off-crop trees due to the increased number of flowers contributed by both parent shoots (75% of the total) and the increased number of summer/fall shoots. The importance of summer/fall shoots to return bloom was confirmed by removing all summer/fall shoots from off-crop trees. This reduced floral intensity to that of on-crop trees. Removing all fruit from on-crop trees in December increased the percentage of budbreak in spring and flower number on parent shoots to that of off-crop trees, whereas the number of summer/fall shoots and the number of flowers the parent shoots contributed to bloom were both less than that of off-crop trees. For the branch and whole tree experiments, flower number was significantly correlated with the percentage of spring budbreak on parent + summer/fall shoots (r 2 = 0.88, P ≤ 0.0001 and r 2 = 0.71, P ≤ 0.0001; respectively). Taken together, the results of this research provide evidence that fruit of the ‘Pixie’ mandarin reduce floral intensity of the return bloom by inhibiting budbreak, which reduces summer/fall shoot growth and thus the number of nodes that can bear inflorescences and development of spring shoots, which are predominantly floral.

In Vitro Propagation of Arundinaria callosa Munro- an Edible Bamboo from Nodal Explants of Mature Plants

A procedure for in vitro propagation of Arundinaria callosa Munro has been developed. The method allows bud-break from nodal segments containing single axillary bud on Murashige and Skoog (1962) medium supplemented with different concentrations of 6- benzylaminopurine (BAP). The early bud-break was obtained in 8.9-13.3 � M BAP, within 8-15 days. The position of the node on the culm of lateral branches also affected bud-break percentage and multiplication, mid-culm nodes are the most suitable. The optimal concentration of 13.3 � M BAP is found significant for shoot multiplication. Addition of 1.0 � M 3- indolebutyric acid (IBA) enhances the shoot multiplication rate. In vitro rooting was induced when 15 � M IBA was incorporated for three subcultures in the shoot proliferation medium, was transferred tostrength MS containing 25� M IBA and 0.05 � M BAP, and finally withdrawn from the rooting medium. The regenerants were successfully transplanted into a soil mixture for acclimatization before field planting.

The effect of chilling, defoliation and hydrogen cyanamide on dormancy release, bud break and fruiting of Anna apple cultivar

The effect of defoliation (DEF) alone or combined with hydrogen cyanamide (HC) on dormancy state, fruit quality and yield of Anna apple cultivar was studied. Trees were manually defoliated on three successive dates, November 15th, December 1st and December 15th. The flower buds (FB) entered the endodormancy synchronized with vegetative buds (VB) for most of the treatments. Most of the treatments terminated endodormancy between January 27th and February 8th during the season 2004/2005 and between January 18th and February 8th during the season 2005/2006. The treatments were effective in dormancy release of FB and somewhat with VB. Defoliation on November 15th + HC recorded the lowest chilling accumulation needed to reach 50% bud break. All the treatments exceeded the control considering the percentage of flower (FBB) and vegetative bud break (VBB) either in the lab or at the field. Growing degree hours and the number of days required to reach each stage of fruiting were differed between the two studied seasons. The control and DEF on December 15th exceeded all the treatments regarding initial fruit set percentage (IFS). The defoliation treatments alone gave the highest yield (kg/tree). Defoliation + HC treatments gave the best fruit quality, while the control gave the least values.

Quebra de dormência de pereira 'Hosui' com uso de óleo mineral em dois tipos de condução

