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The temperature dependence of dormancy breaking in plants: Mathematical analysis of a two-step model involving a cooperative transition
Abstract
A two-step model describing the thermal dependence of the dormancy breaking phenomenon is developed. The model assumes that the level of dormancy completion is proportional to the amount of a certain dormancy breaking factor which accumulates in plants by a two-step process. The first step represents a reversible process of formation of a precursor for the dormancy breaking factor at low temperatures and its destruction at high temperatures. The rate constants of this process are assumed to be dependent upon the temperature according to the Arrhenius law. The second step is an irreversible cooperative transition from the unstable precursor to a stable dormancy breaking factor. The transition is assumed to occur when a critical level of the precursor is accumulated. The two-step scheme is analysed mathematically. This model explains qualitatively the main observations on dormancy completion made under controlled temperature conditions and relates the parameters of the theory to the measurable characteristics of the system.
... A bud is under ecodormancy when the trigger for growth inhibition is external, that is, from the environment outside of the plant. In the annual growth cycle, this is mostly associated with early spring when endodormancy has been released but the bud is prevented from growing due to low environmental temperatures (Fishman et al. 1987). Once the air temperature increases sufficiently, the meristem resumes growth. ...
... This modified Utah model is known as the Positive Utah Model because it ignores any negative daily sum of higher temperatures and as a result gives higher chill unit accumulation in warm areas compared with the Utah model, but somewhat equal results in colder areas with little to no chill negation. The Dynamic Chill Model (Fishman et al. 1987) is called a "process-based" model (Luedeling 2012) where it is assumed that chill accumulation is a reversible two-step system that produces a "dormancy breaking factor" via the formation of an intermediate product when exposed to low temperatures (similar range as Utah Model). The intermediated product is thermally unstable and is reversible when exposed to heat. ...
... The intermediated product is thermally unstable and is reversible when exposed to heat. When cycled with moderate temperatures, it will fixate the accumulated chill as a chill portion and thus acknowledges the dual effect of warm temperatures (Fishman et al. 1987). The Dynamic model is believed to be a more accurate chill model (Luedeling et al. 2021) but is by far the most complex. ...
Bud dormancy is an evolutionary strategy that protects temperate fruit trees from low temperatures during winter. With adequate winter chilling, it is a process consisting of a rapid entrance phase where growth inhibition increases to a maximum and is then released via an exit phase. This progression is, however, different in areas with insufficient winter chill. In such areas, the dormancy entrance phase is protracted, and the exit phase is often incomplete. Several chill models have been designed to describe the plants’ response to chill accumulation to match cultivar and site. Although it is known that these models are less accurate in warm winter areas, their accuracy during the two dormancy phases has always been assumed equal. The aim of this study was to investigate the accuracy of four chill models during the entrance and exit phases of bud dormancy of ‘Royal Gala’ buds from two contrasting climatic areas. One-year-old shoots were collected from commercial orchards and forced to determine their bud dormancy level. Before forcing, the shoots received varied amounts of chill additional to the field chill. The bud dormancy progression was represented as joint two- or three-line models to determine the entrance and exit phases. For each phase, the dormancy level of every sample was plotted against its chill accumulation based on four chill models (Chilling Hours, Utah, Positive Utah, and Dynamic Model). Results were compared to determine the ability of each model to predict the linearity of the dormancy progression. The results indicated that although all the models were able to describe the exit phase of bud dormancy successfully, none could describe a linear entrance phase. This suggests that during the onset of dormancy, buds respond to temperature differently to what is measured by the chill models making the models unreliable when winter chill is inadequate.
... Its parameters have been incorporated in a more expansive model aimed at predicting olive oil production [38][39][40]. Others [41,42] have used a dynamic model in olives that was originally developed for bud dormancy release in peach [43,44], as described below, in which optimal CUs are obtained at temperatures of 6-8 • C. ...
... When comparing i levels between the two locations during the 2019-2020 winter, i levels were significantly higher in Matityahu compared to Rehovot in 'Barnea', 'Coratina', and 'Nabali' (Table 1). Although the dynamic model uses parameters appropriate for dormancy break in peach [43,44], it has been recently used in estimating olive flowering date [42]. Thus, we also calculated Chilling Portions based on the dynamic model (Section 4.8) for the different winters ( Table 2). ...
... For example, in a winter containing 60 h of 24 • C, the distribution of these warm hours within the winter (clustered, or spread out throughout the whole winter) is not considered in any of these models, even though the distribution of these warm hours likely does affect developmental processes. In the "dynamic model" [43,44] developed for dormancy release, the timing of warm temperature periods within the winter is taken into consideration. The parameters it contains are for peach dormancy break and not for olive flower induction; thus, the values it calvelop such a model, suited for olive flower induction, to establish how warm temperatures within the winters have or do not have an effect on CU accumulation. ...
With global warming, mean winter temperatures are predicted to increase. Therefore, understanding how warmer winters will affect the levels of olive flower induction is essential for predicting the future sustainability of olive oil production under different climactic scenarios. Here, we studied the effect of fruit load, forced drought in winter, and different winter temperature regimes on olive flower induction using several cultivars. We show the necessity of studying trees with no previous fruit load as well as provide evidence that soil water content during winter does not significantly affect the expression of an FT-encoding gene in leaves and the subsequent rate of flower induction. We collected yearly flowering data for 5 cultivars for 9 to 11 winters, altogether 48 data sets. Analyzing hourly temperatures from these winters, we made initial attempts to provide an efficient method to calculate accumulated chill units that are then correlated with the level of flower induction in olives. While the new models tested here appear to predict the positive contribution of cold temperatures, they lack in accurately predicting the reduction in cold units caused by warm temperatures occurring during winter.
... and negative for temperatures equal to or greater than 16°C (Richardson et al., 1974). The dynamic model proposes that chilling accumulation occurs in a two-phase process, in which warm temperatures can nullify the effect of previous cold temperatures, and is expressed in chilling portions (CP) (Fishman et al., 1987). On the other hand, for quantifying warm temperatures, the most used model is Growing Degree Hours (GDH). ...
... and negative for temperatures equal to or greater than 16°C (Richardson et al., 1974). The dynamic model considers that chill accumulation occurs in a two-phase process, where warm temperatures can counteract the effect of previous cold temperatures and is expressed in Chilling Portions (CP) (Fishman et al., 1987). ...
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.
... Empirical work by Amnon Erez's 153 group showed that while short heat spells have little effect, long ones strongly suppress 154 endodormancy release, even if the number of cold hours needed is met (Erez et al., 1979a(Erez et al., , 155 1979b). To address this discrepancy with previous models, a different modeling approach was 156 proposed by Fishman et al. (Fishman et al. 1987a(Fishman et al. , 1987b, called 'the dynamic model'. This the DBF is produced from its precursor, such that both the production and the degradation 162 rates of the precursor are temperature-dependent. ...
... dynamic model constructed by Fishman et al. (Fishman et al., 1987a(Fishman et al., , 1987b to account for 846 the dependence of dormancy breaking in deciduous trees on the winter temperatures. This 847 model was the first to account for the ordered sequence of temperatures, rather than the sum 848 of hours under each temperature. ...
Increasing winter temperatures jeopardize the yield of fruit trees requiring a prolonged and sufficiently cold winter to flower. Assessing the exact risk to different crop varieties is the first step in mitigating the harmful effect of climate change. Since empirically testing the impacts of many temperature scenarios is very time-consuming, quantitative predictive models could be extremely helpful in reducing the number of experiments needed. Here, we focus on olive ( Olea europaea ) – a traditional crop in the Mediterranean basin, a region expected to be severely affected by climatic change. Olive flowering and consequently yield depend on the sufficiency of cold periods and the lack of warm ones during the preceding winter. Yet, a satisfactory quantitative model forecasting its expected flowering under natural temperature conditions is still lacking. Previous models simply summed the number of ‘cold hours’ during winter, as a proxy for flowering, but exhibited only mediocre agreement with empirical flowering values, possibly because they overlooked the order of occurrence of different temperatures.
We empirically tested the effect of different temperature regimes on olive flowering intensity and flowering-gene expression. To predict flowering based on winter temperatures, we constructed a dynamic model, describing the response of a putative flowering factor to the temperature signal. The crucial ingredient in the model is an unstable intermediate, produced and degraded at temperature-dependent rates. Our model accounts not only for the number of cold and warm hours but also for their order. We used sets of empirical flowering and temperature data to fit the model parameters, applying numerical constrained optimization techniques, and successfully validated the model outcomes. Our model more accurately predicts flowering under winters with warm periods yielding low-to-moderate flowering and is more robust compared to previous models.
This model is the first step toward a practical predictive tool, applicable under various temperature conditions.
... There are several models available to estimate these agroclimatic requirements. The chill accumulation has been supported by the use of multiple models such as Chilling Hours Model by Weinberger (1950), Utah model by Richardson et al. (1974), and Dynamic Model by Fishman et al. (1987aFishman et al. ( , 1987b. Among these models, the Dynamic Model seems to be suitable for the Mediterranean climate (Ruiz et al., 2007;Luedeling, 2012;Prudencio et al., 2018;Rodríguez et al., 2021) and under Tunisian warm conditions (Elloumi et al., 2013;Ghrab et al., 2014a;Benmoussa et al., 2017a). ...
