Control of in vitro shoot tip necrosis in Carob Ceratonia siliqua L.

Shoot tip necrosis (STN) is a physiological abnormality whereby the apical shoot initially becomes necrotic and subsequently dies leading to considerable loss of shoots and hampering any commercial application of carob (Ceratonia siliqua L.) micropropagation. The objective of the present study is the optimization of a method to alleviate STN during in vitro multiplication of carob dealing with a range of culture media compounds. Obtained results showed that macroelement strength of the culture medium as well as cytokinin and calcium concentrations were the most important factors in controlling STN incidence in carob. In fact, Zimmerman macroelements are most efficient in terms of STN reduction (only 5% STN observed) and shoot multiplication (28.75 shoots with 26.8 leaves and 4.73 cm length). Moreover, shoots cultured on Zimmerman or Ca enriched ½MS showed higher mineral nutrient contents than those cultured on low Ca media. On the other hand, most shoots recovered from STN have produced roots in presence of 1 mg.L-1 IAA (70%) and 83% survived after transfer to ex vitro conditions. The performance of Zimmerman macroelements is most likely due to its high Ca concentration (7.3 mM) compared to the other media. This is confirmed by the steep reduction of STN intensity obtained on ½MS enriched with Ca.