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In recent years, global warming and unusually warm winters have caused many problems for pistachio production in Iran. The effects of the Dormex® application were studied in a randomized complete block design with three treatments and three replications on the Akbari commercial pistachio cultivar in Kerman province. Treatments included Dormex® 4%, Volk oil 4%, and control, all applied in mid-February. Flowering time, gum secretion, current branch length, and qualitative and quantitative yield characteristics were measured. Results showed that Volk oil and Dormex® spring treatments caused early flowering in the Akbari cultivar. The Dormex® 4% treatment significantly prolonged flowering time (8 days earlier than Volk oil 4%, and 12 days earlier than the control). Based on the results, Volk oil treatment increased gum secretion from buds and perennial shoots compared to the Dormex® treatment and control. The results of yield indices showed that the weight of clusters in the Dormex® 4% treatment was 2.3 times higher than the control and about 21% more than the Volk oil 4% treatment, showing a significant difference with the control. Dormex® and Volk oil treatments increased split nut percentage by 66 % and 88%, respectively, but there was no significant difference between them. Based on the results, the blank nut percentage in the Dormex® 4% treatment significantly increased compared to the control and Volk oil treatment by 33% and 41%, respectively. The length of current season growth in the Dormex® 4% treatment significantly increased by 68% compared to the control. The Volk oil 4% treatment had no significant effect on the length of current season growth compared to the control.

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 cultivarspecific 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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.

Fig orchard expansion requires knowledge of the thermal requirements of genotypes available in different climatic regions. The budburst of fig cultivars was assessed by biological single-node cutting and exposure to artificial chilling. Cuttings from five cultivars were collected during two crop seasons, subsequently packaged in a horizontal position in a cold chamber (8 ± 0.5°C), and artificially chilled for 0, 40, 80, 120, and 160h. Cuttings were preserved under controlled conditions (23 ± 1°C, RH 85%, and 16h photoperiod). The variables evaluated were the budding velocity, average time and final rate of sprouting, vigorous shoot rate, and average time to leaf opening. The single-node cutting test allowed the assessment of dormancy, which is influenced by the accumulation of chilling in each crop season. The average time and final budding rate varied depending on the temperature requirements for budding. The cultivars were classified on an increasing scale according to their chilling requirements as follows: Pingo de Mel < Roxo de Valinhos < Brown Turkey < White Genova < Troyano. The traditional cultivar in Brazil is Roxo de Valinhos, but all of the cultivars studied had the potential to diversify the fig orchards in this region. [ABSTRACT FROM AUTHOR]

Invasive exotic species produce impacts of different magnitudes in the environment. The colonization success of a species depends on several factors. Different research demonstrated that chill hours accumulation is one of the most important factors affecting the germination of the tree species Elaeagnus angustifolia L. This non-native species is considered invasive, even noxious, in different parts of the world, modifying terrestrial and aquatic environments. We investigate the chill hours accumulation effect on the seed germination of E. angustifolia under two soil moisture conditions (field capacity and half-field capacity). We also evaluated the survival of seedlings of the species for 240 days under the two mentioned moisture conditions. With the data obtained, we made two heat maps (one for each moisture condition) with the probability of germination of E. angustifolia in Argentina related to the natural availability of chill hours. We found that as the chill hours accumulation increased, germination of E. angustifolia increased in half-field capacity treatment and decreased in field capacity conditions. Seedling survival was 100% in both water regimes. Heat maps show the break dormancy probability of E.angustifolia seeds throughout the Argentine territory, with high potential of germination in Patagonia. In addition to contributing to the prevention of the invasion of E. angustifolia in Argentina, the information generated in our study can be helpful in other regions of the world since the significant genetic variability that the studied species presents can make its environmental distribution range unpredictable. [ABSTRACT FROM AUTHOR]

The large amount of olive cultivars conserved in germplasm banks can be used to overcome some of the challenges faced by the olive growing industry, including climate warming. One effect of climate warming in olive is the difficulty to fulfill the chilling requirements for flowering due to mild winter temperatures. In the present work, we evaluate seven olive cultivars for their adaptation to high winter temperatures by comparing their flowering phenology in the standard Mediterranean climate of Cordoba, Southern Iberian Peninsula, with the subtropical climate of Tenerife, Canary Islands. Flowering phenology in Tenerife was significantly earlier and longer than in Cordoba. However, genotype seems to have little influence on the effects of the lack of winter chilling temperatures, as in Tenerife. This was found even though the cultivars studied had a high genetic distance between them. In fact, all the cultivars tested in Tenerife flowered during the three-year study but showed asynchronous flowering bud burst. 'Arbequina' showed an earlier day of full flowering compared with the rest of the cultivars. The results observed here could be of interest to refine the phenological simulation models, including the length of the flowering period. More genetic variability should be evaluated in warm winter conditions to look for adaptation to climate warming. [ABSTRACT FROM AUTHOR]

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.