... Agroclimatic requirements were calculated as the average sum of accumulations across all years between 1996 and 2022 and were computed for each site during the respective phenology observation periods. This calculation was performed using the Dynamic Model (Fishman et al., 1987a(Fishman et al., , 1987b, and the Growing Degree Hours Model (Anderson et al., 1986). ...
Given the influence of climate change, sustain productivity of stone fruit trees is considered a major concern for growers, especially in warm areas where temperature is a crucial determinant of phenology. Sustainable fruit tree orchards depended on satisfying the chilling requirements of cultivars to trigger dormancy release and heat requirements to blossom correctly. Yet determining agroclimatic requirements are essential for predicting cultivar performance and selecting suitable production areas. To support this challenge, our study was conducted to expand the knowledge of agroclimatic requirements of cultivars of Prunus species growing in warm areas. Thus, Partial Least Squares (PLS) regression was employed to compute chilling requirements (CR) using the Dynamic Model (in Chill Portions (CP)) and heat requirements (HR) using the Growing Degree Hours Model (in (GDH)). PLS regression was employed to establish a correlation between long-term phenological observations and temperature records of 7 peach, 5 apricot, and 11 plum cultivars grown in Tunisia. The findings from the PLS regression revealed that the chilling and forcing periods appeared discontinuous. Overlaps or transition periods between the two phases were determined. For peach cultivars, the CR varied from 20 in early flowering cultivars to 63.4 CP in late flowering cultivars and the HR from 4381 to 6556 GDH. For apricot cultivars, the CR ranges from 45.3 to 47.9 CP and the HR from 5567 to 8647 GDH. For plum cultivars, the CR spans from 36.2 to 62.6 CP and the HR from 4999 to 7907 GDH. The main determinant of the flowering of the studied cultivars is the warm mean temperatures occurring during the chilling period. Our findings represent an advance regarding the global knowledge of Prunus temperature requirements which can aid in the adaptation of the stone fruit sector to climate change and mitigation of its impacts.
... Daily temperature data series from the ERA5 repository were extracted as NetCDF over a spatial window (5-20 • E and [35][36][37][38][39][40][41][42][43][44][45][46][47] • N) at a spatial resolution of 0.1 degree for the period 1985-2015, with an additional list of yearly vectors (November of the previous year to October) for the coordinates of each experimental site. For the basic processing of the temperature data series, the Climate Data Operator (CDO) was used. ...
... Overall, the CAC_GDD approach, which was based on both the single triangle method [18] and heat accumulation [23], provided more feasible results under our scattered experimental setup than the PhenoFlex model [24], which was based on the dynamic model [39] and the growing degree hours model [40,41]. The CAC_GDD approach required fewer parameters for calibration while avoiding overfitting, especially with inadequate data. ...
Abstract
Modeling phenological phases in a Mediterranean environment often implies tangible challenges to reconstructing regional trends over heterogenous areas using limited and scattered observations. The present investigation aimed to project phenological phases (i.e., sprouting, blooming, and pit hardening) for early and mid–late olive cultivars in the Mediterranean, comparing two phenological modeling approaches. Phenoflex is a rather integrated but data-demanding model, while a combined model of chill and anti-chill days and growing degree days (CAC_GDD) offers a more parsimonious and general approach in terms of data requirements for parameterization. We gathered phenological observations from nine experimental sites in Italy and temperature timeseries from the European Centre for Medium-Range Weather Forecasts, Reanalysis v5. The best performances of the CAC_GDD (RMSE: 4 days) and PhenoFlex models (RMSE: 5–9.5 days) were identified for the blooming and sprouting phases of mid–late cultivars, respectively. The CAC_GDD model was better suited to our experimental conditions for projecting pit hardening and blooming dates (correlation: 0.80 and 0.70, normalized RMSE: 0.6 and 0.8, normalized standard deviation: 0.9 and 1.0). The optimization of the principal parameters confirmed that the mid–late cultivars were more adaptable to thermal variability. The spatial distribution illustrated the near synchrony of blooming dates between the early and mid–late cultivars compared to other phases.
... For chill quantification, the Dynamic model has been identified as the most sophisticated and best-adapted model for Mediterranean climate conditions (Fernandez et al., 2020;Luedeling and Brown, 2011). This two-step model relies on the assumption that low temperatures stimulate the production of a chill precursor compound (which is not mapped to a concrete biological phenomenon), which then needs to be converted into a permanent "chill portion" -a quantification of effective chill accumulation, by a process that is most effective at moderately cold temperatures (Erez et al., 1990;Erez and Couvillon, 1987;Fishman et al., 1987). However, this model is based on a hypothetical biological process. ...
... We used the recorded temperature data to estimate chill and heat accumulation during the respective periods of investigation at both locations. Chill accumulation was computed in Chill Portions (CP), according to the Dynamic Model (Erez et al., 1990;Erez and Couvillon, 1987;Fishman et al., 1987). The Dynamic Model assumes that chill accumulation results from a two-step process, which is mediated by a thermally labile precursor (not yet identified) and it would follow the Arrhenius law that describes the mathematical relationship between temperature and the rate of a chemical reaction. ...
Temperate fruit trees are widely cultivated across the world's temperate regions. These trees are well-adapted to cold-winter climates through their ability to synchronize their phenology with the seasons. In autumn, they enter a dormant state, which allows them to survive the low winter temperatures and lasts until they resume growth in early spring. We analyzed the agroclimatic requirements (chill accumulation in Chill Portions, CP, and heat accumulation in Growing Degree Hours, GDH) for blooming in three sweet cherry cultivars ('Samba', 'Burlat', and 'Sylvia') grown in distinct climatic settings in Bonn (Germany) and Zaragoza (Spain). We used Partial Least Squares (PLS) regression analysis to relate bloom dates of the three cultivars grown in both locations to local temperatures. In Bonn, the colder location, trees experienced a long period of chill exposure (87-105 CP), which allowed a rapid growth response to warm temperatures (3233-4343 GDH). The flowering dates were mainly driven by conditions during the forcing period. In contrast, in the warmer climate of Zaragoza, chill exposure of the trees was relatively short (48-59 CP). The buds required long exposure to warm conditions (5444-6988 GDH) to subsequently bloom. In this case, flowering dates were influenced more by exposure to chilling than by conditions during the heat accumulation period. Global warming caused opposite effects on flowering dates depending on location. While in Bonn flowering dates have advanced between 3 and 5 days per decade, bloom dates in Zaragoza did not show such a trend, except for minor flowering delays in 'Sylvia', the late-flowering cultivar. Our results show that the response of the flowering dates to temperature appeared to depend on specific local climatic conditions. Although we applied current methodologies to determine the agroclimatic requirements of these cultivars, our methods were unable to derive consistent estimates of agroclimatic needs across the two locations.
... "Chilling Units" (CU) are computed using different chill effectiveness weights corresponding to various temperature ranges according to the Utah model [44]. "Chill Portions" (CP) are accumulated through a two-step process, in which a chilling precursor is formed in cool conditions and later converted to a permanent CP through a subsequent process that shows optimal effectiveness at mild temperatures, according to the Dynamic model [45]. ...
... For example, 47 European pear cultivars were experimentally analyzed in the early 1960s, grouping them into four qualitative categories but without estimates of chill requirements [50]. Another study of 45 [51]. Previous data on heat requirements are only available for 17 cultivars, among them 'Conference', which needed 4755 GDH for flowering in 1976, a lower value than our estimate (7347 ± 905 GDH) [51]. ...
Flowering in temperate fruit trees depends on the temperatures during the previous months; chill is required to overcome endodormancy, and then heat exposure is needed. These agroclimatic requirements are cultivar-specific and determine their adaptability to the growing area and their response to climate change. We aim to estimate the agroclimatic requirements of 16 traditional cultivars of European pears grown in Zaragoza (Spain). We used Partial Least Squares regression analysis to relate 20-year records of flowering dates to the temperatures of the 8 previous months. This approach allowed us to establish the chilling and forcing periods, through which we quantified temperatures with three models for chill accumulation (Chilling Hours, Utah model, and Dynamic model) and one model for heat accumulation (Growing Degree Hours). The results indicated very little difference in the chilling and forcing periods. Chill requirements ranged from 43.9 to 49.2 Chill Portions; from 1027 to 1163 Chilling Units; and from 719 to 774 Chilling Hours. Heat requirements ranged from 6514 to 7509 Growing Degree Hours. Flowering dates were mainly determined by the temperatures during the chilling period. This means that reductions in winter chill caused by global warming in many regions could cause flowering delays or even failures in the fulfillment of chill requirements.
... PLS regression analysis has emerged as a suitable statistical approach to delineate the most probable periods for chill and heat accumulation in temperate species (Luedeling et al., 2013;Luedeling and Gassner, 2012). The agroclimatic requirements are then estimated, using one or more temperature models (Fishman et al., 1987;Richardson et al., 1974;Weinberger, 1950), as the observed chill and heat during the delineated periods. ...
... The Utah model proposes the use of "Chill Units" (CU), which are computed using different chill effectiveness weights that are assigned to various temperature ranges. The Dynamic model defines the use of "Chill Portions" (CP), which accrue through a two-step process where a precursor of chill is formed under cool conditions and later converted to a permanent CP through a second process that shows optimum effectiveness at moderate temperatures (Fishman et al., 1987). ...
