Optimizing In Vitro Growth of Carob (Ceratonia siliqua L.)

Abstract

The carob tree (Ceratonia siliqua L.)  is an important perennial leguminous species with high ecological and economic importance, particularly in arid and semi-arid environments.  This research investigated the effects of plant growth regulators, namely indole-3-acetic acid (IAA) and benzyladenine (BA), applied both individually and in combination, on root development, biomass accumulation, mineral nutrient composition and carbohydrate metabolism of carob seedlings cultivated under in vitro conditions. The results revealed that IAA at a concentration of 1.5 mg/L significantly increased root length and dry root weight, thereby indicating an optimal auxin concentration for root growth. The application of BA at moderate concentration also improved the root/shoot ratio, however higher concentrations of either regulator caused inhibitory effects. The combined application of IAA (1.5 mg/L) and BA (0.5 mg/L) produced the most pronounced positive effects, resulting in balanced root and shoot growth, increased nutrient uptake, and improved carbohydrate distribution. This treatment resulted in a notable increase in the accumulation of soluble sugars and starch within both shoot and root tissues, signifying improved metabolic efficiency. An inverse relationship between sucrose and starch levels was observed, suggesting efficient conversion of sucrose into starch under combined hormone treatment. Overall, these results underscore the importance of a balanced application of auxins and cytokinins in optimizing initial growth, physiological efficacy and in vitro propagation efficiency of Ceratonia siliqua L., providing a reliable strategy for sustainable cultivation and conservation of this valuable species.