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

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. [ABSTRACT FROM AUTHOR]

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

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

Dormancy release dynamics in olive tree (Olea europaea L.) reproductive buds as affected by cold accumulation, tree bearing status, and budburst temperature was studied under natural and controlled conditions, using both cuttings and container- and field-grown plants. The chilling necessary for dormancy release was acquired at different times within the bud population, presenting a progressive pattern of reproductive budburst. Once sufficient chilling is accumulated, 20 °C is a suitable temperature for reproductive budburst, although higher temperature, e.g., 30 °C, during dormancy release can inhibit budburst. While the bearing status of trees determined the amount of return bloom, dormancy release followed a similar pattern for previously bearing and non-bearing trees. Concurrent with investigating budburst factors, the use of shoot cuttings was tested as a method for olive dormancy release studies by contrasting with results from whole trees. It was found it to be valid for studying reproductive budburst, thus providing a useful method to screen chilling requirements in cultivar evaluation and the breeding programs currently ongoing in this species. However, the method was not valid for vegetative budburst, with varying results between cuttings and the whole plant. [ABSTRACT FROM AUTHOR]

The large amount of olive cultivars conserved in germplasm banks can be used to overcome some of the challenges faced by the olive growing industry, including climate warming. One effect of climate warming in olive is the difficulty to fulfill the chilling requirements for flowering due to mild winter temperatures. In the present work, we evaluate seven olive cultivars for their adaptation to high winter temperatures by comparing their flowering phenology in the standard Mediterranean climate of Cordoba, Southern Iberian Peninsula, with the subtropical climate of Tenerife, Canary Islands. Flowering phenology in Tenerife was significantly earlier and longer than in Cordoba. However, genotype seems to have little influence on the effects of the lack of winter chilling temperatures, as in Tenerife. This was found even though the cultivars studied had a high genetic distance between them. In fact, all the cultivars tested in Tenerife flowered during the three-year study but showed asynchronous flowering bud burst. ‘Arbequina’ showed an earlier day of full flowering compared with the rest of the cultivars. The results observed here could be of interest to refine the phenological simulation models, including the length of the flowering period. More genetic variability should be evaluated in warm winter conditions to look for adaptation to climate warming.

The rate of global warming varies in magnitude between seasons, with warming being more pronounced in winter and spring than in summer and autumn at high latitudes. Winter warming can have profound effects on dormancy release and spring phenology of perennial fruit crops, but potential follow-on impacts on growth, fruit yield or quality have only rarely been investigated. We studied the effects of mild winter warming on spring phenology, current year shoot growth, cropping performance and fruit quality in four field-grown cultivars of blackcurrant with different chilling requirements. Plants were exposed to ambient or slightly elevated (+ 0.5 °C) temperatures from early October to mid-April the following year. Winter warming had few effects on spring phenology and fruit yield, but caused significant changes in berry contents of phenolic compounds and a reduction in soluble sugars. Increased vegetative growth of warmed plants likely accounts for the changes in berry quality. The results demonstrate a persistent effect of winter warming on shoot growth, which indirectly changes fruit quality. [ABSTRACT FROM AUTHOR]

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

Dormancy is an adaptive strategy in plants to survive under unfavorable climatic conditions during winter. In temperate regions, most fruit trees need exposure to a certain period of low temperatures to overcome endodormancy. After endodormancy release, exposure to warm temperatures is needed to flower (ecodormancy). Chilling and heat requirements are genetically determined and, therefore, are specific for each species and cultivar. The lack of sufficient winter chilling can cause failures in flowering and fruiting, thereby compromising yield. Thus, the knowledge of the chilling and heat requirements is essential to optimize cultivar selection for different edaphoclimatic conditions. However, the lack of phenological or biological markers linked to the dormant and forcing periods makes it difficult to establish the end of endodormancy. This has led to indirect estimates that are usually not valid in different agroclimatic conditions. The increasing number of milder winters caused by climatic change and the continuous release of new cultivars emphasize the necessity of a proper biological marker linked to the endo- to ecodormancy transition for an accurate estimation of the agroclimatic requirements (AR) of each cultivar. In this work, male meiosis is evaluated as a biomarker to determine endodormancy release and to estimate both chilling and heat requirements in apricot. For this purpose, pollen development was characterized histochemically in 20 cultivars over 8 years, and the developmental stages were related to dormancy. Results were compared to three approaches that indirectly estimate the breaking of dormancy: an experimental methodology by evaluating bud growth in shoots collected periodically throughout the winter months and transferred to forcing chambers over 3 years, and two statistical approaches that relate seasonal temperatures and blooming dates in a series of 11–20 years by correlation and partial least square regression. The results disclose that male meiosis is a possible biomarker to determine the end of endodormancy and estimate AR in apricot. [ABSTRACT FROM AUTHOR]

