Effects of ectomycorrhizal fungal inoculation on growth and rooting of carob tree (Ceratonia siliqua L.)

Abstract

The present work investigated the ability of the ectomycorrhizal (ECM) fungi, Pisolithus tinctorius (Pers.) Coker and Couch to improve the growth and root formation in carob seedlings (Ceratonia siliqua L.). Root initiation of hypocotyl cuttings in vitro was enhanced by treatments with different concentrations of either fungal culture filtrate or indole-3-butyric acid (IBA) or in combination. The ectomycorrhization protocol for carob seedlings comprised of three different treatments: in vivo or in vitro inoculation and non-inoculated seedlings. Results obtained after six months of acclimatization showed that inoculation had a positive effect on the growth and rooting of carob plants. Moreover, plants mycorrhized in vitro or in vivo outperformed non-mycorrhized ones in plant height, number of internodes, number of leaves, leaf length, number of roots, maximal root length, and fresh and dry weights of both stems and roots. Indeed, the optimum response was encountered in the seedlings inoculated in vitro. The application of culture filtrate on hypocotyl cuttings revealed significant differences between experimental treatments for the number and length of roots. The best response was recorded in medium containing fungal culture filtrate with 40%. Root formation of hypocotyl cuttings of carob plants was also enhanced by the use of IBA, where the best rooting was manifested in treatment with IBA at a concentration of 2 mg/l. The application of P. tinctorius culture filtrate to the culture medium of hypocotyl cuttings after pretreatment by immersing in IBA was even more effective in improving root formation than the treatment of hypocotyls base with IBA alone. The present study demonstrated the possibility of developing procedures to improve the rooting growth of carob plants by establishing a successful artificial symbiosis with P. tinctorius. Highlights from this work could play a crucial role in arid ecosystem rehabilitation and controlled mycorrhization programs.