Chilling Hours Research Articles

Application of Ethephon Manually or via Drone Enforces Bud Dormancy and Enhances Flowering Response to Chilling in Litchi (Litchi chinensis Sonn.)

Ethephon (2-chloroethylphosphonic acid) is frequently used for flush management in order to maximize flowering in litchi. However, the optimal dosage of ethephon, which balances between flush control effect and the detrimental effect on leaves, is unknown. This study aimed to identify the optimal ethephon dosage and test more efficient ethephon application methods, using a drone for flush control and flowering promotion in litchi. The effects of a single manual full-tree spray of 250, 500 or 1000 mg/L of ethephon in early November on the bud break rate, leaf drop rate, net photosynthetic rate, LcFT1 expression and floral induction (panicle emergence rate and panicle number) in ‘Jingganghongnuo’ litchi were examined in the season of 2021–2022. In the season of 2022–2023, the effects of drone application of 1000 mg/L of ethephon in early November on bud growth and floral induction were observed. The results showed that the manual ethephon treatments were effective at enforcing bud dormancy and elongating the dormancy period and that the effects were positively dependent on dosage. One manual spray of 1000 mg/L of ethephon in late autumn enabled a dormancy period of 6 weeks. The treatments advanced seasonal abscission of old leaves in winter and caused short-term suppression on photosynthesis within 2 weeks after treatment. Ethephon treatments, especially at 1000 mg/L, enhanced the expression of LcFT1 in the mature leaves and promoted floral induction reflected by earlier panicle emergence and increased panicle emergence rate and number in the terminal shoot. The floral promotion effect was also positively dosage dependent. The cumulative chilling hours below 15 °C from the date of treatment to the occurrence of a 20% panicle emergence rate were lowered in ethephon treatments. A drone spray of 1000 mg/L of ethephon solution consumed a sixth of the manual spray solution volume and was two thirds less effective in suppressing bud break compared with manual spraying. However, it achieved a significant flowering promotion effect comparable to traditional manual spraying. The results suggest that ethephon application enhanced flowering responsiveness to chilling as well as enforced bud dormancy. The application of ethephon with a drone proved to be an efficient method for flush control and flower promotion.

Chilling or chemical induction of dormancy release in blackcurrant (Ribes nigrum) buds is associated with characteristic shifts in metabolite profiles.

This study reveals striking differences in the content and composition of hydrophilic and lipophilic compounds in blackcurrant buds (Ribes nigrum L., cv. Ben Klibreck) resulting from winter chill or chemical dormancy release following treatment with ERGER, a biostimulant used to promote uniform bud break. Buds exposed to high winter chill exhibited widespread shifts in metabolite profiles relative to buds that experience winter chill by growth under plastic. Specifically, extensive chilling resulted in significant reductions in storage lipids and phospholipids, and increases in galactolipids relative to buds that experienced lower chill. Similarly, buds exposed to greater chill exhibited higher levels of many amino acids and dipeptides, and nucleotides and nucleotide phosphates than those exposed to lower chilling hours. Low chill buds (IN) subjected to ERGER treatment exhibited shifts in metabolite profiles similar to those resembling high chill buds that were evident as soon as 3 days after treatment. We hypothesise that chilling induces a metabolic shift which primes bud outgrowth by mobilising lipophilic energy reserves, enhancing phosphate availability by switching from membrane phospholipids to galactolipids and enhancing the availability of free amino acids for de novo protein synthesis by increasing protein turnover. Our results additionally suggest that ERGER acts at least in part by priming metabolism for bud outgrowth. Finally, the metabolic differences presented highlight the potential for developing biochemical markers for dormancy status providing an alternative to time-consuming forcing experiments.

Genetic and molecular regulation of chilling requirements in pear: breeding for climate change resilience.