Traditional fruit tree cultivars are an important source of agricultural biodiversity. These genotypes are well adapted to the regions where they grow, and their fruits offer distinctive features compared to the commercial cultivars that are frequently grown. We analyzed the adaptation prospects of seven sweet cherry cultivars grown in Zaragoza (Spain) to future climate conditions. We first delineated chilling and forcing phases using Partial Least Squares (PLS) regression to correlate phenology records with daily accumulations of chill and heat during the months preceding flowering. We then calculated chill requirements using three chill models (Chilling Hours, Utah and Dynamic) and forcing requirements using one heat model (Growing Degree Hours, GDH). Results indicated that the chilling and forcing requirements ranged between 26.1 and 60.2 CP (chill portions) and from 5473 to 8030 GDH, respectively. We then assessed the cultivars' potential to adapt to a warmer future using climate projections and comparing the chill requirements with the expected chill accumulation under two global warming scenarios, RCP4.5 (effective reduction of greenhouse gas emissions) and RCP8.5 (very high greenhouse gas emissions), by two time horizons, 2050 and 2085, with temperature projections from fifteen Global Climate Models (GCM). These projections established that chill accumulation has consistently decreased over the last 30 years, but temperate trees have shown regular breaking of dormancy, bud burst and blooming. Future chill levels are expected to continue decreasing given the sustained warming trend, so there is no guarantee that sufficient winter chill will be observed in the medium to long term if the warming trend continues. For three out of the seven cultivars we analyzed, most global climate models predict medium or low risks by 2050 and 2085 under the RCP4.5 scenario. Under the RCP8.5 scenario, particularly by the end of the 21st century (i.e. 2085), four of the cultivars with high chill needs are expected to not to meet their chill requirements very often.
... "Chilling Units" (CU) are computed using different chill effectiveness weights corresponding to various temperature ranges according to the Utah model [44]. "Chill Portions" (CP) are accumulated through a two-step process, in which a chilling precursor is formed in cool conditions and later converted to a permanent CP through a subsequent process that shows optimal effectiveness at mild temperatures, according to the Dynamic model [45]. ...
... For example, 47 European pear cultivars were experimentally analyzed in the early 1960s, grouping them into four qualitative categories but without estimates of chill requirements [50]. Another study of 45 [51]. Previous data on heat requirements are only available for 17 cultivars, among them 'Conference', which needed 4755 GDH for flowering in 1976, a lower value than our estimate (7347 ± 905 GDH) [51]. ...
Flowering in temperate fruit trees depends on the temperatures during the previous months; chill is required to overcome endodormancy, and then heat exposure is needed. These agroclimatic requirements are cultivar-specific and determine their adaptability to the growing area and their response to climate change. We aim to estimate the agroclimatic requirements of 16 traditional cultivars of European pears grown in Zaragoza (Spain). We used Partial Least Squares regression analysis to relate 20-year records of flowering dates to the temperatures of the 8 previous months. This approach allowed us to establish the chilling and forcing periods, through which we quantified temperatures with three models for chill accumulation (Chilling Hours, Utah model, and Dynamic model) and one model for heat accumulation (Growing Degree Hours). The results indicated very little difference in the chilling and forcing periods. Chill requirements ranged from 43.9 to 49.2 Chill Portions; from 1027 to 1163 Chilling Units; and from 719 to 774 Chilling Hours. Heat requirements ranged from 6514 to 7509 Growing Degree Hours. Flowering dates were mainly determined by the temperatures during the chilling period. This means that reductions in winter chill caused by global warming in many regions could cause flowering delays or even failures in the fulfillment of chill requirements.
... Chilling accumulation was calculated using chillR's "chilling" function (Luedeling et al. 2013). This function calculates chill for the dynamic model (Fishman et al. 1987a(Fishman et al. , 1987b, Utah model (Richardson et al. 1974), and chilling hours model (Bennett 1949;Weinberger 1950). Chill accumulation for select dates between 1 Nov 2018 and 1 Mar 2019 are presented in Supplemental Table S1. ...
... Calculations were performed using the function "chilling". The dynamic model (measured in chill portions), the Utah model (measured in hours using differential temperature effects within a certain temperature range), and the chilling hours model (measured in hours between 0 and 7.2 C) were derived from Fishman et al. (1987aFishman et al. ( , 1987b, Richardson et al. (1974), and Bennett (1949) and Weinberger (1950) ...
In response to challenges caused by climate change, apple (Malus ×domestica) breeding programs must quickly develop more resilient cultivars. One strategy is to breed for various bloom times. Members of the genus Malus, including domesticated apple, wild species, and hybrids, exhibit striking variations in the bloom date. Although bloom time is strongly influenced by chilling requirements, other aspects of floral development in Malus and their contributions to bloom time are less known. The purpose of this study was to investigate potential connections between predormancy flower development and final bloom time in Malus species. We performed a phenological analysis of flower development in wild and domesticated apple with extreme differences in bloom time over the course of one developmental season. We tracked histological changes in the floral apex of representatives of three early-blooming Malus genotypes (M. ×domestica 'Anna' PI 280400, M. orthocarpa PI 589392, M. sylvestris PI 633824) and three late-blooming genotypes (M. angustifolia PI 589763, M. angustifolia PI 613880, M. ×domestica 'Koningszuur' PI 188517). Our study documented their floral meristem progression and organ development and expanded on current staging systems for apple flower development to describe the changes observed. The developmental trajectories of each genotype did not group according to bloom category, and we observed variations in the floral development stage at the time of dormancy onset.
... Chilling requirement was estimated using the dynamic model (Erez et al., 1990;Fishman et al., 1987), which is considered the current best practice winter chill model (Darbyshire et al., 2011;Luedeling, 2012;Luedeling & Brown, 2011) and has been used for previous global climate change assessments (Luedeling & Brown, 2011). The model calculates chill in units ("chill portions"), based on hourly temperatures. ...
... Dormancy breaking products such as calcium cyanamide (CaCN 2 ), hydrogen cyanamide (H2CN2), or DNOC/oil (dinitroo-cresol/oil emulsion) (Almond Board of Australia, 2008) have been helpful but no product can fully compensate for the absolute absence of winter chill. Their use brings associated risks of phytotoxicity (Fishman et al., 1987). ...
Temperate perennial fruit and nut trees play varying roles in world food diversity-providing edible oils and micronutrient, energy, and protein dense foods. In addition, perennials reuse significant amounts of biomass each year providing a unique resilience. But they also have a unique sensitivity to seasonal temperatures, requiring a period of dormancy for successful growing season production. This paper takes a global view of five temperate tree fruit crops-apples, cherries, almonds, olives, and grapes-and assesses the effects of future temperature changes on thermal suitability. It uses climate data from five earth system models for two CMIP6 climate scenarios and temperature-related indices of stress to indicate potential future areas where crops cannot be grown and highlight potential new suitable regions. The loss of currently suitable areas and new additions in new locations varies by scenario. In the southern hemisphere (SH), end-century (2081-2100) suitable areas under the SSP 5-8.5 scenario decline by more than 40% compared to a recent historical period (1991-2010). In the northern hemisphere (NH) suitability increases by 20% to almost 60%. With SSP1-2.6, however, the changes are much smaller with SH area declining by about 25% and NH increasing by about 10%. The results suggest substantial restructuring of global production for these crops. Essentially, climate change shifts temperature-suitable locations toward higher latitudes. In the SH, most of the historically suitable areas were already at the southern end of the landmass limiting opportunities for adaptation. If breeding efforts can bring chilling requirements for the major cultivars closer to that currently seen in some cultivars, suitable areas at the end of the century are greater, but higher summer temperatures offset the extent. The high value of fruit crops provides adaptation opportunities such as cultivar selection, canopy cooling using sprinklers, shade netting, and precision irrigation.
... The dynamic model is often used, especially in Mediterranean regions and other warm places such as California, which are characterized by warm winters. This model considers the negative effect of elevated temperatures during winter and the duration and intensity of exposure to cold temperatures (Fishman et al., 1987;Erez et al., 1988). In the context of climate change, CU accumulation is decreasing constantly, significantly impacting fruit productivity and quality (Campoy et al., 2019). ...
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.
... Commonly used CU models include the Dokoozlian model, the Richardson (Utah) model, the Infruitec model (daily positive Utah model), and the dynamic model [4][5][6][7][8]. The Dokoozlian model calculates the ratio between exposure to cold temperatures (hours < 7 • C) and cold-negating temperatures (hours > 20 • C) [4]. ...
The rest-breaking agent, hydrogen cyanamide (HC), can substitute insufficient chill unit accumulation in Vitis vinifera and induce uniform bud-break; however, due to its toxicity it is being banned. In South Africa, red seedless grapes, including V. vinifera Crimson Seedless (CS), are the largest table grape export group; therefore, replacing HC in V. vinifera CS is crucial. This study aimed to confirm the molecular triggers induced by HC and assess the bud-break-enhancing abilities of commercial plant biostimulants. Forced bud-break assay experiments using V. vinifera CS single-node cuttings and a small-scale field trial were performed. Results demonstrated that increased chill unit accumulation (CUA) reduced HC efficacy. Bud-break started between 10 and 20 days after treatment, irrespective of final CUA. The small-scale field trial found that HC 3% and biostimulants were similar to the negative control. The treatment of dormant grapevine compound buds with nitric oxide (NO), hydrogen peroxide (H 2 O 2), and hypoxia trigger dormancy release to a certain extent, supporting the molecular models proposed for HC action. NO, H 2 O 2 , and hypoxia, in combination with PBs, may potentially replace HC; however, this needs to be confirmed in future experiments.