Dormancy is an adaptive strategy in plants to survive under unfavorable climatic conditions during winter. In temperate regions, most fruit trees need exposure to a certain period of low temperatures to overcome endodormancy. After endodormancy release, exposure to warm temperatures is needed to flower (ecodormancy). Chilling and heat requirements are genetically determined and, therefore, are specific for each species and cultivar. The lack of sufficient winter chilling can cause failures in flowering and fruiting, thereby compromising yield. Thus, the knowledge of the chilling and heat requirements is essential to optimize cultivar selection for different edaphoclimatic conditions. However, the lack of phenological or biological markers linked to the dormant and forcing periods makes it difficult to establish the end of endodormancy. This has led to indirect estimates that are usually not valid in different agroclimatic conditions. The increasing number of milder winters caused by climatic change and the continuous release of new cultivars emphasize the necessity of a proper biological marker linked to the endo- to ecodormancy transition for an accurate estimation of the agroclimatic requirements (AR) of each cultivar. In this work, male meiosis is evaluated as a biomarker to determine endodormancy release and to estimate both chilling and heat requirements in apricot. For this purpose, pollen development was characterized histochemically in 20 cultivars over 8 years, and the developmental stages were related to dormancy. Results were compared to three approaches that indirectly estimate the breaking of dormancy: an experimental methodology by evaluating bud growth in shoots collected periodically throughout the winter months and transferred to forcing chambers over 3 years, and two statistical approaches that relate seasonal temperatures and blooming dates in a series of 11–20 years by correlation and partial least square regression. The results disclose that male meiosis is a possible biomarker to determine the end of endodormancy and estimate AR in apricot.

Dormancy release dynamics in olive tree (Olea europaea L.) reproductive buds as affected by cold accumulation, tree bearing status, and budburst temperature was studied under natural and controlled conditions, using both cuttings and container- and field-grown plants. The chilling necessary for dormancy release was acquired at different times within the bud population, presenting a progressive pattern of reproductive budburst. Once sufficient chilling is accumulated, 20 °C is a suitable temperature for reproductive budburst, although higher temperature, e.g., 30 °C, during dormancy release can inhibit budburst. While the bearing status of trees determined the amount of return bloom, dormancy release followed a similar pattern for previously bearing and non-bearing trees. Concurrent with investigating budburst factors, the use of shoot cuttings was tested as a method for olive dormancy release studies by contrasting with results from whole trees. It was found it to be valid for studying reproductive budburst, thus providing a useful method to screen chilling requirements in cultivar evaluation and the breeding programs currently ongoing in this species. However, the method was not valid for vegetative budburst, with varying results between cuttings and the whole plant.

Air temperature plays a major role in the growth cycle of fruit trees. Chilling and forcing are two of the main mechanisms that drive temperate fruit development, namely dormancy and active plant development. Given the strong sensitivity of these crops to air temperature and the foreseeable warming under future climates, it becomes imperative to analyze climate change impacts for fruit trees. The fruit sector in Portugal has risen significantly over the last decades, gaining increasing importance both internally and through exports. The present research assesses the impacts of climate change on the chilling and forcing for economically relevant fruit trees in Portugal, namely apples, oranges, pears, and plums. To assess temperate fruit chilling and forcing conditions, the chilling portions (CP) and growing degree-hours (GDH) were computed over Portugal, for the recent-past (1989–2005) and future (2021–2080) periods, following two anthropogenic radiative forcing scenarios (RCP4.5 and RCP8.5). Future climate data were obtained from four regional-global climate model pairs to account for model uncertainties. Bias-correction methodologies were also applied. A spatial analysis over the main regions with PDO “Protected Denomination of Origin” or PDI “Protected Geographical Indication” of origin of each fruit tree was performed. Future projections show a clear decrease in chilling for all regions and fruit types in Portugal. Nonetheless, given the current chilling values in Portugal and the relative importance of chilling accumulation for each fruit type, these changes are more significant for certain varieties of apples than for other types of fruit. Regarding forcing, the future projections highlight an increase in its values throughout the different fruit tree regions in Portugal, which should lead to earlier phenological timings. These changes may bring limitations to some of the most important Portuguese temperate fruit regions. The planning of suitable adaptation measures against these threats is critical to control the risk of exposure to climate change, thus warranting the future sustainability of the Portuguese fruit sector, which is currently of foremost relevance to the national food security and economy.

Air temperature plays a major role in the growth cycle of fruit trees. Chilling and forcing are two of the main mechanisms that drive temperate fruit development, namely dormancy and active plant development. Given the strong sensitivity of these crops to air temperature and the foreseeable warming under future climates, it becomes imperative to analyze climate change impacts for fruit trees. The fruit sector in Portugal has risen significantly over the last decades, gaining increasing importance both internally and through exports. The present research assesses the impacts of climate change on the chilling and forcing for economically relevant fruit trees in Portugal, namely apples, oranges, pears, and plums. To assess temperate fruit chilling and forcing conditions, the chilling portions (CP) and growing degree-hours (GDH) were computed over Portugal, for the recent-past (1989–2005) and future (2021–2080) periods, following two anthropogenic radiative forcing scenarios (RCP4.5 and RCP8.5). Future climate data were obtained from four regional-global climate model pairs to account for model uncertainties. Bias-correction methodologies were also applied. A spatial analysis over the main regions with PDO "Protected Denomination of Origin" or PDI "Protected Geographical Indication" of origin of each fruit tree was performed. Future projections show a clear decrease in chilling for all regions and fruit types in Portugal. Nonetheless, given the current chilling values in Portugal and the relative importance of chilling accumulation for each fruit type, these changes are more significant for certain varieties of apples than for other types of fruit. Regarding forcing, the future projections highlight an increase in its values throughout the different fruit tree regions in Portugal, which should lead to earlier phenological timings. These changes may bring limitations to some of the most important Portuguese temperate fruit regions. The planning of suitable adaptation measures against these threats is critical to control the risk of exposure to climate change, thus warranting the future sustainability of the Portuguese fruit sector, which is currently of foremost relevance to the national food security and economy. [ABSTRACT FROM AUTHOR]