Pear (Pyrus spp.) is a deciduous fruit tree that requires exposure to sufficient chilling hours during the winter to establish dormancy, followed by favorable heat conditions during the spring for normal vegetative and floral budbreak. In contrast to most temperate woody species, apples and pears of the Rosaceae family are insensitive to photoperiod, and low temperature is the major factor that induces growth cessation and dormancy. Most European pear (Pyrus Communis L.) cultivars need to be grown in regions with high chilling unit (CU) accumulation to ensure early vegetative budbreak. Adequate vegetative budbreak time will ensure suitable metabolite accumulation, such as sugars, to support fruit set and vegetative development, providing the necessary metabolites for optimal fruit set and development. Many regions that were suitable for pear production suffer from a reduction in CU accumulation. According to climate prediction models, many temperate regions currently suitable for pear cultivation will experience a similar accumulation of CUs as observed in Mediterranean regions. Consequently, the Mediterranean region can serve as a suitable location for conducting pear breeding trials aimed at developing cultivars that will thrive in temperate regions in the decades to come. Due to recent climatic changes, bud dormancy attracts more attention, and several studies have been carried out aiming to discover the genetic and physiological factors associated with dormancy in deciduous fruit trees, including pears, along with their related biosynthetic pathways. In this review, current knowledge of the genetic mechanisms associated with bud dormancy in European pear and other Pyrus species is summarized, along with metabolites and physiological factors affecting dormancy establishment and release and chilling requirement determination. The genetic and physiological insights gained into the factors regulating pear dormancy phase transition and determining chilling requirements can accelerate the development of new pear cultivars better suited to both current and predicted future climatic conditions.

Perspectives on the adaptation of Japanese plum-type cultivars to reduced winter chilling in two regions of Spain.

Japanese plum, like other temperate fruit tree species, has cultivar-specific temperature requirements during dormancy for proper flowering. Knowing the temperature requirements of this species is of increasing interest due to the great genetic variability that exists among the available Japanese plum-type cultivars, since most of them are interspecific hybrids. The reduction of winter chilling caused by climate change is threatening their cultivation in many regions. In this work, the adaptation perspectives of 21 Japanese plum-type cultivars were analyzed in two of the main plum-growing regions in Spain, Badajoz and Zaragoza, to future climate conditions. Endodormancy release for subsequent estimation of chilling and heat requirements was determined through empirical experiments conducted during dormancy at least over two years. Chill requirements were calculated using three models [chilling hours (CH), chilling units (CU) and chilling portions (CP)] and heat requirements using growing degree hours (GDH). Chilling requirements ranged 277-851 CH, 412-1,030 CU and 26-51 CP, and heat requirements ranged from 4,343 to 9,525 GDH. The potential adaption of the cultivars to future warmer conditions in both regions was assessed using climate projections under two Representative Concentration Pathways (RCP), RCP4.5 (effective reduction of greenhouse gas emissions) and RCP8.5 (continuous increase in greenhouse gas emissions), in two time horizons, from the middle to the end of 21st century, with temperature projections from 15 Global Climate Models. The probability of satisfying the estimated cultivar-specific chilling requirements in Badajoz was lower than in Zaragoza, because of the lower chill availability predicted. In this region, the cultivars analyzed herein may have limited cultivation because the predicted reduction in winter chill may result in the chilling requirements not being successfully fulfilled.

Estimating Chilling and Growing Degree Hours Related to Deciduous Fruit Production in Kurdistan Region-Iraq

This study was carried out to estimate the annual chilling and heat accumulation in Kurdistan region-Iraq using three different models; chilling hours (CH), chilling units (CU) and chilling portions (CP), as well as estimating the accumulated growing degree hours (GDH) using the ChillR Package, Version 0.72.8 based on daily maxima and minima temperatures of 170 locations for 40 years (1983-2022) downloaded from NASA. The results showed that in Kurdistan region, the chilling hours with 7 classes ranged from 335 CH in Shahreban (Diyala) to 1083 CH in Amedi, Deraluk, Dinarte, Kani Masi, and Shiladize (Duhok), and Barzan (Erbil), with an average of 886 CH. The chilling units (CU, Utah Model) with 6 classes ranged from 507 CU (Shahreban, Diyala) to 1135 CU (Hizawa, Duhok), with an average of 927 CU. However, the chilling portions with 7 classes ranged from 30.0 CP in Shahreban to 58.3 CP in Ahmad Awa, Khurmal, Penjwin, Sirwan, and Zalm (Salaymaniyah), with an average of 49.5 CP. Growing degree hours with 7 classes ranged from 1136 GDH Choman, Galala, Haji Omaran and Samilan (Erbil) to 8564 GDH in Shahreban, with an average of 3256 GDH. All models were strongly correlated with location parameters, the highest strong correlations were found between each CP and GDH with AAT. The observations emphasized that both CU and CP models are more accurate than CH model for estimation of chilling and growing degree hours (units) in Kurdistan region-Iraq.

