Evaluation of protocols for regeneration of sweet potato (Ipomoea batatas (l.) Lam.) in tissue culture

Abstract

Tissue culture techniques have opened a new frontier in agricultural science for addressing food security and poverty issues. These techniques have involved development of suitable plant regeneration protocols that can reduce disease infestation by producing healthy plants rapidly and hence increase yields in Kenya. The current research focus in sweet potato (Ipomoea batatas (L.) Lam) has been the development of transgenic sweet potatoes, with ability to resist viral diseases of which suitable plant regeneration protocols are fundamental. A study was conducted at Kenya Agricultural Research Institute (K.A.R.I.) Njoro, to determine an efficient tissue culture protocol for rapid regeneration and multiplication of locally adapted sweet potato cultivars and thereafter compare growth and yield between the regenerated and conventionally propagated sweet potato cultivars under field conditions. In the laboratory experiment, leaf explants from sweet potato cultivars Mugande, SPK004, Kemb10, Japon tresmesino and Zapallo were tested on media supplemented with six concentrations of 2,4-Dichlorophenoxyacetic acid (2,4-D) (0, 0.5, 1.0, 2.0, 3.0 and 5.0 mg L-1). The cultures were set as a Completely Randomised Design (CRD) in factorial arrangement replicated three times. Calli incidences were significantly (P < 0.05) higher at 0.5 mg L-1 and 1.0 mg L-1 2,4-D levels. These concentrations were used to further study production of plants using the regeneration methods callus induction and somatic embryogenesis. The number of plants regenerated varied significantly (P < 0.05) with the regeneration method and the 2,4-D levels. The highest number of plants was obtained at 0.5mg L-1 2,4-D levels. For both studies, Zapallo was most responsive in all variables measured followed by SPK004 using callus induction method. A field experiment was set up as a Randomised Complete Block Design (RCBD) replicated three times, with the five cultivars germinated and raised under two regeneration methods. Under the field study, significant (P < 0.05) interaction was detected between the test cultivars and regeneration method. SPK004 gave the highest score for the growth variables plant stand count and height, while for the number of branches and leaf area Mugande outperformed all cultivars. The highest marketable and total yield was recorded with Zapallo. Despite conventional propagation method giving higher growth rates the difference in yield between the propagation methods did not vary significantly (P < 0.05). Virus detection for Sweet Potato Feathery Mottle Virus (SPFMV) established that field plants had a higher virus titre compared to the tissue culture regenerated plants. From the study, regenerating Zapallo using callus induction method at 0.5 mg L-1 2,4-D levels gave lower disease ratings and subsequently highest marketable number of tubers therefore callus induction is recommended as the most suitable regeneration protocol for the local sweet potato cultivars.