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Blooming in temperate fruit species is triggered by chilling and heat requirements (CR and HR), with a wide range of requirements within the same species. CR for flower bud dormancy release has become a limiting factor for geographical adaptation of fruit trees in warmer regions. The present study investigated the genetic basis of CR and HR to break dormancy and flowering time (FT) in an almond x peach F2 progeny. FT, HR and CR were evaluated over two consecutive years (2015/2016 and 2016/2017). Seven out of the eight identified quantitative trait loci (QTLs) were found in both periods of analysis. They affected eight traits, and included a consistent QTL for breaking dormancy, CR and HR. Two of them, affecting FT and HR for FT (GDHF), colocalized in G1, and the remaining QTLs, affecting chilling and heat requirements, both influenced by dormancy breaking (DB), were located in G6. These results indicate that factors not related to DB affect flowering time in this population. Implications of the results in peach breeding are discussed. [ABSTRACT FROM AUTHOR]

Bloom time in sweet cherry (Prunus avium L.) is a highly heritable trait that varies between genotypes and depends on the environmental conditions. Bud-break occurs after chill and heat requirements of each genotype are fulfilled, and dormancy is released. Bloom time is a critical trait for fruit production as matching cultivar adaptation to the growing area is essential for adequate fruit set. Additionally, low chilling cultivars are of interest to extend sweet cherry production to warmer regions, and for the crop adaptation to increasing winter and spring temperatures. The aim of this work is to investigate the genetic control of this trait by analyzing multiple families derived from the low chilling and extra-early flowering local Spanish cultivar ‘Cristobalina’ and other cultivars with higher chilling requirements and medium to late bloom times. Bloom time evaluation in six related sweet cherry populations confirmed a high heritability of this trait, and skewed distribution toward late flowering, revealing possible dominance of the late bloom alleles. SNP genotyping of the six populations (n = 406) resulted in a consensus map of 1269 SNPs. Quantitative trait loci (QTL) analysis using the Bayesian approach implemented by FlexQTL™ software revealed two major QTLs on linkage groups 1 and 2 (qP-BT1.1m and qP-BT2.1m) that explained 47.6% of the phenotypic variation. The QTL on linkage group 1 was mapped to a 0.26 Mbp region that overlaps with the DORMANCY ASSOCIATED MADS-BOX (DAM) genes. This finding is consistent with peach results that indicate that these genes are major determinants of chilling requirement in Prunus. Haplotype analysis of the linkage group 1 and 2 QTL regions showed that ‘Cristobalina’ was the only cultivar tested that contributed early bloom time alleles for these two QTLs. This work contributes to knowledge of the genetic control of chilling requirement and bloom date and will enable marker-assisted selection for low chilling in sweet cherry breeding programs.

Summary: Globally, spring phenology and abiotic processes are shifting earlier with warming. Differences in the magnitudes of these shifts may decouple the timing of plant resource requirements from resource availability. In riparian forests across the northern hemisphere, warming could decouple seed release from snowmelt peak streamflow, thus reducing moisture and safe sites for dominant tree recruitment.We combined field observations with climate, hydrology, and phenology models to simulate future change in synchrony of seed release and snowmelt peaks in the South Platte River Basin, Colorado, for three Salicaceae species that dominate western USA riparian forests.Chilling requirements for overcoming winter endodormancy were strongest in Salix exigua, moderately supported for Populus deltoides, and indiscernible in Salix amygdaloides. Ensemble mean projected warming of 3.5°C shifted snowmelt peaks 10–19 d earlier relative to S. exigua and P. deltoides seed release, because decreased winter chilling combined with increased spring forcing limited change in their phenology. By contrast, warming shifted both snowmelt peaks and S. amygdaloides seed release 21 d earlier, maintaining their synchrony.Decoupling of snowmelt from seed release for Salicaceae with strong chilling requirements is likely to reduce resources critical for recruitment of these foundational riparian forests, although the magnitude of future decoupling remains uncertain. [ABSTRACT FROM AUTHOR]