Temperature Trends and Accumulation of Chill Hours, Chill Units, and Chill Portions in South Carolina

Temperature Trends and Accumulation of Chill Hours, Chill Units, and Chill Portions in South Carolina

Overcoming dormancy of pecan trees in mild winter conditions

This study aimed to determine chill accumulation to overcome endodormancy of pecan trees using the biological method. Cuttings of isolated nodes in different months and their exposure to natural chill under field conditions were used. The experiment was carried out using seven pecan cultivars: Barton, Mohawk, Jackson, Success, Desirable, Farley and Melhorada (Pitol 1), planted in orchards in the municipality of Canguçu, Rio Grande do Sul, Brazil. Every 30 days from June onwards, when 50% of leaves had fallen from trees (phenological stage 95), 20 cuttings per cultivar were collected in each period untill September. They were sterilized and sent to the phytotron for budbreak monitoring. Budbreak average time, time to reach 50% of budbreak and the final budbreak rate were evaluated. Average budbreak time of cultivars showed little variation along collection period. Chill requirement of pecan cultivars ranged from 51 to 369 chill hours (below 7.2 °C) to reach DD50. It was not possible to determine the chill requirement of the studied cultivars. The moment of cutting collection had little influence on average budbreak time and final budbreak rate.

The influence of chilling hours on root starch content, growth and yield of strawberry tray plants

The chilling requirements of two strawberry cultivars (‘Sonata’, ‘Albion’) were assessed by evaluating the starch accumulation levels in the tray plants’ root system and their subsequent growth and yielding. The research was conducted in an experimental orchard and a greenhouse of the National Institute of Horticultural Research in Skierniewice, Poland, in 2017–2019 (2 cycles of obtaining planting material and growing plants). The tray plants (rooted tips) were grown in the natural field conditions until they were transferred in batches to a cold store (–2°C) on five different dates: 12 Oct., 30 Oct., 20 Nov., 11 Dec., and 3 Jan. (of the following year). The number of accumulated chilling hours less than 7°C was recorded for each transfer date, and the roots were analysed for starch content at the time of transfer. After the end of cold storage (3 months, standardised for all treatments), the plants were planted in pots and transferred to a greenhouse to assess growth and plant yielding. The obtained results indicate that chilling induces changes in the extent of starch accumulation. The highest starch accumulation in ‘Sonata’ roots was recorded when the plants received about 500 h of chilling (under Polish conditions accumulated in November/December). In the ‘Albion’ strawberry case, the maximum was found at the lower chilling level – about 300 h (middle of November). The highest fruit yields were produced by ‘Sonata’ plants, for which the number of chilling hours (0–7°C) was 500–800 h. In the case of ‘Albion’, the values were 2–3 times lower. A more extended period of keeping tray plants in field conditions (over 1000 h of chilling) resulted in a deterioration in fruit yield.

Multiple transcriptome comparisons reveal the essential roles of FLOWERING LOCUS T in floral initiation and SOC1 and SVP in floral activation in blueberry.