... Chill accumulation during the different winter seasons was characterized using chill portions (Fishman et al., 1987) calculated with the chillR package (Luedeling et al., 2013) on hourly temperatures recorded on-site from September 1 st to flowering date. ...
Introduction
To avoid the negative impacts of winter unfavorable conditions for plant development, temperate trees enter a rest period called dormancy. Winter dormancy is a complex process that involves multiple signaling pathways and previous studies have suggested that transport capacity between cells and between the buds and the twig may regulate the progression throughout dormancy stages. However, the dynamics and molecular actors involved in this regulation are still poorly described in fruit trees.
Methods
Here, in order to validate the hypothesis that transport capacity regulates dormancy progression in fruit trees, we combined physiological, imaging and transcriptomic approaches to characterize molecular pathways and transport capacity during dormancy in sweet cherry (Prunus avium L.) flower buds.
Results
Our results show that transport capacity is reduced during dormancy and could be regulated by environmental signals. Moreover, we demonstrate that dormancy release is not synchronized with the transport capacity resumption but occurs when the bud is capable of growth under the influence of warmer temperatures. We highlight key genes involved in transport capacity during dormancy.
Discussion
Based on long-term observations conducted during six winter seasons, we propose hypotheses on the environmental and molecular regulation of transport capacity, in relation to dormancy and growth resumption in sweet cherry.
... Luedeling et al., 2021) incorporates two commonly used models to predict bloom dates. It uses the 211 Dynamic Model(Fishman et al., 1987) to account for chill accumulation, and the Growing Degree 212Hours Model(Anderson et al., 1985) to account for the heat accumulation. A detailed description of 213 the PhenoFlex framework can be found in(Luedeling et al., 2021), and this framework has performed 214 well in predicting flowering dates in temporal phenology series(Luedeling et al., 2021). ...
Accurately predicting flowering phenology in fruit tree orchards is crucial for timely pest and pathogen treatments and for the introduction of managed pollinators. Making predictions requires large datasets of flowering dates, which are often limited to single locations. Consequently, resulting phenology predictions are not representative across larger geographic areas. Citizen science may offer a solution to this data gap, with millions of biological records across a wide range of taxa recorded annually. Here, a new citizen science platform called “FruitWatch” is introduced, monitoring flowering dates of fruit trees in Great Britain. The objectives of this study are to assess the suitability of FruitWatch submissions to 1) detect latitudinal variation in flowering onset dates, 2) parameterize existing phenology modelling frameworks, and 3) make predictions of flowering onset dates across Great Britain for a single year.
Using data for four cultivars from 2022, linear models reveal significant latitudinal delays in flowering onset of as much as 1.49±0.63 days per degree latitude further north (Pear ‘Conference’), with significant delays also seen in Cherry ‘Stella’ (1.39±0.48 days) and Plum ‘Victoria’ (1.22±0.18 days). FruitWatch informed phenology modelling frameworks performed well for predicting flowering onset, with root-mean-square Error values of predictions from validation datasets ranging between 4.6 (‘Victoria’) and 8.0 (‘Conference’) days. The parameterized models also provided realistic flowering onset predictions across Great Britain in 2022, with earlier flowering dates predicted in warmer areas. These findings demonstrate the potential of citizen science data to offer growers cultivar- and location-specific phenology predictions to help inform orchard management.
... Loggers were placed inside a Stevenson's screen and positioned 1.5 m above the ground. The quantification of winter chill was performed according to the Chilling Hours Model (Hutchins, 1932, as cited by Weinberger, 1950), the Utah Model (Richardson et al., 1974) and the Dynamic Model (Erez et al., 1990;Fishman et al., 1987aFishman et al., , 1987b. Because there is a general consensus within the scientific community that the Dynamic Model is the most biologically plausible existing model for representing the process of chill accumulation in temperate fruit trees across most regions, particularly in warm areas (e.g., Campoy et al., 2013;Fernandez et al., 2023Fernandez et al., , 2020bLuedeling, 2012;Zhang and Taylor, 2011), we focused the discussion of results on the application of this model. ...
... Several models were suggested to quantify the amount of chilling based on measuring air temperatures. The most common are the chilling hours model [16], the Utah model that measures chilling units [17] and the dynamic model measuring chilling portions that was developed based on the results and concepts presented above [18,19]. Figure 2 presents a scheme of the dynamic model. ...
The phenomenon of dormancy and the evolutionary causes for its development are presented together with the effects of the climatic factors: temperature and light. Shade and darkness have been found to enhance bud breaking in peach. The effects of various temperatures on chilling accumulation, chilling negation and chilling enhancement are described. The way these are computed in the face of global warming is explained, using the dynamic model. When natural chilling is less than that required, there are ways of compensation, up to a certain level. Various horticultural, physical and chemical means to achieve this are described, including bending branches, reducing vegetative vigor, shading the orchard, sprinkling to reduce daytime temperature and the application of various chemicals to break dormancy. When winter chilling is markedly reduced and temperatures increase considerably, the use of dormancy avoidance is suggested in frost-free places. This technique can induce a new growing cycle by avoiding dormancy altogether. However, the best approach is to breed high-quality cultivars requiring much less chilling. Another aspect discussed in this work, independent of the chilling requirement, is the negative effect of heat spells in winter and spring on the abnormal development of flower buds, leading to a low level of the stone fruit set and a reduced yield.
... Chill Hours were calculated by accumulating temperature between 0°C and 7.2°C (Luedeling et al., 2009). Chill Portions were computed according to a dynamic model (Fishman et al., 1987a;Fishman et al., 1987b). CP is considered as a better indicator of chill than CH because the former accounts for the impact of chill cancellation due to the exposure to sudden warm temperatures in between consecutive cold days (Luedeling et al., 2009). ...
Many fruits and nuts crops in California require winter chill accumulation to break dormancy, and insufficient chill may result into delayed flowering and uneven budbreak which can impact quality and quantity of fruits. Early information on winter chill forecast can help growers prepare for a low chill year with management alternatives to alleviate some risks. This study assessed potential of state-of-the-art seasonal prediction systems to predict winter season (NDJF) chill anomaly and chill sufficiency for important specialty crops of California at different lead times. We found that it is possible to predict winter season Chill Portions category (above-normal, below-normal, normal) starting from October with 50–80% correct forecasts in the Central Valley and southern California. The anomaly correlation coefficients between model-predicted and reference winter season CP in the UKMO and ECMWF ranged from 0.5 to 0.8 in the Central Valley and above 0.7 in most of the southern California. All models were able to predict crop-specific winter season chill sufficiency from October with more than 90% accuracy for all the crops, except for the plums which was correctly predicted more than 60% of time. Results from this study might help growers to minimize risks associated with low chill.
... The chill information provided by chill models cannot be assumed to be valid across locations . In warm areas, only the Dynamic Model (Fishman et al., 1987a(Fishman et al., , 1987b is still considered accurate Elloumi et al., 2013;Pérez et al., 2008). Using this model, estimated chilling requirements were about 60 Chill Portions (CP) for the Sirora cultivar in Australia (Zhang and Taylor, 2011), 69 CP for Kerman in California (Pope et al., 2014a), and around 32 CP for Mateur, Meknessy, Red Aleppo, Ohadi and Kerman cultivars in the Sfax region in Tunisia (Benmoussa et al., 2017b). ...
The success of pistachio production depends on the best selection of female and male trees combined with perfect flowering synchronization. In warm areas, flowering is highly affected by climate change and selecting an appropriate pollinator for a female cultivar is challenging. In this study, seventeen local pistachio pollinators were under study in the arid Central Tunisian region. Bloom timing and chilling and heat requirements were determined based on 17 years of phenology records and using the Partial Least Squares (PLS) regression. Pollen production and quality were assessed. Three pollinator groups as early-, intermediate-and late-flowering ones were delineated and their median bloom dates spanned from DOY84 to DOY110, with bloom dates spread over 27 and 37 days, allowing perfect coverage of the bloom period of the female cultivar Mateur. Within the three groups, the most interesting candidates were H23a and H26a as intermediate-flowering males, H3a, H3b, H18, H23b and H26b as late-flowering ones and H30 as an early-flowering male covering the first flowers blooming. The pollen viability was high in all the studied pollinators (92-98 %). However, great differences existed in inflorescence density (in the range of 2-4) and pollen production per inflorescence (in the range of 191-424 mg). Based on flowering synchronization, the suitable ones had less variable chilling requirements in the range of 33-37 Chill Portions (CP) in warm areas against a significant variability of the heat needs (8783-17,302 GDH). This supported the key role of increased heat accumulation to compensate for the lack of chill and when chilling requirements are not fully fulfilled in warm areas until the chill threshold value of 25 CP. A significant delayed flowering period occurred for all pistachio pollinators when chill accumulation dropped below 25 CP, which may cause asynchronous flowering, leading to poor pollination. In conclusion, bloom timing and pollen production are common variables to characterize pistachio pollinators. The agroclimatic needs could be a relevant tool for planning the best combination linked to local conditions, while estimation improvement is required for warm areas. However, pistachio cultivation in warmer areas will be viable until a certain chill level. Pistachio cultivars will be able to grow, while lack of chill will be overcome with heat accumulation key role for chill compensation until a threshold of 25CP. These findings are of high interest for the warmest orchards, which will cover many important fruit-growing regions with Mediterranean climates all over the world with the expected climate change.