Bloom time in sweet cherry (Prunus avium L.) is a highly heritable trait that varies between genotypes and depends on the environmental conditions. Bud-break occurs after chill and heat requirements of each genotype are fulfilled, and dormancy is released. Bloom time is a critical trait for fruit production as matching cultivar adaptation to the growing area is essential for adequate fruit set. Additionally, low chilling cultivars are of interest to extend sweet cherry production to warmer regions, and for the crop adaptation to increasing winter and spring temperatures. The aim of this work is to investigate the genetic control of this trait by analyzing multiple families derived from the low chilling and extra-early flowering local Spanish cultivar 'Cristobalina' and other cultivars with higher chilling requirements and medium to late bloom times. Bloom time evaluation in six related sweet cherry populations confirmed a high heritability of this trait, and skewed distribution toward late flowering, revealing possible dominance of the late bloom alleles. SNP genotyping of the six populations (n = 406) resulted in a consensus map of 1269 SNPs. Quantitative trait loci (QTL) analysis using the Bayesian approach implemented by FlexQTL™ software revealed two major QTLs on linkage groups 1 and 2 (qP-BT1.1m and qP-BT2.1m) that explained 47.6% of the phenotypic variation. The QTL on linkage group 1 was mapped to a 0.26 Mbp region that overlaps with the DORMANCY ASSOCIATED MADS-BOX (DAM) genes. This finding is consistent with peach results that indicate that these genes are major determinants of chilling requirement in Prunus. Haplotype analysis of the linkage group 1 and 2 QTL regions showed that 'Cristobalina' was the only cultivar tested that contributed early bloom time alleles for these two QTLs. This work contributes to knowledge of the genetic control of chilling requirement and bloom date and will enable marker-assisted selection for low chilling in sweet cherry breeding programs. [ABSTRACT FROM AUTHOR]

The chilling requirements for dormancy release and heat requirements for flowering were studied for three successive years in eleven Prunus salicina L. cultivars that spanned the range of flowering times in this species. Different methods for estimating chilling requirements were evaluated and compared, and correlations between chilling requirements, heat requirements and flowering date were established. The cultivars examined showed a range of chilling requirements (chill units, CU), spanning from 334.3 CU (‘Pioneer’) to 987.5 CU (‘Songold’). The heat requirements for flowering ranged between 5990 and 9228 growing degree hours. The chilling requirements were significantly different among cultivars, whereas no cultivar effect was found for the heat requirement values. In addition, chill portions were the variable that correlated the most with flowering date in Japanese plum. The dissection of flowering date into chilling and heat requirements indicates that chilling requirements is the main variable driving the variation of flowering time within Japanese plum cultivars. [ABSTRACT FROM AUTHOR]

Temperate deciduous trees can only be productive where winters are cold enough to meet their chilling needs. In the Mediterranean region, chill has traditionally been sufficient for many species, but this may change as temperatures increase. We explored the region’s present and future suitability for temperate trees by quantifying chill for the Sfax region in central Tunisia, one of the warmest regions where temperate nuts are commercially grown. We assessed climatic risk by calculating historic chill (since 1973) and using a weather generator calibrated with local weather data (1973-2015) to produce 101 years of chill estimates (computed with the Dynamic Model) and 3 past and 72 future scenarios (for 2041-2070 and 2071-2100, using two representative concentration pathways: RCP4.5 and RCP8.5). For almonds and pistachios, we compared available chill during the chilling period with the species’ estimated chilling requirements, and we computed the date by which sufficient chill was expected to have accumulated. Our findings indicated severe chill losses for all future scenarios. For all species, the current chill period is no longer expected to be sufficient for meeting chilling requirements in the future. Chill needs may still be fulfilled later in the year, especially for low-chill almonds, but this would result in delayed phenology, with possible adverse effects on productivity. Temperate nut production is thus unlikely to remain viable at this site, highlighting an urgent need to identify locally appropriate adaptation options. This challenge is likely shared by other warm production regions of temperate fruits and nuts around the world. [ABSTRACT FROM AUTHOR]

Key message: Comparison of five sweet cherry cultivars—over 3 years—shows an asynchronous early and late flower development, but a consistent, specific flower developmental stage for dormancy.Abstract: In temperate woody deciduous perennials, dormancy is a survival strategy to persist winter temperatures; but chilling is also required for the release of flower bud dormancy and for the completion of flower development. This was noticed over 100 years ago, but the biological mechanisms underlying cold regulated dormancy and its release remain poorly understood. That chilling is required for the completion of flower development led us to hypothesize that a particular stage of flower development may be consistently associated with the dormant phase of flower bud development. Flower development of five sweet cherry cultivars was examined weekly under stereoscopic and optical microscopes over 3 years. Chilling requirements for each cultivar were determined by placing weekly shoots in forcing conditions. The establishment of a flower developmental scale showed that early and late flower development, in the autumn and spring, were asynchronous among cultivars and years. However, in all circumstances, dormancy occurred at the same stage of flower development, characterized by the presence of all flower whorls, with the anthers clearly differentiated in the four locules, and the pistil showing an incipient ovary, style and stigma. The length of time flower buds remained at this stage differed between cultivars and was related to their chilling requirements and date of flowering. The observation that a particular stage of flower development, common to the five cultivars examined, exists during the combined rest period provides a framework for further studies on the physiology and cellular biology of dormancy. [ABSTRACT FROM AUTHOR]