The flowering mechanisms, especially chilling requirement-regulated flowering, in deciduous woody crops remain to be elucidated. Flower buds of northern highbush blueberry cultivar Aurora require approximately 1,000 chilling hours to bloom. Overexpression of a blueberry FLOWERING LOCUS T (VcFT) enabled precocious flowering of transgenic "Aurora" mainly in non-terminated apical buds during flower bud formation, meanwhile, most of the mature flower buds could not break until they received enough chilling hours. In this study, we highlighted two groups of differentially expressed genes (DEGs) in flower buds caused by VcFT overexpression (VcFT-OX) and full chilling. We compared the two groups of DEGs with a focus on flowering pathway genes. We found: 1) In non-chilled flower buds, VcFT-OX drove a high VcFT expression and repressed expression of a major MADS-box gene, blueberry SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (VcSOC1) resulting an increased VcFT/VcSOC1 expression ratio; 2) In fully chilled flower buds that are ready to break, the chilling upregulated VcSOC1 expression in non-transgenic "Aurora" and repressed VcFT expression in VcFT-OX "Aurora", and each resulted in a decreased ratio of VcFT to VcSOC1; additionally, expression of a blueberry SHORT VEGETATIVE PHASE (VcSVP) was upregulated in chilled flower buds of both transgenic and non-transgenic' "Aurora". Together with additional analysis of VcFT and VcSOC1 in the transcriptome data of other genotypes and tissues, we provide evidence to support that VcFT expression plays a significant role in promoting floral initiation and that VcSOC1 expression is a key floral activator. We thus propose a new hypothesis on blueberry flowering mechanism, of which the ratios of VcFT-to-VcSOC1 at transcript levels in the flowering pathways determine flower bud formation and bud breaking. Generally, an increased VcFT/VcSOC1 ratio or increased VcSOC1 in leaf promotes precocious flowering and flower bud formation, and a decreased VcFT/VcSOC1 ratio with increased VcSOC1 in fully chilled flower buds contributes to flower bud breaking.

Assessing Phenological Shifts of Deciduous Forests in Turkey under Climate Change: An Assessment for Fagus orientalis with Daily MODIS Data for 19 Years

Understanding how natural ecosystems are and will be responding to climate change is one of the primary goals of ecological research. Plant phenology is accepted as one of the most sensitive bioindicators of climate change due to its strong interactions with climate dynamics, and a vast number of studies from all around the world present evidence considering phenological shifts as a response to climatic changes. Land surface phenology (LSP) is also a valuable tool in the absence of observational phenology data for monitoring the aforementioned shift responses. Our aim was to investigate the phenological shifts of Fagus orientalis forests in Turkey by means of daily MODIS surface reflectance data (MOD09GA) for the period between 2002 and 2020. The normalized difference vegetation index (NDVI) was calculated for the entire Turkey extent. This extent was then masked for F. orientalis. These “Fagus pixels” were then filtered by a minimum of 80% spatial and an annual 20% temporal coverage. A combination of two methods was applied to the time series for smoothing and reconstruction and the start of season (SOS), end of season, and length of season parameters were extracted. Trends in these parameters over the 19-year period were analyzed. The results were in concert with the commonly reported earlier SOS pattern, by a Sen’s slope of −0.8 days year−1. Lastly, the relationships between SOS and mean, maximum and minimum temperature, growing degree days (GDD), and chilling hours (CH) were investigated. Results showed that the most significant correlations were found between the mean SOS trend and accumulated CH and accumulated GDD with a base temperature of 2 °C, both for the February–March interval. The immediate need for a phenological observation network in Turkey and its region is discussed.

Climate trends of a typical apple growing mid- hill district of Himachal Pradesh.

For four sample decades, the study examined the long-term climate trends along with the area and production changes in Chamba district of Himachal Pradesh. A database was collected for maximum temperature (Tmax ), minimum temperature (Tmin), and rainfall, and for the area and production of apple for the four representative decades of Chamba region of Himachal Pradesh. It has been observed that trends indicated that temperature in this district showed an increasing trend and precipitation (rainfall) showed decreasing trend. Temperature, rainfall was the main parameters collected along with other meteorological parameters. The minimum and maximum temperature & rainfall data were collected from the records of government departments for the period of at-least 25-30 years. Long term trends were generated to check the change detection. The minimum temperature in Chamba district has shown an increase of 0.36°C and maximum temperature increase by 0.3°C and annual rainfall decreased by 117.95 mm in 36 years. It has also been observed that many farmers are now opting for industrial crops like mushroom, flowers, off season vegetables because of climate change. Due to an increase in temperature, apple crop is getting less chilling hours, which is somehow affecting the quality of fruit. More long term research efforts are required to be conducted in Free Air Temperature Enrichment (FATE) which can enhance this study. This study also indicates that there is an increase in area and production in Chamba district but fluctuation is seen in productivity. Shifting to higher elevation might be temporary solution to meet the chilling requirement but a proper measures need to be taken. The area under apple cultivation has increased substantially from a mere 400 hectares in 1950s to 11. 4 lakhs hectares in 2020s but fluctuation is observed in the productivity of the crop. Considering the vital role that apple has in the economy of Himachal Pradesh, there is a need to study the production and productivity of the apple crop

Impact of Chill and Heat Exposures under Diverse Climatic Conditions on Peach and Nectarine Flowering Phenology.