Algumas cultivares de pereira asiática, quando plantadas em regiões onde ocorrem invernos com baixo número de horas de frio, comumente apresentam deficiência e desuniformidade na brotação e floração, necessitando de meios artificiais para a quebra de dormência. Visando a miminizar esse problema, foi instalado um experimento num pomar de 4 anos de pereiras 'Hosui' (Pyrus pyrifolia), em espaçamento 4,0m x 4,0m, na Estação Experimental do Canguiri-da Universidade Federal do Paraná, no município de Pinhais-PR (latitude 25º25' sul, longitude 49º08' e altitude 920m), onde a soma de horas de frio atingiu 141 horas abaixo de 7,2ºC durante o inverno de 2005. Os tratamentos foram aplicados quando as plantas estavam no estádio fenológico A1 (gema inchada), sendo o experimento realizado em delineamento inteiramente ao acaso, com 4 repetições, em esquema fatorial 2x4x7, onde foram testados dois tipos de condução, em taça e em líder central modificado, três concentrações de óleo mineral a 4%, 6% e 8%, e uma testemunha, durante o período de agosto a novembro de 2005, e sete avaliações realizadas semanalmente pelo número de gemas em início de brotação, gemas brotadas e gemas mortas, em 4 ramos de um ano de idade e em posição inclinada, previamente marcados por planta. Os resultados obtidos mostraram que a aplicação de óleo mineral, nas concentrações de 4%, 6% e 8%, anteciparam a brotação de gemas em relação à testemunha e aumentaram a porcentagem de gemas brotadas nos dois tipos de condução, sendo que as concentrações de 6% e 8% foram mais efetivas para antecipar a brotação do que a de 4%. A porcentagem de gemas brotadas aos 84 dias após a aplicação do óleo mineral não diferiu entre os sistemas de condução, em líder central modificado e em taça.

Micropropagation of Salix pseudolasiogyne from nodal explants

The effect of phytohormones on the breaking of dormancy of axillary buds in Salix pseudolasiogyne and their subsequent proliferation from nodal explants were examined. Nodal explants obtained from a 20–year-old S. pseudolasiogyne tree were cultured either on woody plant basal medium (WPM) or WPM supplemented with benzyladenine (BA, 2.2/4.4 μM), zeatin (1.1/2.2 μM), gibberillic acid (GA3, 2.9 and 14.5 μM), and GA3 + BA (2.9 + 4.4 μM). Although axillary shoots developed in all the media, a higher percentage bud break occurred on BA supplemented media. To corroborate the results, endogenous levels of cytokinins [Cks, N 6-isopentenyladenine (iP), zeatin riboside (t-ZR), dihydrozeatinriboside (DHZR)] and abscisic acid (ABA) were determined. On BA supplemented media, the levels of zeatin type (Z-type) of Cks were higher than those of isopentenyladenine type of Ck in the explants, while the ABA level was low. Axillary shoots did not grow well and became necrotic upon subculture to fresh basal WPM. In order to improve shoot growth, they were subcultured twice at a 4-week interval on to WPM supplemented with BA (2.2/4.4 μM), GA3 (1.4 μM), or GA3 + BA (1.4 + 4.4/2.9 + 4.4 μM). Maximal shoot growth (93%) was achieved on WPM supplemented with 2.2 μM BA. Comparative analyses of endogenous Cks revealed that higher Cks (Z-type Cks) were present in actively growing shoots. Rooting was readily achieved when the shoots were subcultured to WPM without phytohormones. The rooted plants were acclimatized well upon transplantation.

A CHILLING MODEL TO ESTIMATE REST COMPLETION OF ERECT BLACKBERRIES

The time of rest completion of 'Apache', 'Arapaho', 'Chickasaw', 'Darrow', 'Kiowa', 'Navaho', and 'Shawnee' blackberry (Rubus subgenus Rubus Watson) buds was compared and various models for estimating chilling were evaluated. 'Kiowa' and 'Arapaho' buds had the shortest rest periods, while those for 'Shawnee', 'Navaho', and 'Chickasaw' buds were intermediate. 'Apache' and 'Darrow' buds had the longest rest periods. The model that ac- counted for the variation in percent budbreak among cultivars and temperatures during two dormant periods had the following two components: 1) a chilling inception temperature of -2.2 °C and 2) weighted chilling hours that accumulated after the chilling inception tempera- ture. The chilling hours in this model were weighted as follows: 0 to 9.1 °C = 1; 9.2 to12.4 °C = 0.5; 12.5 to 15.9 °C = 0; 16 to 18 °C = -0.5; >18 °C = -1. This study also elucidated that a blackberry model with a chilling inception temperature of -2.2 °C estimated chilling more accurately than one with chilling inception just after the maximum negative accumulation of chill units as used in the Utah chilling model. Also, temperatures between 0 and 2.4 °C must be weighted more heavily in a blackberry model than in the Utah peach model to ac- curately estimate chilling and rest completion. Many temperate zone fruit plants require a period of low temperatures during dormancy to grow vegetatively and produce fl owers in the spring. The number of hours necessary to fulfi ll the chilling requirement varies among fruit crops (Westwood, 1993) and cultivars (Dale et al., 2003). Several models have been used to estimate the chilling requirements and to predict the time of rest completion. In 1932, Hutchins proposed a model for peach that ac- cumulated chilling hours at temperatures ≤7 °C (Weinberger, 1950). Chandler et al. (1937) studied chilling of deciduous fruit trees, small fruit crops, and ornamentals, and Lamb (1948) examined effective chilling temperatures in 'Latham' raspberry. Both studies indicated that temperatures from 0 to 7 °C were most effective in satisfying the cold requirement. For peach, temperatures as low as 1.5 °C have been used to accumulate units in the Utah chilling model (Richardson et al., 1974), and temperatures as warm as 13 °C have been used to accumulate units in chilling models in Israel (Erez et al., 1990). As temperatures increase to 10 °C, about twice as many hours are required for rest completion of peach than at 6 o

