Effect of plant growth regulators and malt extract on somatic embryogenesis and in vitro grafting of Citrus plants

Abstract

Citrus fruits are among the most consumed fruits in the world. This is mainly due to their high content in vitamin C and other health-promoting bioactive compounds. Developing new and efficient propagation systems for Citrus plants is of high importance to rejuvenate old orchards and to satisfy the high demand of consumers. Herein, we aimed to establish an efficient regeneration method through micrografting for Citrus plants. Nucellar embryos of sour orange (Citrus aurantium L.) were taken from mature seeds and cultured on plant growth regulator (PGR)-free Murashige and Skoog medium with some modifications (MSm) to be used as rootstock. For scion preparation, undeveloped ovules of sweet orange Citrus sinensis (L.) Osbeck cv. Washington Navel were cultured either on PGR-free MSm medium, MSm medium supplemented with malt extract at different concentrations, or on MSm medium supplemented with different PGRs to induce somatic embryogenesis. The findings showed that after 10 days of culture, all nucellar embryos of sour orange were developed into seedlings. Besides, it was found that the number and size of embryos vary in each seed. The number of embryos ranged from 1 to 8, with a degree of polyembryony ranging from 3.08 to 4.12. Regarding sweet orange cv. Washington Navel, the highest percentage of embryogenic callus formation (50%) was observed on the medium containing 500 mg/L malt extract, with no significant difference with media containing 1000 and 1500 mg/L malt extract (46%). However, callus and proembryo morphology and proliferation varied depending on malt extract concentration. Surprisingly, none of the media containing PGRs showed embryogenic callus formation. Micrografting was performed by inserting somatic embryos of sweet orange cv. Washington Navel on decapitated sour orange seedlings. The micrografted plants were transferred to MSm medium supplemented with 1 mg/L gibberellic acid where a survival rate of 100% as well as normal growth and development of plants were observed.

Keywords

• citrus
• embryogenèse nucellaire
• embryogenèse somatique
• in vitro
• microgreffage
• régénération