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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.

UMR BFP - Equipe A3C; International audience; 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.

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., This project was supported in part by funding from the Spanish Ministry of Economy and Competitiveness (MINECO/FEDER projects AGL2015-68329-R and RTA2015-00050–00-00, Severo Ochoa Program for Centres of Excellence in R&D 201–2019 SEV-2015–0533) and from the CERCA Programme-Generalitat de Catalunya.

International audience; Determining the flowering and the dormancy phases in fruit trees is a crucial process because of their substantial role in some agricultural practices and crop managements. However, few of these studies were conducted on almond flowering and dormancy, particularly in mild climate areas. This study aimed to simulate the dormancy phases, closely involved in the determination of flowering time of almond species in response to temperature variations. To reach this objective, Partial Least Squares analysis was used. In this regard, climatic and flowering data were collected from Ain Taoudjate in Morocco during the period from 1974 to 2014. In fact, a significant temperature increase was highlighted, inducing a decrease in amounts of chill during the studied period. Using Partial Least Squares analysis, a good fit of data was obtained, particularly using mean and maximal temperatures. Two relevant periods controlling the flowering process were highlighted in Tuono cultivar, in concordance with the sequential model in prediction of flowering times. The first long chilling period started from October 01st to January 11th. During this period, temperatures correlated positively with flowering dates, inducing consequently a delayed flowering dates because of low and slow accumulation of chilling requirements. However, the second short forcing period extended from January 18th to March 09th, during which flowering dates were negatively correlated with temperatures. In fact, the accumulation of certain threshold of Growing Degree Hours and Chill Portions during the two periods respectively could delay flowering, particularly in the context of chilling privation in the coming future, causing a serious problem for fruit trees. Significantly, temperatures during the chilling period seemed to affect effectively the flowering dates of almond than temperatures during the forcing period. In this investigation, we demonstrated that Partial Least Squares showed a good fit in explanation of the flowering process and can be used for prediction of dormancy phases and flowering process.

Chilling and heat requirements for breaking dormancy and flowering were studied in 63 nectarine and118 peach genotypes (Prunus persica (L.) Batsch) for seven years. We compared two methods for estima-tion of requirements and four models for calculation of chill accumulation: Chilling Hours (CH), ChillingUnits (CU), Positive Chilling Units (PCU) and Dynamic, while heat accumulations were estimated in grow-ing degree hours (GDH). Additionally, correlations between chilling requirements, heat requirements andflowering date were established. Our results suggest that the Luedeling model is better than the Alonsomodel to estimate chilling and heat requirements in our field conditions. Moreover, it is recommend-able to calculate the chill accumulation in accordance with the Chilling Hours or Positive Utah models.Additionally, since chilling requirements were positively correlated with flowering dates, they seem tobe important to regulate blooming in nectarine and peach genotypes. Fil: Maulión, Evangelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Centro de Estudios Fotosintéticos y Bioquímicos (i); Argentina Fil: Valentini, Gabriel Hugo. Instituto Nacional de Tecnologia Agropecuaria. Centro Reg.buenos Aires Norte. Estacion Exptal.agrop.san Pedro; Argentina Fil: Kovalevski, Leandro. Universidad Nacional de Rosario. Facultad de Cs.economicas y Estadistica. Escuela de Estadistica; Argentina Fil: Prunello, Marcos. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas; Argentina Fil: Monti, Laura Lucía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Centro de Estudios Fotosintéticos y Bioquímicos (i); Argentina Fil: Daorden, María Elena. Instituto Nacional de Tecnologia Agropecuaria. Centro Reg.buenos Aires Norte. Estacion Exptal.agrop.san Pedro; Argentina Fil: Quaglino, Marta. Universidad Nacional de Rosario. Facultad de Cs.economicas y Estadistica. Escuela de Estadistica; Argentina Fil: Cervigni, Gerardo Domingo Lucio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Centro de Estudios Fotosintéticos y Bioquímicos (i); Argentina