Respiratory response of apple buds treated with budbreaking agents

Isothermal calorimetry was used to evaluate the effect of budbreaking agents (BBA) on metabolic rates R q and R C O 2 , metabolic efficiency ( R q / R C O 2 ) and specific growth rate ( R SG·Δ H B) in apple flower buds during late winter. Three BBA were tested (hydrogen cyanamide, HC at 1.0% (v/v); thidiazuron (1-phenyl-3-(1,2,3-thiadiazol-5-yl)urea), TDZ at 0.3% (v/v) and mineral oil, MO at 1% (v/v)). Water was used as a control. BBA application was performed at two R q rates (4.8 and 5.3 μW mg −1 dw, corresponding to 30 and 15 days before budbreak, approximately). R q, R C O 2 , R q / R C O 2 and R SG·Δ H B were measured during 18 days at 3 day intervals under forcing conditions. Budbreak percentage was scored at the end of the experiment. Significant differences in the calorimetric parameters ( p ≤ 0.05) were found between BBA treatment and BBA application date. The highest R q (11.4 μW mg −1 dw), R C O 2 (32.2 mmol CO 2 mg −1 dw), R SG·Δ H B (2.8 μW mg −1 dw) and budbreak percentage (95%) values were found for HC treated buds when application was performed 15 days before budbreak. These samples showed the lowest R q / R C O 2 value (368 kJ mol −1) confirming an increase in bud metabolic efficiency. These results indicate that HC is an effective BBA to overcome blooming problems associated with insufficient winter chilling on apples.

Influence of different temperatures on bud break and 1-aminocyclopropane-1-carboxylic acid content of young peach trees

Effects of different temperatures on bud break and 1-aminocyclopropane-1-carboxylic acid (ACC) content were determined by using potted two-year-old ‘Akatsuki’ peach trees. One group of trees were subjected to 1°C for four weeks and then transferred to a growth chamber at 24°C, while the other was kept at 24 °C throughout the experiment. After four-week temperature treatments floral and vegetative bud break were evaluated weekly and bud break percentage was calculated. Bud break was greater under 1 °C than 24 °C in both November and December. The time required to release buds from dormancy was shorter in December than November. In November ACC content in peach buds increased after one and two weeks, then decreased in the forth week under both treatments. However, in December ACC content after two and four weeks showed a similar trend under 1 °C and a reverse trend under 24 °C. It was higher under low temperature treatment. These data indicate that chilling requirements for bud break of peach seems to be associated with the promotion of ethylene biosynthesis caused by low temperature stress.

CHILLING REQUIREMENTS OF SELECTED FLORICANE AND PRIMOCANE-FRUITING BLACKBERRIES

The chilling requirements of the University of Arkansas blackberry cultivars Apache, Ouachita, and Prime-Jim*, and the primocane-fruiting selections APF-25, APF-27, APF-40, APF-42, APF-44, APF-46, APF-52, and APF-53 were investigated using stem cuttings from field-grown plants. A biophenometer was used to measure chilling (hours below 7 °C) in the field and 12-node cuttings of lateral shoots were taken from the cultivars every 100 hours up to 1000 hours below 7 °C. However, only 500 chilling hours had occurred at the time of this writing, and the response of budbreak to higher chilling levels could not be reported. The cuttings were placed in a mistchamber in the greenhouse with a daylength of 16 hours and air temperature of 26–29 °C. Percent budbreak was measured weekly. The cultivar × chilling interaction was significant (P = 0.05). `Apache' and `Ouachita' showed little or no budbreak up to 500 h, indicating a higher chilling requirement. The chilling requirement of Prime-Jim was determined to be between 300 h and 400 h, and that of the APF selections appeared to be between 300 h and 500 h. The chilling requirement of APF-53 could not be determined since budbreak was consistent at all levels of chilling up to 500 h. In general, the primocane-fruiting genotypes appeared to require less chilling than floricane-fruiting `Apache' and `Ouachita', and they would therefore be more suitable for low-chill locations.

