Somatic embryogenesis in Malaysian cultivars of sweet potato (Ipomoea batatas L.).

Abstract

Three Malaysian sweet potato cultivars, namely Ipomoea batatas (L.) cv. Gendut, Jalomas and Telong, were investigated for their abilities to produce somatic embryos. Shoot meristems were used as the starting materials and cultured on Murashige and Skoog basal media (Murashige and Skoog, 1962) in the presence of auxin 2,4-dichlorophenoxyacetic acid (2,4-D) or 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). Auxin 2,4,5-T at 5 µM was most effective for the initiation of primary embryogenic formations in Ipomoea batatas (L.) cv. Gendut. However, the cultivar Jalomas embryogenic cells failed to germinate and Telong meristem cultures formed non-embryogenic calli. Ipomoea batatas (L.) cv. Gendut embryogenic cultures consisted of compact and organized cell growths. Ipomoea batatas (L.) cv. Jalomas embryogenic tissues had ruptured cells which subsequently prevented the formation of viable somatic embryos. Ipomoea batatas (L.) cv. Telong consisted of unorganized cell formations, as there was scattered mitotic activity. Subsequently, Gendut cultures were used for the development of secondary embryogenic inductions using pre-embryogenic calli as explants. Pre-embryogenic calli explants treated with hydrogen peroxide and auxin (0.5 µM hydrogen peroxide and 5 µM auxin 2,4,5-T) promoted both non-embryogenic and pre-embryogenic calli productions, while heat pre-treatments (20 minutes of exposure to 500C pre-treatment) promoted embryogenic calli productions and UV-C radiation (1 minute UV radiation pre-treatment) was effective for germinating high number of somatic embryos. Investigations on the antioxidative enzymes that regulated endogenous reactive oxidative species (ROS) in the various morphological structures revealed that the accumulation of hydroxyl and superoxide radicals were important for the initiation of pre-embryogenic formations, while the subsequent accumulation of hydrogen peroxide caused the progression to embryogenic calli formations. Subsequent maturation and germination of these embryogenic calli correlated with reduced ROS, with the increase in superoxide dismutase (SOD) and peroxidase (POD) enzyme activities. The primary induction from meristem explants is important for the production of virus-free planting materials, as viral infections among sweet potato crops are spreading in Malaysia. Secondary embryogenic calli productions provide available embryogenic materials for genetic transfer technologies, artificial seed productions, and the establishment of a germplasm collection.