Temperate woody perennials enter into a dormant status during winter in order to survive low temperatures. However, dormancy is not just a survival strategy, since cold winter temperatures are required for proper flowering. Global warming is having an impact on the phenology of woody perennials; warmer temperatures during dormancy may lead to an erratic reproductive behaviour due to the lack of chilling accumulated during winter. Although the relevance of dormancy for the adaptation of temperate woody perennials is well known, the biological processes behind dormancy remain unclear. In this work, we review how shoot and seedling experiments have contributed to the current knowledge on dormancy in woody perennials from the early discovery of the role of cold temperatures for adequate flowering to the latest knowledge on dormancy physiology and genetics. The information available has been organised in seven sections: (i) Climate change and winter dormancy in woody perennials; (ii) Discovering the importance of cold and the establishment of dormancy bases; (iii) Experiments to estimate the dormancy period; (iv) Exploring the physiology of dormancy; (v) Looking for biological markers for the dormancy status through histochemical techniques; (vi) Molecular biology of bud dormancy and (vii) Conclusions and perspectives. [ABSTRACT FROM AUTHOR]

Olive (Olea europaea L.) is a crop well adapted to the environmental conditions prevailing in the Mediterranean Basin. Nevertheless, the increasing international demand for olive oil and table olives in the last two decades has led to expansion of olive cultivation in some countries of the southern hemisphere, notably in Argentina, Chile, Perú and Australia. While the percentage of world production represented by these countries is still low, many of the new production regions do not have typical Mediterranean climates, and some are located at subtropical latitudes where there is relatively little information about crop function. Thus, the primary objective of this review was to assess recently published scientific literature on olive cultivation in these new crop environments. The review focuses on three main aspects: (a) chilling requirements for flowering, (b) water requirements and irrigation management, and (c) environmental effects on fruit oil concentration and quality. In many arid and semiarid regions of South America, temperatures are high and rainfall is low in the winter and early spring months compared to conditions in much of the Mediterranean Basin. High temperatures have often been found to have detrimental effects on olive flowering in many olive cultivars that have been introduced to South America, and a better understanding of chilling requirements is needed. Lack of rainfall in the winter and spring also has resulted in an urgent need to evaluate water requirements from the flower differentiation period in the winter to early fruit bearing. Additionally, in some olive growing areas of South America and Australia, high early season temperatures affect the timing of phenological events such that the onset of oil synthesis occurs sooner than in the Mediterranean Basin with most oil accumulation taking place in the summer when temperatures are very high. Increasing mean daily temperatures have been demonstrated to decrease fruit oil concentration (%) and negatively affect some aspects of oil quality based on both correlative field studies and manipulative experiments. From a practical standpoint, current findings could be used as approximate tools to determine whether the temperature conditions in a proposed new growing region are appropriate for achieving sustainable oil productivity and quality.

Based on observations for the beginning of the flowering stage of Malus domestica (apple) and Pyrus communis (pear) for the 1950–2018 period, phenological trends in north-eastern Belgium were investigated in function of temperatures during dormancy. Moreover, two different phenological models were adapted and evaluated. Median flowering dates of apple were on average 9.5 days earlier following warm dormancy periods, and 11.5 days for pear, but the relationship between bloom date and temperature was found not to be linear, suggesting delayed fulfilment of dormancy requirements due to increased temperatures during the chilling period. After warm chilling periods, an average delay of 5.0 and 10.6 days in the occurrence date of dormancy break was predicted by the phenological models while the PLSR reveals mixed signals regarding the beginning of flowering. Our results suggest overlapping chilling and forcing processes in a transition phase. Regarding the beginning of flowering, a dynamic chill model coupled to a growing degree days estimation yielded significantly lower prediction errors (on average 5.0 days) than a continuous chill-forcing model (6.0 days), at 99% confidence level. Model performance was sensitive to the applied parametrization method and limitations for the application of both models outside the past temperature ranges became apparent.

Seedless barberry ( Berberis vulgaris L. var. asperma) is a particular fruit crop that has been used extensively as a medicinal plant in traditional medicine. For the first time, chilling and heat requirements of seedless barberry for breaking of dormancy were calculated. The studied genotypes assayed were selected from Khorasan-e-Jonoobi province in the eastern part of Iran. Uniform one-year-old cuttings were obtained from the shrubs of each genotype after leaf fall and were stored at 4 ± 1 °C for 0.00 (control), 400, 700, 1100 and 1400 h. Six characters including days to the first leaf bud break, days to the first flower bud break, days to full flower bud break, leaf bud number, flower bud number and flowered bunch number were examined. In addition, chilling and heat requirements were determined. Results showed that chilling treatments had significant effects on all the measured traits. The cuttings reached a period of chilling of 1100–1400 h showed the earliest full flower bud break. The highest number of flowered bunches was observed in the cuttings treated with 1400 h chilling. All the genotypes had a chilling requirement of 1400 h. On the contrary, the genotypes were classified into two groups based on heat requirements with 2904 and 3432 growing degree hours (GDHs), however, they were not significantly differed in this regards. In conclusion, the present information can be used to advise seedless barberry farmers about which genotypes are best suited to areas with different winter conditions. [ABSTRACT FROM AUTHOR]