Effect of artificial chilling on the depth of endodormancy and vegetative and flower budbreak of peach and nectarine cultivars using excised shoots

Stem cuttings were obtained from 12 peach and nectarine cultivars during leaf fall, placed in plastic bags at 3.0 ± 0.1 °C to simulate 0–800 h of chilling and forced to budbreak at 20.0 ± 1.0 °C for a period of 6 weeks. Some cultivars showed high blooming and leafing without exposure to chilling; chilling enhances leafing and blooming but the percentage increment was higher in leaf buds. In general, maximum budbreak was reached with less chilling accumulation (<100–200 h) in flower buds compared with leaf buds; excessive chilling caused a reduction of the percentage budbreak in flower but not in leaf buds. Additionally, chilling modified the proportion of blooming that occurred before leafing. In non-chilled shoots, blooming occurred earlier than leafing, except in cv. ‘San Pedro 16–33’ but the proportion of blooming before leafing decreased significantly with chilling in most cases. By studying the mean time to budbreak, we conclude that the flower bud generally has a lower intensity of rest; the intensity of rest declines at a slower rate in flower than in leaf buds with chilling; flower buds had greater heat requirements than leaf buds when the chilling requirement had been covered, so that each peach cultivar had a point of critical chilling accumulation below which blooming tended to occur earlier, and above which leafing tends to occur first. Flower and leaf buds had different depths of endodormancy but similar chilling requirements in the majority of peach and nectarine cultivars studied. Finally, different varieties with similar chilling requirements showed different responses to chilling. Therefore, the cutting test measuring the response of vegetative and floral buds provides considerable information on the characterisation of the variety, compared with the sole and traditional data of chilling requirements.

A Chilling Model to Estimate Rest Completion of Erect Blackberries

The time of rest completion of `Apache', `Arapaho', `Chickasaw', `Darrow', `Kiowa', `Navaho', and `Shawnee' blackberry (Rubus subgenus Rubus Watson) buds was compared and various models for estimating chilling were evaluated. `Kiowa' and `Arapaho' buds had the shortest rest periods, while those for `Shawnee', `Navaho', and `Chickasaw' buds were intermediate. `Apache' and `Darrow' buds had the longest rest periods. The model that accounted for the variation in percent budbreak among cultivars and temperatures during two dormant periods had the following two components: 1) a chilling inception temperature of –2.2 °C and 2) weighted chilling hours that accumulated after the chilling inception temperature. The chilling hours in this model were weighted as follows: 0 to 9.1 °C = 1; 9.2 to 12.4 °C = 0.5; 12.5 to 15.9 °C = 0; 16 to 18 °C = –0.5; &gt;18 °C = –1. This study also elucidated that a blackberry model with a chilling inception temperature of –2.2 °C estimated chilling more accurately than one with chilling inception just after the maximum negative accumulation of chill units as used in the Utah chilling model. Also, temperatures between 0 and 2.4 °C must be weighted more heavily in a blackberry model than in the Utah peach model to accurately estimate chilling and rest completion.

(236) Evaluation of Styrax japonicus for Time of Budbreak and Susceptibility to Spring Freeze Damage

