Efficient conditions for in vitro establishment and regeneration of disease-free Ugandan farmer-preferred cassava genotypes

Abstract

Cassava (Manihot esculenta Crantz) is majorly devastated by two viral diseases, cassava brown streak disease (CBSD) and cassava mosaic disease (CMD), resulting in 100% yield loss. Being a clonal plant, nodal cuttings (NC) and shoot apical meristems (SAMs) are the best explants for production of disease free planting materials. In this study, NCs and SAMs were used to determine reliable indicators for successful in vitro establishment of cassava. Eight cassava genotypes were used for the study. Leaf samples were collected from 30 stakes of each of the eight genotypes planted in the screen house. The leaf samples were pooled and screened for presence and/or absence of CBSD and CMD by PCR using virus specific primers. Nodal cuttings were excised from screen house grown plants, surface sterilized to rid-off contaminants and established on Murashige and Skoog (MS) Medium. Using the sprouted stakes, 5-mm sized SAMs were excised, surface sterilized and reduced to 0.5-1 and 2-3 mm sizes. The SAMs were established on MS medium with varying concentrations of plant growth regulators (0.5, 1, 2) ml/L Benzylaminopurine (BAP) and (2, 4) ml/L Naphthalene acetic acid (NAA), Kinetin (K) and BAP respectively. PCR results revealed the pooled leaf samples were free of both CBSD and CMD for all genotypes. Establishment and regeneration of NCs was possible with MS medium for all genotypes. For the SAMs, the concentrations of (2, 4) ml/LBAP followed by 2 ml/LNAA facilitated their establishment and regeneration in comparison to KIN.SAMs of 2-3 mm sizes regenerated better than 0.5 - 1 mm size. Both NCs and SAMs of the different genotypes produced leaves, nodes, roots and there was an increase in plant length. These parameters are critical indicators for in vitro establishment and regeneration of cassava.