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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.

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.

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.