Japanesesnowbell(Styrax japonicus Sieb. &amp; Zucc.) is an outstanding small ornamental tree that is underutilized in the United States. Many of the cultivars of this Asian native frequently suffer spring freeze damage, especially when grown in the areas of the country that routinely experience dramatic fluctuations in late winter and early spring temperatures. The objectives of this study were to determine if there was variability within S. japonicus for time of budbreak and if this variability could be used for selecting plants with reduced susceptibility to spring freeze damage. In 1998, 224 open-pollinated seedlings were planted in the field. Percent budbreak was evaluated weekly during a 6-week period in Spring 1999 and 2000. While weather conditions varied greatly between the 2 years, there was good consistency between mean budbreak ratings in 1999 and 2000. There was a 4-week difference between the earliest and latest plants to break dormancy. Based on the 1999 and 2000 data, 28 plants were selected and propagated. A replicated trial involving these selections and three cultivars was carried out in 2002, 2003, and 2004. All of the selections broke bud later and suffered less freeze damage than `Emerald Pagoda' and `Carillon', but many performed similarly to `Pink Chimes'. Variation in height, width, caliper, and canopy shape was observed among the selections. There is an opportunity to utilize the genetic variability in S. japonicus for developing cultivars with reduced susceptibility to spring freeze damage.

CONSEQUENCES OF INSUFFICIENT WINTER CHILLING ON APPLE TREE BUD-BREAK

Temperate fruit trees cultivated in regions of mild winter conditions, show several anomalies. Such anomalies are described, in a general way, as the budbreak absence and/or flowering delay. But after budbreak, fruit trees go on displaying anomalies like: paralysis of the shoot growth, development of small leaves, development of small flat shape fruits, low rate of effective fructification and reduction of the flowering-maturation cycle. Budbreak inductors do not influence the development of new leaves, and several times they stop the growth after budbreak. Among the problems of lack of chilling, the size and shape of the fruits, the low effective fructification and formation of small leaves in the shape of rosette are those that manifest more after artificial budbreak induction. INTRODUCTION A series of anomalies occurs when apple trees are cultivated in regions of mild winter, where the chilling requirements are not satisfying. Such anomalies, regarding to budbreak and flowering, have been described by several authors (Iuchi, 2002; Black, 1953; Bulon and Faust, 1995; Skinner, 1964; Saure, 1985; Chariani and Stebbins, 1994; Petri et al., 1996). But after budbreak and flowering, others anomalies go on persisting or manifesting during the cycle of the culture, and few studies describe and suggest measures that can minimize these problems. Nee and Fuchigami (1992) suggested two different approaches for overcoming rest: exit of the dormancy and elongation of the buds. The budbreak inductors can affect only the process of exit of the dormancy. However, the budbreak inductors do not influence the second approach, which involves the growth of the axillary buds and the development of the new leaves and fruits. The aim of this work is discuss and show the principle anomalies relating to the lack of chilling observed in the south of Brazil. MATERIAL AND METHODS The experiments were carried out in Cacador and Sao Joaquim, SC, Brazil. Cacador is located at 26°46’ S latitude, at 960 meters altitude, with 1067 chilling units (North Caroline modified model, Shaltout and Unrath, 1983). Sao Joaquim is located at 28°7’  S latitude, at 1353 meters altitude, with 2025 chilling units. The parameters analyzed were budbreak percentage, leaf area, average number of leaves by fructification organs and fruit size. They were sampled in five-years-old trees. The samples were collected in 10 randomized trees and for each tree 10 buds per type of bud (small spur, medium spur, big spur and brindle) were sampled. For statistical analysis Duncan test was used. RESULTS AND DISCUSSION Considering the great variability of the cold intensity in the different growing regions in the south of Brazil (Fig. 1), a series of anomalies, relating to the lack of chilling, are observed and present different intensities according to the region and year. Proc VII on TZFTS Eds. K.K. Jindal et al Acta Hort 662, ISHS 2004

Effect of the Accumulated Effective Chilling Hours at the Pruning Time on Budbreak Table Grape on Dessertic Condition

The grape crop is important in Sonora State, Mexico, even though the grape growers have some problems that put in risk its continuity. To decide the moment of pruning time is one of the important decisions that the grower must done, because that depends partly the moment and the magnitude the budbreak appeared. The objective of this study was to determine the pruning time using the Effective Chilling Hours (ECH) obtained from the climatologic station. In a commercial lot of the Superior Seedless variety, we studied the effects of pruning at different times depending on the accumulation of ECH (150, 200, 250, 350, and 400). The ECH was calculated by adding the hours that the temperature stayed in following rank 0 °C &lt; X &lt; 10 °C, reducing the hours when the temperature was greater or equal to 25 °C. The data used to calculate this were obtained from the two climatologic stations near the lot in study. The effect in the budbreak was studied in canes and spurs. The results obtained in this study show that the final budbreak in canes as in spurs were not affected by the treatments in study and it was 76.5% and 81.8% for canes and spurs respectively. There is a direct relation (R2 = 0.94) between the ECH at pruning time and the percentage of early budbreak in the canes—from 5.6% (150 ECH) to 54.1% (400 ECH). Whereas in spurs, the early budbreak was favored when pruning is done after at least 200 ECH.