... The Utah Model computed "Chilling Units" (CU) using different chill effectiveness weights corresponding to various temperature ranges [45]. Finally, the Dynamic Model accumulates "Chill Portions" (CP) through a two-step process in which a chilling precursor is formed in cool conditions and later converted to a permanent CP through a subsequent process that shows optimal effectiveness at mild temperatures [46][47][48]. The calculations were conducted using chillR v.0.72.8 package [49] in the R v.4.3.0 programming environment [50]. ...
Apricot has undergone an important cultivar renewal during the last years in response to productive and commercial changes in the crop. The impact of the sharka disease (plum pox virus) prompted the release of cultivars resistant/tolerant to this virus, leading to a major cultivar renewal worldwide. This has caused high variability in chilling requirements on new releases that remain unknown in many cases. In many apricot-growing areas, the lack of winter chilling is becoming a limiting factor in recent years. To deal with this situation, growers must choose cultivars well adapted to their areas. However, the information available on the agroclimatic requirements of the cultivars is very limited. To fill this gap, in this work, we have characterized the chilling requirements of 13 new apricot cultivars from Europe (France, Greece and Spain) and North America (USA) in two experimental collections in Aragón (Spain). We established the chilling period using male meiosis as a biomarker for endodormancy release over two years. Chilling requirements ranged from 51.9 Chill Portions (CP) to 70.9 CP. Knowing the chilling requirements of cultivars will help growers to select suitable cultivars adapted to the chill availability of their region.
... Chilling and forcing accumulation and their relative importance for leaf-out and flowering To elucidate and compare the effects of chilling and forcing conditions on the timing of spring phenology, we calculated species-specific chilling and forcing accumulations for FLD and FFD at each site, respectively. We chose the Dynamic model 95 to quantify chilling accumulation, because it is widely regarded as the most robust chilling model due to its rigorous theoretical structure and ability to explain phenological variation. 32 As forcing model, we used the Growing Degree Hour (GDH) model, 96 which can estimate forcing accumulation at hourly intervals. ...
Leaf-out and flowering in any given species have evolved to occur in a predetermined sequence, with the inter-stage time interval optimized to maximize plant fitness. Although warming-induced advances of both leaf-out and flowering are well documented, it remains unclear whether shifts in these phenological phases differ in magnitudes and whether changes have occurred in the length of the inter-stage intervals. Here, we present an extensive synthesis of warming effects on flower-leaf time intervals, using long-term (1963-2014) and in situ data consisting of 11,858 leaf-out and flowering records for 183 species across China. We found that the timing of both spring phenological events was generally advanced, indicating a dominant impact of forcing conditions compared with chilling. Stable time intervals between leaf-out and flowering prevailed for most of the time series despite increasing temperatures; however, some of the investigated cases featured significant changes in the time intervals. The latter could be explained by differences in the temperature sensitivity (ST) between leaf and flower phenology. Greater ST for flowering than for leaf-out caused flowering times to advance faster than leaf emergence. This shortened the inter-stage intervals in leaf-first species and lengthened them in flower-first species. Variation in the time intervals between leaf-out and flowering events may have far-reaching ecological and evolutionary consequences, with implications for species fitness, intra/inter-species interactions, and ecosystem structure, function, and stability.
... Chilling accumulation models have been proposed for growers over the last sixty years. Three of the most widely used models are the Utah Chilling Unit Model (Richardson et al. 1974), the Chilling Hours Model (Weinberger 1950), and the Dynamic Model (Fishman et al. 1987). Chilling Hours (CH) are widely accepted as industrial standards for chilling measurement among perennial and annual crops (Covert 2011). ...
Determination of chilling and heat requirements is respected in the selection of the suitable cultivars for producers to avoid damages caused by an inadequate winter chilling in a certain area. It also play an important role within a breeding program, when selecting parents to get late or early flowering cultivars. The present study aimed to estimate the chilling and heat requirements of breaking bud dormancy for flowering and vegetative growth in three Iranian almond cultivars in an orchard located in the suburbs of Garmdarreh (32.45°N; 50.91°E; altitude 1960 m). The three almond cultivars had different flowering times, i.e. early: ʻMohebʼ, medium: ʻMamaieʼ and late: ʻRabiʼ. To provide adequate chilling, fourteen-year-old trees were exposed to low temperature treatments (4 ± 1 °C) to simulate 0–1500 h of chilling at 250 h intervals. The cultivars varied in their chilling and heat requirements in terms of chilling hours and growing degree hours, GDH, to achieve bud break for flowering, i.e. ‘Moheb’ (250 h and 2132 GDH), ‘Mamaie’ (500 h and 2460 GDH) and ‘Rabi’ (500 h and 2624 GDH). To achieve bud break for leaf growth, the late-leafing cultivar (‘Rabi’) required 750 chilling hours and a heat requirement of 3608 GDH. The earlier-leafing cultivars (‘Moheb’ and ‘Mamaie’) had lower heat requirements for leaf unfolding. Although ‘Rabi’ and ‘Mamaie’ had similar chilling requirements of 500 h, ‘Rabi’ required almost a week (168 h) of warm weather after chilling to achieve bud break. This implies that spring frost is rarely a problem for ‘Rabi’ in Iran. ‘Moheb’ was not suitable because of its low chilling and heat requirements, hence its inability to escape early spring frosts and late winter cold.
... In dormancy research, a well-known example of such poor model choice is the widespread preference for the straightforward but inaccurate Chilling Hours model over the more complex Dynamic model (Luedeling, 2020). Whereas the Chilling Hours model can easily be implemented in a spreadsheet, the Dynamic model is less intuitive and it requires relatively complex calculations (Fishman et al., 1987b). This complexity has been a major deterrent to the use of this model among researchers, farmers and practitioners. ...
... Under favourable chilling temperatures, x is mostly synthesized and accumulated. This process is fitted by four parameters in the PhenoFlex framework: A 0 , A 1 , E 0 and E 1 (Equation 1) (Fishman et al., 1987a(Fishman et al., , 1987bLuedeling et al., 2021). ...
Olives are one of the most economically relevant crops in the Mediterranean area but this region is experiencing a strong warming due to climate change. Therefore, it would be of great interest to estimate the possible implications of climate change on olive flowering timing by modelling its thermal requirements, and aerobiological records have proved to be a useful tool for monitoring regional olive phenology. Recently, a new phenological modelling framework has been developed called PhenoFlex. It has shown excellent results in estimating the thermal requirements of fruit trees. However, this framework has not previously been applied to olive trees or tested using aerobiological data, which could present greater spatial distribution than in situ phenological observations. This study has a threefold aim: i) to detect the trends in the main pollen season start date of Olea during the past 25 years in a western Mediterranean region (Alentejo, Portugal); ii) to evaluate the applicability of the PhenoFlex modelling framework to olive aerobiological data, and iii) to use the modelled parameter estimates to evaluate the influence of projected future climate change scenarios on Olea flowering regional onset dates. Our results showed that global warming had not produced any significant trend in the olive flowering onset dates until the present time, and they are not expected to do so in the near future, either. A temperature increase during winter was observed that is delaying the fulfilment of the Olea chilling requirements, but this is compensated for by a reduction in the forcing period due to higher temperatures observed during spring. However, our study points out a significant increase in the interannual variability of flowering onset dates, which could compromise fruit development and adversely affect the yield, raising uncertainty in olive fruit production in the near future.
... (Bayazit et al., 2012).The chilling requirement for true dormancy is genetically determined and varies depending on the fruit species and variety (Fadón et al., 2020). Some of the commonly used methods for determining the chilling requirement of plants can be listed as follows: Classical method (Weinberger, 1950), Utah method (Chill Unit) (Richardson et al., 1974), Dynamic method (Fishman et al., 1987). While the ratios between winter cold forecasts calculated by different models vary widely around the world (Luedeling and Brown 2011), they also vary widely between years and regions in growing regions (Luedeling et al. 2009f). ...
Dormancy is a mechanism developed by temperate climate trees to sustain vital activities during low winter temperatures. In autumn, as the days shorten and decrease in temperature, plants shed their lea ves and enter dormancy by minimizing their growth. During winter dormancy, plant metabolism comes to a virtual standstill, due in part to low temperatures that slow chemical activity. Plants exposed to low temperatures meet their dormancy needs throughout the winter. The dormancy can vary depending on ecological conditions, cultural practices, as well as the species and variety of the fruit. In regions where winters are warm, failure to meet the chilling requirement of fruit types and varieties can lead to irregularities, abnormal flower bud formation, and high rates of flower bud drop, resulting in inefficiency and fluctuations in yield. The dormancy mechanism in fruit trees can vary depending on the minimum and maximum temperatures that occur during the winter season. Even if environmental conditions are suitable, flower and leaf buds cannot develop during the period when winter begins, and they remain dormant. In order to the buds to come out of real rest, they need to be exposed to cold for a certain period of time. This event is called "chilling" and the time required to reach this amount is called "chilling time". In this review, it is aimed to determine the differences between the Classic, Utah and Dynamic models used in the calculation of chilling hours and to determine the suitability of these models for different fruit species and varieties.