The present study aims to generalize cultivar-specific tree phenology responses to winter and spring temperatures and assess the effectiveness of the Tabuenca test and various chill and heat accumulation models in predicting bloom dates for a wide range of climatic conditions and years. To this end, we estimated the dates of rest completion and blooming and correlated them with observed bloom dates for 14 peach and nectarine cultivars that were evaluated in 11 locations across Europe (Greece, France, Italy, Romania and Spain), within the EUFRIN cultivar testing trial network. Chill accumulation varied considerably among the studied sites, ranging from 45 Chill Portions (CP) in Murcia-Torre Pacheco (Spain) to 97-98 CP in Cuneo (Italy) and Bucharest (Romania). Rest completion occurred latest or was not achieved at all for some cultivars in the southern sites in Murcia. Dormancy release happened earliest in Bucharest and Cuneo, sites where heat accumulation had a strong influence on the regulation of bloom time. Blooming occurred earliest in the moderately cold regions of Lleida (Spain) and Bellegarde (France), and 7-11 days later in the warmer locations of Rome (Italy) and Naoussa (Greece), suggesting that bloom timing is strongly influenced by delayed rest completion in these locations. The Dynamic Model resulted in both more homogeneous chill accumulation across years and better predictions of bloom dates, compared with the Utah, Positive Utah and Chilling Hours models. Prediction of bloom dates was less successful for low-chill cultivars than for medium- and high-chill cultivars. Further climatic and experimental data are needed to make estimates of the climatic needs of peach cultivars more robust and to generate reliable advice for enhancing the resilience of peach production under varying and changing climatic conditions.

Are long-term climate projections useful for on-farm adaptation decisions?

The current literature on climate services for farmers predominantly focuses on seasonal forecasts, with an assumption that longer-term climate projections may not be suitable for informing farming decisions. In this paper, we explore whether certain types of long-term climate projections may be useful for some specific types of farming decisions. Through interviews with almond tree crop farmers and farm advisors in California, we examine how farmers perceive the utility and accuracy levels of long-term climate projections and identify the types of projections that they may find useful. The interviews revealed that farmers often perceive long-term climate projections as an extension of weather forecasts, which can lead to their initial skepticism of the utility of such information. However, we also found that when farmers were presented with long-term trends or shifts in crop-specific agroclimatic metrics (such as chill hours or summer heat), they immediately perceived these as valuable for their decision-making. Hence, the manner in which long-term projections are framed, presented, and discussed with farmers can heavily influence their perception of the potential utility of such projections. The iterative conversations as part of the exploratory interview questions, served as a tool for “joint construction of meaning” of complex and ambiguous terms such as “long-term climate projections,” “long-term decisions” and “uncertainty.” This in-turn supported a joint identification (and understanding) of the types of information that can potentially be useful for on-farm adaptive decisions, where the farmer and the interviewer both improvise and iterate to find the best types of projections that fit specific decision-contexts. Overall, this research identifies both the types of long-term climate information that farmers may consider useful, and the engagement processes that are able to effectively elicit farmers' long-term information needs.