The purpose of this work was to study the response of two apple cultivars bred for low chilling environments to artificial chilling accumulation. Two trials were carried out; in experiment one, excised shoots were randomly taken from "Caricia" and "Princesa", and in experiment two, intact and excised shoots of "caricia", "Princesa" and "Gala" (control) were collected. After collection, both shoot types were exposed to artificial chilling accumulation (4.0 ± 0.5 °C) from 0 to 1200 chill units (CU). Bud break of mixed buds of "Caricia" and "Princesa" was higher than 50% between 0 CU to 1200 CU, irrespective of shoot type. Bud break of "Gala" mixed buds exceeded 50% only in intact shoots after accumulating 900 CU. The mean time to bud break of "Caricia" and "Princesa" diminished with increasing chilling accumulation and stabilized after ~600 CU, depending on the type of shoot and the year of experimentation. The low-chill apple cultivars tested in this work showed shallow dormancy, but they required moderate cold accumulation (800-1150 CU) to fully satisfy their chilling requirements. Thus, although their shallow dormancy makes them suitable for cultivation in chill-deficient environments, they cannot be considered low-chill cultivars. O objetivo deste trabalho foi avaliar a resposta ao acúmulo de refrigeração artificial de dois cultivares de maça de baixo requerimento de frio. Coletaram-se ramos a campo das cultivares “Caricia” e “Princesa”, e da cultivar “Gala” (utilizada como controle), com e sem gemas apicais (ramos intactos e decapitados, respectivamente), as quais foram expostas ao acúmulo de refrigeração artificial (4.0 ± 0.5°C) de zero a 1200 unidades de frio (UF). A brotação das gemas em ambos os tipos de ramos foi maior do que 50% em todo o intervalo de acumulação de frio avaliado em “Caricia” e “Princesa”. No entanto, em “Gala·” a brotação excedeu 50% somente nos ramos intactos depois de acumular 900 UF. Observou-se que o tempo médio para a brotação das gemas de “Caricia” e “Princesa” estabilizou-se acima das 600 UF, dependendo do tipo de ramo e do ano de experimentação. As gemas dos cultivares avaliados neste trabalho mostraram uma dormência pouco profunda, no entanto precisaram de acumulação moderada de frio (800 – 1150 UF) para satisfazer seus requerimentos ecofisiológicos. Portanto, apesar da dormência pouco profunda permitir que estes cultivares sejam adequadamente cultivados em zonas com invernos amenos, não podem ser considerados de baixo requerimento de frio. Fil: Castro, Damian Cesar. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina Fil: Alvarez, Norma Hortensia. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina Fil: Gabriel, Paola. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias; Argentina Fil: Buyatti, Marcela Alejandra. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias; Argentina Fil: Favaro, Juan Carlos. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias; Argentina Fil: Gariglio, Norberto Francisco. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias; Argentina

UMR 1332 - Equipe A3C; 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.

International audience; The efficiency of different temperature cycles in inducing budburst of one-year-old shoots of the apricot cultivar ‘Palsteyn’ from dormancy was evaluated. Three replications of shoots were collected during two consecutive years from adult trees, following the accumulation of different amounts of chilling in the field. Thereafter, shoots were exposed to different temperature cycles in growth chambers, for 60 days. The temperature treatments included a continuous temperature of 5 °C; daily temperature cycles of 19/5 h at 5/15 °C, at 5/20 °C, and at 5/25 °C; and the same temperature cycles for the remainder of the 60-day period, after pretreatment at 5 °C for 30 or 45 days. After the temperature treatments, shoots were forced at 25 °C until budburst. The mean time to budburst (MTB) (in days) of lateral vegetative, terminal vegetative and reproductive buds was evaluated. The efficiency of the different treatments was greatly influenced by the date on which shoots were cut. High temperatures had a more positive effect on the reduction of MTB when chilling accumulation had occurred in the field instead of the growth chamber. After partial chilling accumulation in the field, high temperatures (25 °C) combined with low temperatures are more efficient than cycles of moderate temperatures (15 or 20 °C) to induce an earlier budburst. In view of these results, a parallel accumulation of both chilling and heat requirements after partial chilling accumulation is suggested. The application of these results could assist in the development of more accurate models for the prediction of the overcoming of dormancy and blooming.