... R Core Team, 2021) within R Studio (RStudio Team, 2021). Chill accumulation was calculated from hourly temperature data for each winter based on the dynamic model (chill portions; Fishman et al., 1987aFishman et al., , 1987b using the chillR package (Luedeling, 2020). Three inputs were then used for model development, daily maximum (T max ) and minimum temperatures (T min ), and chill accumulation (chill, which is a function of temperature). ...
... The Dynamic Model [16,17] performed better than the other models in quantifying the chilling requirements of several cultivars in a study carried out in Lleida (Spain) and Naoussa (Greece) [13]. This model postulates that winter chill accumulates in a two-step process. ...
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.
... La période de floraison est la durée en jours qui sépare le début et la fin de la floraison. (Fishman et al., 1987a(Fishman et al., , 1987b) et quantifié en tant que portion de froid (PC). Ce modèle s'est révélé le plus approprié en régions chaudes telle que la Tunisie (Elloumi et al., 2013;Ghrab et al., 2014;Benmoussa et al., 2017). ...
La Tunisie a été identifiée comme un 'Hotspot' pour des hausses de températures observées et projetées. Ces changements climatiques ont eu des incidences importantes sur l'agriculture dont le secteur oléicole qui a des retombés socio-économiques importants à échelle nationale et régionale. Dans ce cadre, la phénologie florale connait depuis quelques années un regain d'intérêt, afin d'estimer la future adaptation de l'olivier (Olea europaea L.) dans des différentes zones de production. L'objectif de ce travail est d'évaluer l'adaptabilité phénologique de quatre variétés d'olivier locales (Chemlali Sfax, Chétoui) et étrangères (Arbequina, Koronéiki) à divers conditions agro-climatiques du centre et du sud tunisien : Jammel (35°75', 10°75'), Sfax (34°94', 10°60') et Zarziz (33°30', 11°06'). Le débourrement, les stades préfloraison et la floraison ont été suivis dès le début de la saison de l'année 2015 et ont été liés, par la suite, aux conditions climatiques de chaque zone. Les résultats obtenus ont montré que la phénologie florale de l'olivier est variable en fonction du génotype et des conditions climatiques de chaque environnement. Le débourrement des bourgeons floraux a été plus précoce dans la région de Zarzis caractérisée par un hiver chaud avec une moyenne d'accumulation de froid de 28.4 CP et 'Chemlali' était la plus précoce (entre 17 et 21 Mars) par rapport aux autres variétés. Les stades préfloraison et la période de la floraison sont principalement liés aux températures printanières et à l'altitude de la zone de production. Suite à des hausses de températures printanières (températures maximales > à 35°C) des impacts néfastes sur la phénologie florale (brunissement et blocage de développement des boutons floraux en stade différenciation) ont été observés dans la région de Jammel sur la variété Chetoui. Ces impactes ont été moins importants pour les autres variétés et dans les deux autres régions vues que l'élévation de la température a eu lieu vers fin de la période de leur floraison. En conclusion, ce travail préliminaire met l'accent sur les avantages des essais multi-environnements pour la sélection des meilleurs génotypes d'olivier adaptés aux 32 conditions locales et comme outil pour faire face à la variabilité future annoncée des conditions environnementales causée par le réchauffement climatique. Abstract Tunisia has been identified as a 'Hotspot' for observed and projected temperature increases. These climate changes have significant impacts on agriculture, including the olive sector that has significant socioeconomic benefits at the national and regional levels. In this context, floral phenology has experienced renewed interest in recent years, in order to estimate the future olive tree (Olea europaea L.) adaptation in different production areas. The objective of this study is to evaluate the phenological adaptability of four local (Chemlali Sfax, Chétoui) and foreign (Arbequina, Koronéiki) olive cultivars to various agro-climatic conditions in central and southern Tunisia: Jammel (35 ° 75 ', 10 ° 75'), Sfax (34 ° 94 ', 10 ° 60') and Zarziz (33 ° 30 ', 11 ° 06'). Budburst, pre-flowering and flowering stages were monitored from the start of the 2015-season and were, subsequently, linked to the climatic conditions of each area. Results showed that the olive floral phenology is variable depending on the genotype and the climatic conditions of each environment. Budburst stage was earlier in the Zarzis region characterized by a warm winter with an average chill accumulation of 28.4 CP and 'Chemlali' was the earliest (between 17 and 21 March) compared to the other cultivars. Pre-flowering and flowering stages are mainly related to spring temperatures and the production area altitude. Following spring temperatures increases (maximum temperatures > 35 ° C), harmful impacts on floral phenology (browning and development block of flower buds in the differentiation stage) were observed on the 'Chetoui' cultivar in the Jammel region. These impacts were less important for the other cultivars and in the two other regions where the temperature increase took place towards the end of their flowering period. In conclusion, this preliminary study emphasizes the advantages of multi-environment trials for the selection of the best olive genotypes adapted to local conditions and as a tool to deal with the predicted future variability of environmental conditions caused by global warming.
... The information was obtained from the same meteorological stations. Daily chill accumulation (in Chill Portions) was calculated according to the Dynamic Model [29] using hourly temperature data, and heat accumulation (in Growing Degree Hours-GDH) was calculated according to Anderson et al. [30], using a base temperature of 4 • C and an optimum temperature of 26 • C [31]. The chill and heat phases were delimited, taking into account the relationship between budbreak dates and the means of 10 days of daily chill and heat units from 1 November (of the preceding year of recorded budbreak) to 30 April, using a Partial Least Squares (PLS) regression. ...
Grapevines are among the crops that could suffer stronger effects under climate change, although the effect can differ based on cultivars and location. The aim of this work was to analyse the phenological response of the Verdejo variety compared to other two white varieties (Viura and Sauvignon Blanc) cultivated in Rueda Designation of Origin (DO), Spain, under the present climate conditions, and their potential shifts under projected climate change scenarios. Phenological dates referring to budbreak, flowering, véraison and harvest were analyzed for the period 2008–2021 in 13 plots, together with the weather conditions at daily time scale recorded during the same period. The chill and heat units were evaluated to determine the starting date for heat accumulation, as well as the base temperature to reach each phenological stage. The influence of temperature (maximum and minimum) and water availability averaged for different periods between phenological events were evaluated, and the information was used to project potential changes in phenology by 2050 and 2070 under two Representative Concentration Pathway (RCP) scenarios: RCP4.5 and RCP8.5. An advance of all phenological dates was projected, in particular for véraison and ripening. Verdejo could suffer slightly higher advance than Sauvignon Blanc, and, in any case, ripening will happen under warmer conditions. By 2050, flowering could be advanced between seven and nine days, depending on the emission scenario. However, véraison could be advanced about 13 or 14 days under the RCP4.5 scenario and between 16 and 19 days under the RCP8.5 scenario. Ripening could be reached by 2050 up to 20 days and 25 days earlier, respectively, under the RCP4.5 and the RCP8.5 emission scenarios, and up to 29 days earlier by 2070. These projections may imply further impacts on grapes and wines for the aforementioned cultivars associated to harvest under warmer conditions.
... To summarize winter chill accumulation, we considered the winter season between 1st November (the starting day for chill accumulation in the northern hemisphere) and 28th February (Campoy et al., 2012) in each year and at each site. Winter chill accumulation were quantified in Chill Portions (CPs) by the Dynamic model (Fishman et al., 1987a(Fishman et al., , 1987bErez et al., 1990) and Chill Hours (CHs) by the 0-7.2 C model (Weinberger, 1950), which is proved to be the most accurate and the most widely used model, respectively . ...
Given the strong sensitivity of sweet cherry trees to air temperature and the foreseeable warming under future climates, it becomes urgent to analyse spatiotemporal variability of growing conditions in main production areas of China. Here, we estimated changes of three climate metrics, that is, winter chill, heat accumulation and the risk of spring frost events, by using 22 global climate models over the historical and future (represented by central years 2050s and 2085s) time stages. Statistically downscaled daily maximum and minimum temperatures at 14 sites under representative concentration pathway (RCP) 4.5 and 8.5 scenarios were used. The results show a general increase of available winter chill for most sites in Bohai and Lanzhou–Lianyungang Railway line agro‐climatic zones, and the increase in chill accumulation could reach up to 15.2% in these regions for RCP4.5 by 2085 s. However, the most dramatic winter chill decrease is projected to occur in the southwest region under the RCP8.5 scenario by 2085 s. Additionally, the increase rate of heat accumulation during the forcing period shows spatially consistency, and the most pronounced increase is found in the RCP8.5 by 2085 s. In the north region, median heat accumulation increases by 17.5%–21.0% in the 2050 s under RCP4.5. Similar increasing range could be found in the southwest station. High frost risk areas are found in the southwestern region for both baseline and future climate scenarios. Across the 14 study sites, Mengzi and Kunming have the highest meteorologically defined risk of spring damaging frost with accumulated 335 growing degree days (GDDs) and 264 GDDs before the last spring frost event, respectively. Overall, this study provides projected characteristics of site‐specific growing conditions for sweet cherry trees in main production regions. The results could be useful for decision‐making such as selection of appropriate species and varieties in adapting to future warming.