Models for Apothecial Emergence and Ascospore Discharge of Monilinia vaccinii-corymbosi in Michigan Blueberry Fields

Monilinia vaccinii-corymbosi ( Mvc) is the causal agent of mummy berry in highbush blueberries. The primary inoculum of Mvc consists of ascospores that are discharged from apothecia on overwintered mummified blueberry fruits on the ground below blueberry bushes. Models currently exist in southern climates to predict the emergence of apothecia and ascospore discharge based on growing degree days. To better understand the release of primary inoculum in northern climates, apothecial emergence and ascospore discharge were studied in relation to weather variables. A Burkard spore trap was used to collect ascospores in blueberry fields with a history of the disease in 2002, 2003, 2004, and 2009. Peak ascospore discharge was inversely correlated with daily relative humidity, and the majority of ascospores were initially discharged between 61 and 291 growing degree days (using 5.5°C base) and after 1,549 to 1,924 chill hours (above freezing) were attained. The chilling requirement of pseudosclerotia was studied by removing them at different times during the winter and allowing them to germinate in the laboratory. Additionally, the optimal average apothecial cup diameter in the field was investigated in relation to ascospore discharge (between 3 and 7 mm). Finally, we proposed a simplified degree-day model to predict apothecia emergence and ascospore discharge with apothecia emergence timings at several locations from 2007 to 2010. This information can be used to predict mummy berry apothecium emergence and ascospore discharge and could be incorporated into web-based risk modeling applications for providing growers with useful tools to improve fungicide spray timing.

Budbreak of pecan cultivars subject to artificial chill

Chill is a limiting factor in commercial production of temperate fruit due to their dormancy mechanism. Thus, knowledge of chill requirements of cultivars is important to reach successful production. This study aimed at evaluating responses given by different pecan cultivars subject to artificial chill. Pecan branches were collected from twelve 9-year-old cultivars – Success, Shoshoni, Farley, Elliott, Mohawk, Jackson, Desirable, Barton, Importada, Shawnee, Choctaw and Melhorada – in two orchards located in Canguçu, Rio Grande do Sul (RS) state, Brazil, in 2017 and 2018. Treatments consisted in exposing branches to 0, 250, 500, 750 and 1,000 chill hours in a cold chamber (4.0 ± 0.5 °C) and then taking them to the germination chamber (25 ± 0.5 °C and photoperiod of 16 hours of light) until the end of the evaluations. Final budbreak rate (FBR) of every cultivar and the number of days required to reach 50% of budbreak (DD50%) were evaluated. Chill required by cultivars to start budbreak varied in both years under evaluation. Both FBR and DD50 were higher in 2017 than in 2018. Due to high variation in FBR and DD50, chill requirements of pecan cultivars could not be clearly determined by the biological method.

Adaptability and phenotypic stability of apple cultivars in a subtropical climate

ABSTRACT Breeding programmes have selected cultivars with a lower chill requirement. Apple production in these regions is socioeconomically valuable since fruit is harvested earlier than cooler regions. Understanding the adaptability and phenotypic stability in subtropical climate regions across multiple cropping seasons is important to ensure high productivity. The aim here was to evaluate the adaptability and phenotypic stability of seven apple cultivars that have been selected for a subtropical climate region. Phenology and productivity was measured including the mean number of fruit per plant, fruit weight, production per plant, mean estimated yield, and sum of chill hours, from four production cycles. Fruit quality was assessed for fruit from two production cycles. The genotype × environment interaction was analysed by the GGE biplot method. The Z selection index, the seasonal variation contributed significantly to the performance of each cultivar. Eva had the highest accumulated yield during the four production cycles and Imperatriz and Gala, had the lowest yields. Chilling requirements were the lowest for the cultivars Princesa, Eva and Julieta. Eva, Princesa and Julieta were the most stable for yield and also for the Z index. Eva and Julieta were the most adaptable and stable in subtropical climate regions.

Long-term response planting method on wheat under conservation agriculture

Objective: To compare different bed planting systems: narrow beds (80 cm), wide beds (100 cm), and flat soil, on the growth and yield of wheat under conservation system.
 Design/methodology/approach: Treatments were established on a complete block design with three replicates; also, wheat crop was grown during five seasons. Treatments were as follow: A) wide beds (furrows at 100 cm), B) narrow beds (furrows at 80 cm) and C) flat soil. Response variables were dry weight of 50 stems, weight of 1000 grains, number of spikes (m2), harvest index and yield. Also, the relationship between relative yield and cold units and degree-days were measured.
 Results: Flat soil reach the highest dry weight of 50 stems, whereas narrow beds had the maximum number of spikes per m2. Yield was equal between flat soil and narrow beds. No differences were found in the harvest index (HI) among the evaluated treatments. When comparing results between years, dry weight of 50 stems increased and the HI index decreased, affecting negatively the yield. A negative association was found between chill hours and yield.
 Findings/conclusions: Despite yield was equal between flat soil and narrow beds, reduction on yields was mainly associated with of reduction in chill hours occurring in each season.

