Tissue culture techniques for rapid propagation of selected cassava (manihot esculenta crantz) genotypes

This study was conducted in the Plant Tissue Culture Laboratory of the Agricultural Research Corporation (ARC) during 2005 to 2008 to develop in vitro propagation techniques for cassava genotypes. The effects of different nutrient media formulations (Gamborg et aI., 1968 called B5; Murashige and Skoog, 1962 called MS and Schenk and Hildebrandt, 1968 called SH) on micropropagation were tested. Murashige and Skoog was the best medium for propagation of cassava and the cassava genotype Abili had the best shoot morphogenesis. Different ratios of wheat flour and agar (70g flour, 70g/2g, 60g/3g, 40g/4g and 8g/l agar) as nutrient media supporting gelling agent were tested on four cassava genotypes. The best shoot induction from nodal explants of selected cassava genotypes was found on MS medium gelled with 60g and 40g/l wheat flour mixed with 3g and 4g/l agar, respectively. Shoot morphogenesis of cassava genotype Abili was significantly better than all other genotypes. The effects of three cytokinins i.e. BAP, kinetin and 2ip each at 0.0, 0.05, 0.1, 0.25 and 0.5mg/l on in vitro propagation of nodal explants of cassava genotypes Movondo, Mape, Ziraa and Abili were tested. Significant effects of different concentrations and types of cytokinins were found on all parameters. The percentage of explants with shoots, number of shoots, and number of nodes per explant and height of plantlets were significantly higher on MS medium supplemented with 0.25mg/l and 0.5mg/l BAP. The cassava genotypes Abili and Movondo produced significantly higher number of shoots than Mape and Ziraa. However, cassava genotypes were comparable in numbers of shoots induced per nodal explant, except Mape and Abili, which were the least in terms of number of shoots produced on MS medium supplemented with kinetin and 2ip, respectively. Shoot induction was also tested on MS media supplemented with three auxins (IAA, NAA and IBA) each at 0.0, 0.02, 0.04 and 0.06mg/1 combined with 0.25 and 0.5mg/l BAP using nodal explants of four selected cassava genotypes. The MS medium without auxins was the best in induction of shoot morphogenesis. The effects of IAA and IBA each at 0.0, 0.02, 0.04 and 0.06 mg/l on in vitro root induction of plantlets regenerated from 4 selected cassava genotypes were examined. Significant differences between the different concentrations of the auxins were observed in the number of roots per explant. IAA at 0.02mg/l was the best for cassava genotypes Movondo and Abili, whereas IBA at 0.04 was the best concentration for rooting of short maturing cassava genotypes, Ziraa and Abili and 0.06mg/l IBA was the best for long maturing genotypes, Movondo and Mape. Callus induction was investigated with 2,4-D at 0.5, 1.0, 1.5, 2.0 and 2.511, and three types of explants (internodes, leaf petioles and mid-leaf veins slices). Concentrations of 2,4-D were significantly variable in percentages of callus induced per explant. Concentrations 1.5m and 2.0mg/l2,4-D were the best and low percentages of embryogenic callus were induced from it. The effect of explant type was not significant on percentages of the callus induced. However, leaf petioles and mid-leaf veins slices induced medium to large, friable, and grey callus, which was the best characteristic. Effects of growth media substrates i.e. peat moss, riverian (silt)/sand (1:1) and silt soil on in vivo survival of plantlets were tested. There were significant differences in the effects of growth medium substrates on survival and peat moss was the best. Plantlets were transplanted on peat moss and tested under two different conditions (plastic sheet covered and open buckets) and the best survival percentages were found on covered plantlets. The survival of plantlets regenerated on MS medium supplemented with charcoal was significantly higher than those regenerated on MS medium without charcoal