The chilling requirements of 35 kiwifruit genotypes in south China were evaluated. The number of hours at low temperature (0–7.2°C) required to break natural dormancy was determined. Results showed that the average chilling requirement of the 35 genotypes was 675 h. The chilling requirement of 89% of the genotypes ranged from 576 to 768 h. Overall, the chilling requirements of genotypes ofActinidia chinensisvar.deliciosawere higher than those ofActinidia eriantha, which in turn were higher than those ofA. chinensisvar.chinensis. These results provide a basis for breeding and selection of kiwifruit cultivars suitable for cultivation in low-chill areas of south China. [ABSTRACT FROM AUTHOR]

Olive (Olea europaea L.) is a crop well adapted to the environmental conditions prevailing in theMediterranean Basin. Nevertheless, the increasing international demand for olive oil and table olives in the last two decades has led to expansion of olive cultivation in some countries of the southern hemisphere, notably in Argentina, Chile, Perú and Australia. While the percentage of world production represented by these countries is still low, many of the new production regions do not have typical Mediterranean climates, and some are located at subtropical latitudes where there is relatively little information about crop function. Thus, the primary objective of this review was to assess recently published scientific literature on olive cultivation in these new crop environments. The reviewfocuses on three main aspects: (a) chilling requirements for flowering, (b) water requirements and irrigation management, and (c) environmental effects on fruit oil concentration and quality. In many arid and semiarid regions of South America, temperatures are high and rainfall is low in the winter and early spring months compared to conditions in much of the Mediterranean Basin. High temperatures have often been found to have detrimental effects on olive flowering in many olive cultivars that have been introduced to South America, and a better understanding of chilling requirements is needed. Lack of rainfall in the winter and spring also has resulted in an urgent need to evaluate water requirements from the flower differentiation period in the winter to early fruit bearing. Additionally, in some olive growing areas of South America and Australia, high early season temperatures affect the timing of phenological events such that the onset of oil synthesis occurs sooner than in the Mediterranean Basin with most oil accumulation taking place in the summer when temperatures are very high. Increasingmean daily temperatures have been demonstrated to decrease fruit oil concentration (%) and negatively affect some aspects of oil quality based on both correlative field studies and manipulative experiments. From a practical standpoint, current findings could be used as approximate tools to determine whether the temperature conditions in a proposed new growing region are appropriate for achieving sustainable oil productivity and quality. [ABSTRACT FROM AUTHOR]

Blooming time is an essential trait in almond cultivars, mainly because of the occurrence of frosts during bloom and early fruit development, when the flowers and the young fruits are very sensitive to freezing temperatures. Traditional almond growing has been mostly restricted to coastal regions where the risk of frosts was minimal or nil, but at present it is shifting to two very different environments: inland regions with high frost incidence and subtropical regions with very low chilling accumulation. Therefore, the chilling and heat requirements for almond blooming have acquired the highest interest when describing a new cultivar and, as a consequence, these requirements have been analysed in this review, as well as the genetics of blooming time as a basis for defining late bloom as an objective in breeding programmes or not. Additionally, the breeding efforts directed to obtain later blooming cultivars have been reviewed, stating that no breeding has been yet undertaken towards earlier bloom because many traditional cultivars were early blooming. Almond breeding has been highly effective in obtaining very late blooming cultivars, well adapted to growing regions with high frost risks, but these very late blooming releases may conversely show adaptation problems in low chilling regions. [ABSTRACT FROM AUTHOR]

Chilling requirements of temperate fruit species may vary substantially depending on the climatic conditions where they grow. In addition, in a climate change context, a precise knowledge of these requirements and their effect on productivity is critical for choosing the best suited cultivars to assure long-term adaptation under low-chill environments. To date most studies circumvented the analysis of productivity when assessing chilling requirements in different climatic conditions. Thus, the chilling and heat requirements of different sweet cherry cultivars ( Prunus avium L.) for breaking dormancy, flowering and fruit set were investigated in two contrasted growing areas in Tunisia: Ain-Drahem (800 m above sea level) and Tibar (328 m above sea level). Additionally, we evaluated several parameters to assess the productivity under these two different conditions. Low chill cultivars showed a higher fruit set in both locations suggesting a better adaption to warm-winter conditions. This three-year study establishes the basis of sweet cherry adaptation under two contrasted locations in Northern Africa. [ABSTRACT FROM AUTHOR]