Chilling and forcing requirement of five international fig cultivars grown in Southeastern Brazil

Chill hours availability influence break dormancy, sprouting and production of temperate fruits trees in different regions. However, there are few reports on the subject for fig tree. This study aimed to evaluate the effects of the accumulated chilling hours on the physiology and dormancy release of fig cultivars. Stem cuttings of five fig cultivars were collected at the end of winter over two crop cycles and exposed to 0, 40, 80, 120 and 160 accumulated chilling hours (CH) in a cold chamber (8±0.5 ºC). Physiology of fig buds was then evaluated with regards to antioxidant enzymes activity, carbohydrate and nitrogen contents. The exposure of fig stem cuttings with two buds to different accumulated CH presented physiological changes for antioxidant enzymes activity, carbohydrates and nitrogen contents and confirming that the cultivars responded differently to the climatic conditions of each crop cycle. Results detected that the lowest accumulated CH in field in 2018 (2.7 CH) enabled a greater effect of the artificial CH when compared to 2017 (19.5 CH). Each fig cultivar had a critical accumulation point. The cultivars Roxo de Valinhos and Pingo de Mel require less CH to break dormancy, while Troyano requires more CH to finish this vegetative rest period.

Accumulation of degree-days and chilling hours for ‘Eva’ apple tree production in temperate climate

The cultivation of apple tree is highly dependent on meteorological variables, especially temperature. The link between accumulation of degree-days (DD) and accumulation of chilling hours (CH) are determinant to field success, in the context of climate change. The objective of this study was to quantify the accumulation of DD necessary during the reproductive phenological stages for cultivar IAPAR 75 Eva, considering the accumulation of CH during the period of dormancy. The study was carried out at the Experimental Station from the Rural Development Institute of Paraná IAPAR-EMATER, in the municipality of Palmas, Paraná State, Brazil. The evaluations were from 2013 to 2019, showing for each three days, the phenological phases and the value of DD and CH. The results were submitted the simple and multiple correlation by the R® software. We verified the influence of the increase in temperature on the cycle acceleration, in addition, it was verified a tendency of less requirement for DD to advance the cultivar cycle. Were verified the value of chilling hours as 281, 156, 84, 326, 96, 76 and 11 hours of chill, respectively, and the consequent accumulation of DD to breaking dormancy was appointed as 1093, 1156, 1574, 1157, 1834, 1096 and 1838 DD, respectively. We concluded that CH causes impact in DD accumulation to development of apple tree. Higher temperatures accelerate the apple tree development. With the information of CH accumulation in dormancy, it is possible estimate the quantity of DD to develop the phenological phases. This information contributes to agricultural planning for cultivar Eva farmers

Potential Impacts of Shade Treatments on Dormancy of Overwintering Redbud (Cercis canadensis L.) Trees at Southeastern Nurseries

Abstract Dormancy accrual is an important process in mitigating the abiotic stressors of overwintering trees at ornamental nurseries, with frost-injured tree crops at heightened risk of ensuing biotic insect and disease attack. As mean global temperatures rise, overwintering nursery crops may lose dormancy earlier. Using potted eastern redbud (Cercis canadensis L.) trees placed under two types of shade cloth, under full sun, or in walk-in coolers, we measured stem, air and root zone temperatures, accrual of chill hours and mean time to bud break at two sites. While there was no significant difference between the two shade treatments, shade cloths did moderate both high and low temperatures to which trees were exposed. Differences in mean time to first bud break were observed from shaded trees versus those in full sun at each site. It may be useful to alter our shading design to continue protection from overnight lows while preventing excess warming from daytime highs, and thus promoting dormancy and preventing frost exposure in some regions, but further tests will be required. Species used in this study: eastern redbud (Cercis canadensis L.).