Fundamental questions in bud dormancy remain, including what temperatures fulfill dormancy requirements (i.e., chill accumulation). Recent studies demonstrate freezing temperatures promote chill accumulation and cold hardiness influences time to budbreak – the phenotype used for dormancy evaluations. Here we evaluated bud cold hardiness ( CH ) and budbreak responses of grapevines ( Vitis hybrids) throughout chill accumulation under three treatments: constant (5°C), fluctuating (−3.5 to 6.5 °C daily), and field conditions (Madison, WI, USA). Chill treatments experiencing lower temperatures promoted greater gains in cold hardiness ( CH field > CH fluctuating > CH constant ). All treatments decreased observed time to budbreak with increased chill accumulation. However, perceived treatment effectiveness changed when time to budbreak was adjusted to remove cold acclimation effects. Among three classic chill models (North Carolina, Utah, and Dynamic), none were able to correctly describe adjusted time to budbreak responses to chill accumulation. Thus, a new model is proposed that expands the range of chill accumulation temperatures to include freezing temperatures and enhances chill accumulation under fluctuating temperature conditions. Most importantly, our analysis demonstrates adjustments for uneven acclimation change the perceived effectiveness of chill treatments. Therefore, future work in bud dormancy would benefit from simultaneously evaluating cold hardiness.
Highlight
A new chill accumulation model demonstrates how bud cold hardiness changes elicited by chill treatments affect the interpretation of thermal effectiveness in promoting dormancy progression and release.
Olive trees, alongside grapevines, dominate the Mediterranean tree crop landscape. However, as climate change intensifies, the Mediterranean region, which encompasses 95% of the global olive cultivation area, faces significant challenges. Rising carbon dioxide (CO 2) levels, increasing temperatures, and declining precipitation pose substantial threats to olive tree performance. Photosynthesis, respiration, phenology, water use and ultimately yield are possibly the main factors affected. To address this future scenario, it is crucial to develop adaptation and mitigation strategies. Nevertheless, breeding programs and field management practice testing for tree crops are time-consuming endeavors. Fortunately, models can accelerate the evaluation of tailored solutions. In this review, we critically examine the current state of olive tree modeling and highlight key areas requiring improvement. Given the expected impact of climate change, prioritizing research on phenology, particularly regarding bloom and pollination, is essential. Simulations of biomass should incorporate approaches that account for the interactive effects of CO 2 and temperature on photosynthesis and respiration. Furthermore, accurately simulating the influence of water stress on yield necessitates the development of models that integrate canopy behavior with root performance under conditions of water scarcity. By addressing these critical aspects, olive tree models can enhance our understanding of climate change impacts and inform sustainable agricultural practices.
Sixty-seven apple tree accessions from the Centre for the Conservation of Agricultural Biodiversity of Tenerife (CCBAT) were molecularly characterised for the first time with 13 simple sequence repeats (SSRs). Additionally, previously studied genotypes from the Canary Islands (Tenerife, La Palma and Gran Canaria), Galicia, Asturias and commercial reference varieties were studied to identify possible synonymies and genetic structures, in order to improve the conservation of this genus in the germplasm bank. Thirty-three different genotypes were found in the new accessions analysed (51% clonality): sixteen of them (48%) exclusive to Tenerife, with no genetic coincidence with previous studies, making a total of thirty-three genotypes unique to Tenerife and sixty-five in the whole of the Canary Islands. The analysis of the population structure grouped the apple genotypes into two reconstructed panmictic populations (RPPs), one formed by local varieties or traditional ones ('Peros'), RPP1, from all the regions studied, and the other formed by local and commercial varieties, RPP2. The RPP1 genotypes identified in Tenerife seem to show better adaptation to low chill, with a positive and significant correlation (0.388, p < 0.01), highlighting the importance of local varieties and the need for their conservation. This is the first study reporting significant correlation between genetic structure and chilling requirements.
Timing of flowering and leaf budbreak in hazelnut is determined by chilling and growing degree day requirements. Hazelnuts are self-incompatible, making it important to choose pollinizer cultivars that will shed pollen at the time that production cultivars are receptive. Since time of flowering can be highly variable depending on the local climate, quantifying chilling and growing degree day requirements can be useful for determining the suitability of a cultivar to a particular region. This is especially important when considering new growing regions for a crop, as well as for matching time of pollen shed of new pollinizers with female receptivity in production cultivars. In this study, hazelnut stems were forced in the greenhouse at regular intervals to determine earliest onset of flowering and leaf budbreak under controlled conditions. These data, along with field phenological observations, were then used to determine chilling and growing degree day requirements. The genotypes studied included ‘Raritan’, ‘Monmouth’, ‘Somerset’, and ‘Hunterdon’ from Rutgers University; ‘OSU 541.147’ The Beast™ from the Hybrid Hazelnut Consortium; and five additional C. avellana selections. Two years of chilling and growing degree day requirements are presented. The results showed that chilling requirements of catkins are lower than those of female flowers in most genotypes, with vegetative buds requiring the largest amount of chilling. Interestingly, we found considerable variation among genotypes in this study, with some requiring more than twice as much chilling as others. In contrast to chilling requirements, growing degree day requirements more consistent among genotypes.
The Trás-os-Montes agrarian region (TM; north-eastern Portugal) is a traditionally growing area of almond trees. However, climate change may significantly alter the current growing conditions and threaten sustainability. Chilling and forcing conditions in TM are assessed herein, also considering different varietal phenological timings. The dynamic model/chill portions (CP) and chilling hour (CH) models are used to assess the chilling phase. For the forcing phase, growing degree hours (GDH) and growing degree days (GDD) models are selected, hinting at differences between simpler (CH and GDD) and more complex models (CP and GDH). Furthermore, the climate change projections for these models are assessed. The models are computed using daily temperatures for baseline (Iberia01, 1971–2015) and two future periods (EURO-CORDEX: medium-term, 2041–2060, and long-term, 2061–2080), following two anthropogenic forcing scenarios (RCP4.5 and RCP8.5). For the future, a five-member ensemble of regional-global climate model chains is used. Projections for CP and CH show decreases, mostly for RCP8.5, whereas projections for GDH and GDD reveal an increase in heat conditions until the beginning of summer. GDH shows that potentially damaging high temperatures during summer, effectively lead to a decrease in heat accumulation for almond trees. CP and GDH, more biologically effective, seem to be more accurate in capturing climate change impacts. For the three varietal groups, the late cultivar may experience a greater reduction of CP and GDH compared to early and mid-season varieties. Nonetheless, the increase in heat forcing should be more detrimental than the decrease in chilling conditions. Although almond production may be compromised in the future, adequate adaptation options are suggested to mitigate future losses of yield/quality and warrant its sustainability.
Rising global temperatures are affecting plant phenology. Spring warming can lead to early flowering due to accelerated heat accumulation after dormancy. Winter warming, however, may counteract this acceleration by extending the chilling period required for endodormancy release. We tested this hypothesis with historical bloom data of a flowering cherry (Prunus x yedoensis) collected from multiple locations in Japan across a latitudinal gradient. We determined differential chilling and forcing temperature effects based on advances (-) or delays (+) of bloom dates per degree Celsius of change (temperature sensitivity, S T). We applied a chilling-forcing modeling approach to reveal and disentangle the differential temperature effects during and after dormancy on spring phenology across different latitudes over time. Our analysis showed that the effects of chilling temperatures during dormancy were variable along the latitudinal gradient, while the effect of forcing temperatures after dormancy was more consistent regardless of latitude. Notably, the elevated temperatures, and thereby reduced chilling, during endodormancy delayed the bloom dates at lower latitudes, and this trend was more pronounced in recent years. Our results support the hypothesis that the effect of winter warming during endodormancy can offset or even outweigh the effect of spring warming by extending the dormancy period, and this can manifest as an overall delay in bloom dates. While the delay in flowering phenology due to winter warming is observable only in lower latitudes currently, it is likely to expand to higher latitudes in the future climate if the warming trend continues. Our findings also highlight the value of concerted long-term phenological records that can provide insights into the mechanisms underlying plasticity in tree physiology with a unique opportunity to predict their responses in a changing climate.
Impact of climate change affects chilling and heat accumulation that phenological development of plant needs, air temperature being determinant for flowering, pollination and fruit production, but few knowledges are available in the winter and spring climate of Tétouan. The physiological mechanisms of the reproductive cycle that controls pollen emission are related with temperature, and different environmental factors regulate strongly the reproductive phases of the plant’s life cycle. However, from an empirical point of view, the alternance between endodormancy and ecodormancy is not well detectable. Our work focuses on determining the heat accumulation periods associated with the thermal balance needed to fulfill the chilling and heat required for budbreak and bloom timing. To evaluate Morus, Pistacia, Quercus and Olea response to changes in chill and heat accumulation rates, the Dynamic Model and the Growing Degree-Days Method were used. Regression analyses identified the chilling and forcing periods for these taxa. Over the past 12 years, chill accumulation during tree dormancy increased significantly for most of woody taxa studied, while heat accumulation decreased not significantly for all taxa. Heat accumulation was the main driver of bloom timing, with effects of variation in chill accumulation.