For fruit tree (Prunus) species, flower bud dormancy completion determines the quality of bud break and the flowering time. In the present climate change and global warming context, the relationship between dormancy and flowering processes is a fundamental goal in molecular biology of these species. In almond [P. dulcis (Miller) Webb], flowering time is a trait of great interest in the development of new cultivars adapted to different climatic areas. Late flowering is related to a long dormancy period due to high chilling requirements of the cultivar. It is considered a quantitative and highly heritable character but a dominant gene (Late bloom, Lb) was also described. A major QTL (quantitative trait loci) in the linkage group (LG) 4 was associated with Lb, together with other three QTLs in LG1 and LG7. In addition, DAM (Dormancy-Associated MADS-Box) genes located in LG1 have been largely described as a gene family involved in bud dormancy in different Prunus species including peach [P. persica (L.) Batsch] and Japanese apricot (P. mume Sieb. et Zucc.). In this work, a DAM transcript was cloned and its expression was analysed by qPCR (quantitative Polymerase Chain Reaction) in almond flower buds during the dormancy release. For this purpose two almond cultivars (‘Desmayo Largueta’ and ‘Penta’) with different chilling requirements and flowering time were used, and the study was performed along two years. The complete coding sequence, designated PdDAM6 (Prunus dulcis DAM6), was subjected to a phylogenetic analysis with homologous sequences from other Prunus species. Finally, expression dynamics analysed by using qPCR showed a continuous decrease in transcript levels for both cultivars and years during the period analysed. Monitoring almond flower bud dormancy through DAM expression should be used to improve almond production in different climate conditions.

Durante el reposo invernal los frutales de clima templado deben estar expuestos a bajas temperaturas para satisfacer sus necesidades de frío. La disponibilidad de frío varía entre regiones y entre años, y puede ser insuficiente para los cerezos. Por lo tanto cuando se desea incorporar el cultivo del cerezo a nuevas regiones se debe conocer previamente la disponibilidad de frío invernal. Los objetivos del presente estudio fueron: desarrollar un pronóstico para estimar la disponibilidad de frío invernal y calcular la probabilidad de satisfacer una determinada demanda de frío del año en curso. Los modelos mostraron que el porcentaje de variabilidad explicado de las unidades de frío Utah modificado en las fechas de referencias (UFUM FR) varía entre 50 y 87% para Junín y entre 50 y 86% para San Martín. La probabilidad que posee Junín de alcanzar el valor medio de 884 unidades de frío Utah Modificado (UFUM) es 28%, mientras el valor medio de San Martín es 816 UFUM y su probabilidad es 16%. El pronóstico de frío invernal permitirá al productor evaluar los riesgos que posee su plantación de experimentar daños por falta de frío invernal y eventualmente ejecutar medidas correctivas.During the winter rest, fruit trees of temperate zones should be exposed to low temperatures in order to satisfy their chilling requirements. Chill availability varies through regions and years, and this may be insufficient for cherry trees. Therefore, when farmers want to incorporate new areas, they should be acquainted with winter chilling availability beforehand. The objectives of this study were: to develop a prognosis to estimate the amount of winter chilling and to calculate the probability of satisfying the amount of chilling requirement of any given year. Models showed that the proportion explained by modified Utah chill units at reference date (MUCU RD) varied between 50 to 87% for Junín and 50 to 86% for San Martín. For Junín, the probability to reach an average value of 884 chill units Utah modified (MUCU) is 28%, whereas the average value for San Martín is 816 MUCU and its probability correspond to 16%. The winter chill prognosis will allow the producer evaluates the risks which has its plantation suffer damage due to lack of winter chill and eventually implement corrective measures.

• PLS regression failed to delineate temperature response phases for multi-location dataset. • Estimated agroclimatic requirements differed between study locations. • Site-specific estimates of agroclimatic requirements indicate need for model revisions. • Phenology response to temperature (and thus to global warming) is location-specific. 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. [ABSTRACT FROM AUTHOR]

Most commercial apple cultivars have high to medium chilling requirements and consequently are not grown in regions with warm winters. Furthermore, global climate changes raise the concern that some regions where apples are currently being produced will become unsuitable in the future. Therefore, mapping and understanding the factors governing chilling requirements are important goals towards the breeding of new apple varieties. In this study, we characterized 73 apple accessions: old local accessions, modern cultivars, and selected hybrids, all grown in the Newe Ya’ar germplasm collection in Israel under moderate winter conditions. We measured the time of vegetative bud-break as an indicator of chilling requirements and genotyped the accessions for known genetic markers and for markers we developed by re-sequencing the genome of ‘Anna’, a cultivar with very low chilling requirements. Our results show that while most of the accessions that were characterized as having early bud-break are genetically different from each other, they all share a unique haplotype in a region of ∼190 kb, within a previously identified QTL for bud-break time, on chromosome 9. The alleles in the early bud-break-associated haplotype were not found in any of the late accessions tested, suggesting that the causative difference leading to the variation in bud-break time lays within or near this region, and that there is a common ancestor carrying early bud-break trait of the early accessions tested. Moreover, the markers of the unique haplotype can serve as genetic markers to accelerate the breeding of apple cultivars better adapted to warm climates. [ABSTRACT FROM AUTHOR]