Influence of time of overhead shading on yield, fruit quality, and subsequent flowering of hardy kiwifruit, Actinidia arguta

The effect of overhead shading on yield, fruit quality, and subsequent flowering was studied in 4‐year‐old Actinidia arguta ’Ananasnaya’ vines in Oregon, United States in 1998 and 1999. Experimental vines were shaded to 45% of full sun from 14 July to 14 August, 14 July to 10 September (harvest date), or 10 September to 16 November, 1998. Control vines were not shaded. Shading treatments were not repeated in 1999. Fruit fresh and dry weight development followed a similar growth pattern in all treatments. Shading had no effect on yield per vine or fruit fresh weight, length, diameter, and % soluble solids in 1998. Shading for 2 months before harvest significantly reduced fruit dry weight in 1998. Shading in 1998 did not affect percentage of budbreak or the number of buds, shoots, or fruitful shoots per vine in 1999. However, vines that were shaded had a significantly lower percentage of fruitful shoots than unshaded vines, especially vines shaded for 2 months before harvest in 1998. Vines shaded for 2 months before harvest had 48% fewer flowers and thus less yield than unshaded vines. Percent fruit set was not significantly affected by flower number per vine or by shading in the previous season. Unshaded vines produced an average of one more cluster per shoot distally (at node 12) than vines shaded for 1 or 2 months before harvest the previous year. There was no treatment effect on fruit fresh weight, dry weight, length, diameter, seed number, or % soluble solids of marketable fruit in 1999. Results show that overhead shading, as might occur with dense canopies, did not have a large impact on fruit quality or yield in the current season, but reduced yield the following season. Overhead shading for 2 months before fruit harvest, led to the greatest reduction in flower number the following season confirming that the period before fruit harvest is an important time for flower bud evocation in this species.

Manejo de plantas madres para el cultivo in vitro de segmentos nodales del guayabo (Psidium guajava L.).

Se cultivaron in vitro segmentos nodales de guayabo recolectados de brotes de injertos adultos sobre patrones juveniles, plántulas a plena exposición solar y bajo sombra (40%), plantas adultas sin y con sombra (80%). También se cultivaron explantes de plantas adultas cultivadas en el campo bajo las siguientes condiciones: control; 60 días después de la aplicación de dormex (cianamida hidrogenada 49%) al 2% y 4%; 60 días después de poda parcial; y 75 días bajo 80% de sombra. A los 60 días de cultivo, las plántulas y plantas adultas bajo sombra produjeron 0% de explantes oscurecidos. El máximo porcentaje de explantes con brotes de yemas (PBY) (100%) se obtuvo a los 20 días en explantes de plántulas, y a los 40 días en explantes de plantas adultas bajo sombra. A los 60 días, las plantas adultas e injertadas sin sombra produjeron 35% y 40% de explantes oscurecidos, respectivamente, y 85 y 80% de explantes con brotes de yemas, respectivamente. El control registró 65% de explantes brotados; los tratamientos con dormex al 2% y 4%, 80% y 70%, respectivamente; la poda parcial, 65%. La aplicación de dormex al 2% incrementó el PBY y el porcentaje de explantes con hojas formadas comparada con los del control.

From controlled environments to field simulations: leaf area dynamics and photosynthesis of kiwifruit vines (Actinidia deliciosa).

Canopy leaf area development and daily rates of carbon acquisition of kiwifruit [Actinidia deliciosa (A.Chev.) C.F. Liang et A.R. Ferguson] vines growing in orchard conditions were modelled from mathematically-based physiological descriptions of leaf area expansion and photosynthesis of individual leaves Model drivers were temperatures and photon flux densities (PFD) measured in the orchard at 30-min intervals over the growing season. A modelling framework of shoot leaf area expansion, developed from controlled environment studies, was extended to whole vines by including canopy architectural components, such as shoot numbers, percentage budbreak and proportions of shoots in different length classes. Daily photosynthesis was modelled from rectangular hyperbolic functions determined for both sun and shade leaves and simulated from calculated light interception. Canopy leaf area, photosynthesis and PFDs within the canopy, obtained from measurements from vines grown in the orchard, were used to test the model. Close agreement occurred between the simulated and measured canopy leaf area development, and also between simulated and measured rates of photosynthesis. Total carbon acquisition over the growing season, estimated at 11 kg vine-1, compared closely with measured increments in vine biomass over the growing season. Results thus confirm the physiologically based model to be readily scalable to whole vines growing in orchard conditions.