Temperate trees require low temperatures during winter and subsequent warm conditions in early spring to flower and eventually bear fruit. Many parts of the Mediterranean region feature winters with low and sometimes marginal chill accumulation. To assess historic and future agroclimatic conditions for cultivating temperate trees (including almonds, pistachios, apricots, sweet cherries and apples), we mapped winter chill throughout this important growing region. We used on-site weather records (1974–2020) to calibrate a weather generator and produced data for historic and future scenarios. To broaden our analysis, we spatially interpolated chill for the whole Mediterranean basin. We supplemented our simulation outcomes by collecting expert knowledge (from farmers and researchers) regarding observed climate change impacts on temperate orchards as well as future risks and concerns generated by climate change. Results showed that northern African growing regions have experienced major chill losses, a likely cause of the irregular and delayed bloom highlighted by experts. The same regions, together with southern Europe, may lose up to 30 Chill Portions by 2050 under a moderate warming scenario. For the future, experts foresee increasing risk of spring frost in early-blooming cultivars, exacerbated bloom-related problems and increasing occurrence of heat waves. Our results provide evidence of likely climate change impacts on temperate orchards. Expert knowledge proved instrumental in interpreting the simulation results as well as in orienting climate change adaptation strategies. The results we present are useful for farmers and orchard managers planning new plantings, as well as for researchers and policy makers developing strategies to adapt fruit orchards to the impacts of climate change.
Climate change is expected to pose major challenges for olive cultivation in many Mediter-ranean countries. Predicting the development phases of olive trees is important for agro-nomic management purposes to foresee future climate impact and proactively act toward adaptation and mitigation strategies. In this study, a statistical model was developed based on winter chill accumulation and, in sequence, on heat accumulation to assess the changes in flowering occurrence for Olea europaea cv. Koroneiki, in the island of Crete, Greece. The model was based on and calibrated with long-term phenological observations and temperature data from four different sites in the island, spanning an elevation gradient between 45 and 624 m a.s.l. This model was used to assess the changes in flowering emergence under two Representative Concentration Pathway scenarios, RCP4.5 and RCP8.5, as projected by seven high-resolution Euro-CORDEX Regional Climate Models. Changes in chill accumulation were determined using the Dynamic Model. Reduction rates in chill accumulation for the whole chilling season ranged between 12.0 and 28.3% for the near future (2021-2060) and 22.7 and 70.9% for the far future (2061-2100), in comparison to the reference period of 1979-2019. Flowering was estimated to occur between 6 and 10 days earlier in the near future and between 12 and 26 days earlier in the far future, depending on the elevation and the climate change scenario.
Rooted ‘Redhaven’ peach [ Prunus persica (L.) Batsch] cuttings were exposed to diurnal temperature cycles. A severe reduction in lateral vegetative bud break was found in plants refrigerated at 4°C and given 8 hr daily exposure to 19° (±0.1°). Nearly complete chilling negation occurred in plants exposed to diurnal cycles including 8 hr of 20° or 21°. Also, effect decreased with increased time (0 to 8 hr per day) of exposure to 24°. Buds on plants exposed to cycles including 20° for 2 and 4 hr showed no chilling negation, but gradual increases in chilling negation occurred with longer exposures to 20°. ‘Harvester’ peach plants were exposed to 2, 7, or 12 days of 23° following the accumulation of one-fourth, one-half, or three-fourths of the chilling requirement. Chilling negation occurred only with the 12-day exposure to 23° when high temperatures were applied following the accumulation of one-fourth and one-half of the chilling requirement. No chilling negation was found after 12 days’ exposure to 23° if three-fourths of the chilling requirement had accumulated before exposure.
Floral bud break of 1-year-old rooted cuttings of ‘Sungold’ nectarine ( Prunus persica (L.) Batsch) was observed following chilling at constant and diurnal temperature regimes. Continuous exposure to 10°C was as effective as 7°. Rate of bud break increased as chilling increased up to 750 hours. Floral bud break of plants exposed to 14 days at 30° during the middle of the chilling period was more rapid but failed to reach the level of activity of plants exposed to constant temperatures. A chill unit model developed for ‘Sungold’ nectarine which has a chilling requirement of 550 hours indicated a broader range of effective temperatures and a higher optimum for rest completion as compared to the Utah model and predicted rest completion more accurately than other methods when applied to orchard temperature data.
Leaf bud break of ‘Redhaven’ and ‘Redskin’ peach ( Prunus persica (L.) Batsch) following exposure of plants to temperature cycles of 1, 3, 6 and 9 days was examined. During each cycle the plants were exposed to 4°–6°C for 2/3 of the cycle length and 24° for the remaining 1/3 with all cycles repeated until the plants were exposed to a designated number of chilling hours. Thus, all plants within each treatment were exposed equally (in total) to chilling and heat. No lateral bud (LB) break occurred with ‘Redskin’ in the 1-day cycle, a low level was obtained in the 3-day cycle and good bud break occurred in the continuous chilling control and the 6 and 9 day cycles. With ‘Redhaven’ no LB break was evident in the 1 day cycle while the 3, 6, and 9 day cycles responded similar to the continuous chilling control. From these data it was concluded that chilling (4°-6°) accumulated during the 20 to 40 hrs prior to the onset of high temperature was susceptible to high temperature negation.
With controlled temperatures low temperature efficiency in releasing peach buds from dormancy follows an optimum curve in which 6°C is the optimum for average lateral leaf buds and 10°C is about half as efficient. “Weighted chilling hours” instead of “chilling hours” was proposed as a chilling measurement criterion. A high temp of 21°C, when alternated daily with low temp, nullified the low temp effect; a high of 18°C had no effect. Interrupting the chilling by 2 separate periods of 11 and 12 days at 20°C did not show any nullifying effect, but greatly enhanced lateral leaf bud break.
A mathematical model relating environmental temperatures to rest completion of 2 peach cultivars has been developed. The model equates temperatures to effective chill-units, such that, one can predict when rest will or has been completed with a high degree of accuracy.
A chill unit model was developed for ‘Starkrimson Delicious’ ( Malus domestica Borkh.) apples grown under the wide range of temperature and elevations in North Carolina. The model relates air temperature to effective chill units and predicts rest completion for North Carolina-grown apples more accurately than previously reported models. The model proposes a broader range of effective temperatures and incorporates a greater negative effect when temperatures exceed 21°C for rest. According to the model, 1200 chill units are required to break rest of apple buds. Growing degree hours correlated with each apple bud developmental stage, as well as from projected date of rest completion to full bloom, were determined using various base temperatures.
The effect of exposure of small peach plants ( Prunus persica (L.) Batsch cvs. Redhaven and Redskin) to daily fluctuating temperatures (16 hours low: 8 hours high) of 6-15°, 6-18°, 6-21° and 6-24°C was examined in comparison with continuous chilling at 4° and a non-chilled control. Even though all chilling treatments received the same amount of chilling (weighted chilling hours), good leaf bud break was obtained only in the continuous 4°, 6-15° and 6-18° treatments. No lateral leaf buds opened in the 6-21°, 6-24° or the non-chilJed controls of both cultivars. The 6-15° temperature regime was more efficient than continuous chilling in breaking bud rest on a weighted chilling hour basis. ‘Redskin’ lateral buds were shown to have a higher chilling requirement than ‘Redhaven’. Terminal buds especially of ‘Redhaven’ showed a very low chilling requirement. Treating plants with 50 or 150 mg/liter GA 3 slightly advanced bud break but did not affect the level of sprouting.
The reversibility of vernalisation in Petkus winter rye has been studied in detail, by using alternating periods, during germination, of low and high temperature of varying durations. The degree of devernalisation by exposure to subsequent high temperature varies with the initial duration of vernalisation and becomes progressively less as vernalisation proceeds. A quantitative method of studying these effects is described, and a revised schema of the dynamic aspects of vernalisation put forward.
A COMMON method of comparing rates of reactions or processes in
biological systems is the use of the temperature coefficient, or
Q10, the ratio of the rates of a reaction or process at
(T+10)° C and T° C. James1 says of the
Q10: ``As it is readily calculated, easily understood, and
carries no theoretical implications, it remains a useful and favourite
method of recording the temperature relations of complex biological
processes''. But because Q10 values of different processes
tend to fall within certain limits, they are often used to indicate
types of reactions that might be occurring.
The effect of cycle length on chilling negation by high temperatures in dormant peach leaf buds Quantitative chilling enhancement and negation in peach buds by high temperatures in a daily cycle Rest prediction model for low-chilling 'Sungold' nectarine
- A Erez
- S Lavee
- A Erez
- G A Couvlllon
- C H Hendershotr
- P R G1lreath
- D W Buchanan
EREZ, A. & LAVEE, S (1971). The effect of climatic conditions on dormancy development of peach buds. 1. Temperature. Proc. Am. Soc. Hort. Sci. 96, 711. EREZ, A., COUVlLLON, G. A. & HENDERSHOTr, C. H. (1979a). The effect of cycle length on chilling negation by high temperatures in dormant peach leaf buds. J. Am. Soc. Hort. Sci. 104, 573. EREZ, A., COUVILLON, G. A. & HENDERSHOTT, C. H. (1979b). Quantitative chilling enhancement and negation in peach buds by high temperatures in a daily cycle. J. Am. Soc. Hort. Sci. 104, 536. G1LREATH, P. R. & BUCHANAN, D. W. (1981). Rest prediction model for low-chilling 'Sungold' nectarine. J. Am. Soc. Hort. Sci. 106, 426. HEGARTY, T. W. (1973). Temperature coefficient (Qlo), seed germination and other biological processes.
Characterization of the moderate temperature effect on peach bud rest
- Erez