Development of in vitro propagation protocol for some recalcitrant cassava (Manihot esculenta Crantz) genotypes in Sierra Leone

A study on rapid propagation of cassava through tissue culture was conducted with three elite cassava genotypes: Slicass 6, Slicass 11 and Cocoa from Sierra-Leone. They showed slow growth in Murashige & Skoog (MS) basal medium which was proven to be optimal for a vast number of cassava accessions. Prior to mutation induction, a large population needs to be produced for mutagen susceptibility test and for mutant population development. The ultimate objective of this study was to investigate the effects of plant growth regulators on the shoot development of three cassava genotypes. In vivo shoot tips were sterilized and sub-cultured on MS media supplemented with six combinations of plant growth regulators (PGRs) at different concentrations. The results showed that from all media used, the MS medium with 1.0 mg/L α-naphthalene acetic acid (NAA) showed the best response for rooting (5.50), fresh weight (0.29 g), root number (10.00) and plantlet height (3.81 cm), while 0.1 mg/L 6-benzylaminopurine (BAP) was found to be more favourable to shoot development of leaves (6.38). The highest plant height and fresh weight were 3.81 cm and 0.29 g, respectively for Cocoa at 1.0 mg/L α-naphthalene acetic acid (NAA), 10.00 roots for Slicass 6 at 1.0 mg/L, 6.37 leaf numbers for Slicass 11 at 0.1 mg/L 6-benzylaminopurine (BAP) and 5.6 at 1.0 and 1.5 mg/L α-naphthalene acetic acid (NAA). These observations indicate that a supplement of 0.1 mg/L 6-benzylaminopurine (BAP) in MS medium can be useful in propagation of recalcitrant cassava and low concentration of α-naphthalene acetic acid (NAA) will be beneficial in root induction prior to acclimatization with promotion in recovery of the ex vitro plants before field assessment. Key words: Cassava, Manihot esculenta, propagation, shoot tip, 6-benzylaminopurine (BAP), α-naphthalene acetic acid (NAA).