10 pages, 4 figures, 4 tables., Chilling requirements for breaking of dormancy and heat requirements for flowering were studied for 3 successive years in 10 apricot cultivars which 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), between 596 CU (Currot) and 1266 CU (Orange Red), though most of them showed chilling requirements between 800 and 1200 CU. The results obtained in different years by the Utah and Dynamic models were more homogeneous with respect to the hours below 7 °C model. The heat requirements for flowering ranged between 4078 and 5879 growing degree hours (GDH). The apricot cultivars showed important differences concerning flowering date, and the results indicate a high positive correlation between chilling requirements and flowering date, as well as a negative correlation between chilling requirements for breaking of dormancy and heat requirements for flowering., The authors are grateful to the Spanish Comisión Interministerial de Ciencia y Tecnología (CICYT) Project AGL2001-1122-CO2-01 for financial support. D.R. is the holder of a grant from the Consejo Superior de Investigaciones Científicas (reference I3PBPD 2001-1).

International audience; A marked increase in air temperature has been observed in France since the end of the 1980s for fruit trees and vine regardless of cropping areas. As phenology is mainly influenced by temperature, changes in vegetative and flowering phenology timing will have agronomic consequences on these perennial productions. It is thus necessary to characterize the present and future trends of bud phenology in the context of global warming. Firstly, long-term series of phenological data extracted from a national data base devoted to fruit trees and vine (called PhénoClim®) have revealed changes in the time-course variations in flowering and vegetative phenology. Surprisingly, quite similar trends toward advances of flowering dates in various fruit trees and bud break dates in vine have been observed in different French cropping areas. In apple and pear trees, a statistical study of phenological series using multiple change-point models clearly support the idea of an abrupt change in the mean dates of flowering stages since the end of the 1980s, the most likely period for this discontinuity being between 1988 and 1989. Similar results were obtained considering phenological series of bud break dates in vine. The concomitancy with the global warming recorded in France since the end of 1980s leads to conclude that these advances in bud phenology could be actual impacts of this warming. Secondly, regarding the analysis of the phenological evolution in terms of temperature effects, modelling works based on the same conception of successive chilling and heat effects were developed to analyze the past and future impacts on bud phenology. For apple tree, a user-oriented software (called Pollenoscope) was exploited to understand the recent advance of mean flowering dates. The results suggest that two opposite trends simultaneously occurred in France since the end of the 1980s: a slower rate of completion of chilling requirements and a higher rate of completion of heat requirements. Nevertheless, the observed advance of mean flowering dates could result of more pronounced increases of temperatures from January to April, corresponding to the period of heat requirements completion for buds in France. In vine, a new model (called Brin) was developed introducing a chilling sub-model contrary to many traditional vine models. The optimal parameters were defined using the PhénoClim® database and the software STICS. The prediction of bud break date was improved by the model Brin. Moreover, a simulation over a future period (2070-2099) was realized using the Brin phenological model and the Arpege climatic model on the basis of A2 and B2 scenarios of IPCC. An increase of the mean advance of bud break could be observed for vine in France, although the dormancy break by chilling would have a marked tendency to be later, as previously suggested for apple tree in a recent past.

8 pages, 4 tables.-- Available Online 17 Sep. 2003., Seed dormancy affects germination and subsequent seedling growth in many plant species. In this work the effect of temperature (cold and heat treatments), flowering time of genotypes, and hardness of endocarp on the break of seed dormancy in four almond cultivars, including a broad range of flowering dates, was studied. Mature seeds, with and without endocarp, were stratified at 7 °C for 1–10 weeks, followed by 5 weeks at 22 °C. The number of germinated seeds were recorded weekly for each cultivar, and cold and heat treatments. Despite the great variability observed within cultivars, a relationship between chilling requirements of cultivars for flowering and stratification requirements of seeds for germination was observed. With endocarp, stratification time required to overcome seed dormancy ranged between 6 (early flowering cultivars Desmayo Largueta and Ramillete) and 8 weeks (late-flowering cultivars Mono and Wawona) on average. Elimination of the endocarp reduced the period of stratification needed for germination in hard-shelled cultivars by 3 weeks. This effect was less important in soft-shelled almonds. No important differences between cultivars were observed for heat requirements. Two weeks at 22 °C was enough to reach the higher germination percentage after each cold treatment., This work has been financed with the project “Mejora Genética del Almendro” (AGL2001-1054-C03-01) from the “Plan Nacional de I+D” of Spanish Ministry of Science and Technology.