Low-Chill Trait for Endodormancy Completion in Actinidia arguta Planch. (Sarunashi) and A. rufa Planch. (Shima-sarunashi), Indigenous Actinidia Species in Japan and their Interspecific Hybrids

Budbreak on 2-bud cuttings of Actinldia arguta and A. rufa, exposed to 200 hr of natural chilling below 7°C and additional chilling at 4°C was compared with that of kiwifruit, A. deliciosa and A. chinensis. A high percentage of budbreak occurred in A. arguta and A. rufa indicating that they have a very low chilling requirement, namely 200 hr, under natural conditions, whereas A. deliciosa cultivars required 600-800 hr or more of chilling; chilling requirement of A. chinensis was intermediate. Some interspecific hybrids also exhibited a low chilling requirement.

Predicting the date of budbreak of grapevine grown in the « Serra Gaucha » region

&lt;p style="text-align: justify;"&gt;Predicting the date of budbreak allows a more organized and rational pruning, defining lire time for winter phythosanitary treatments and, if necessary, the application of products to improve homogeneous sprouting and to increase the percentage of budbreak. The objective of the work was to validate the predicting date of grapevine budbreak model developed by Pouget, in France, for the conditions of Bento Gonçalves, state of Rio Grande do Sul, Brazil. To achieve this purpose, daily meteorological data of air minimum and maximum températures (°C), from 1984 to 1999, were taken from the agroclimatological station located near the experiment. The phenological data of 20 grapevine cultivars were obtained from the Embrapa Grape and Wine Germoplasm Active Bank. The phenological évaluations for each cultivar were performed on six grapevines conducted in a high vertical trellis and pnined in a bounded double Guyot. For each year, winter pruning and cultural practices were done in the same date for ail cultivars. This methodology is based on the effects of température on the sprouting velocity, on the relationships between the sum of températures and the number of days up to sprouting, and between the precocity coefficient of sprouting and the sum of température. To obtain these relationships, the same cultivars used by Pouget were taken into account, being the June l&lt;sup&gt;st&lt;/sup&gt; the date considered for the beginning of the sum of temperature. Results show that the methodology of Pouget may be applied either for the "Serra Gaucha" conditions, with the possibility to predict the date of sprouting with two or three weeks earlier, depending on the cultivar and on the year, which permit the grower a better winter pruning planning.&lt;/p&gt;

Brotação e fertilidade de gemas em uvas sem sementes no Vale do São Francisco

Com o objetivo de avaliar a porcentagem de brotação e índice de fertilidade de gemas de cinco variedades de uvas sem sementes em cinco diferentes datas de poda, realizou-se um experimento no Campo Experimental de Bebedouro, da Embrapa Semi-Árido, em Petrolina-PE. O delineamento experimental foi em parcelas subdivididas, constituídas por cinco variedades de uvas sem sementes como tratamentos principais e cinco diferentes épocas de poda como tratamentos secundários, utilizando-se dez repetições constituídas por uma planta. As variedades utilizadas foram Perlette, Thompson Seedless, Marroo Seedless, Catalunha e Superior Seedless, e as épocas de poda foram: 18 e 19/12/2000; 18 a 21/06/2001; 23 a 29/10/2001; 29/01 a 05/02/2002 e 08 a 12/04/2002. As variáveis estudadas foram a porcentagem de brotação e o índice de fertilidade real das gemas determinado pela razão número de cachos por número de gemas. A fertilidade real de gemas foi analisada entre a 1ª e 10ª gema da vara. Os maiores valores médios para brotação e fertilidade foram observados nas variedades Marroo Seedless e Perlette, sendo que as podas realizadas nos meses de junho de 2001 e abril de 2002 favoreceram o aumento da brotação e da fertilidade das gemas na maioria das variedades.