Seasonal climatic change affects lychee (Nephelium lychee Cambess) phenology in Madagascar

The phenology of lychee varies as a function of the developmental stage and season, ensuring adequate energy for new shoots of leaves, floral buds and axillary buds at the beginning of spring. Number and sex of flowers are dependent on climatic conditions, with temperature and humidity being the main parameters. Unfavorable climatic conditions during plant development are the source of several problems, because of the variations in climate can damage the intermolecular interactions necessary to adequate growth, which hampers the development of the plants and the placing in fruit. In this study, lychee development was evaluated as a factor of temperature and rain in field cultivation in Madagascar: the aim of this study was to determine the impacts of climate on Lychee chinensis tree development. Plant phenology was studied in the field during different seasons in four lychee production sites in Madagascar, considering the following stages: flowering, fruit formation, fruit development and ripening. The used phenological codes were based on the extended BBCH-scale (Biologische Bundesanstalt, Bundessortenamt und Chemische Industrie) and describe the growth stages of the lychee plant using a three-digit numerical system. The analysis of auxins (IAA) and abscisic acid (ABA) content in different plant parts by high-performance liquid chromatography (HPLC), coupled to a diode array detector (DAD), was performed to evaluate potential different physiological dynamics in leaves from branches with or without flowers. The description according to the BBCH codes showed growth difficulties, which were explained by a reversal of the production phases (stages 5 to 9) toward the resumption of the growth phases (stages 0 to 3). Auxins and abscisic acid, detected by HPLC, could indicate sensitivity of the plants to climatic variability: the results of the ABA analysis showed that the leaves contained about 10 mgABA 100 g-1 dry weight. This proportion is low compared to the quantities of IAA. Based on the BBCH model, research shows that the phenological pattern of lychee follows a more marked evolution by phase reversal at a critical point in time, during which the stop code leads to growth anomalies. This evolution is considered an anomaly and no longer represents the normal rhythm of lychee development according to the BBCH-scale. Unfavorable climatic conditions that could be classified as climatic disturbance and cause hormonal imbalance could be the reason for this, with potential detrimental effects on lychee cultivation.