**3.1.1 Pregowth**

Water contents of Frafra potato nodal cutting explants following pregrowth on medium supplemented with 0.058 M (2%) sucrose was extremely high (22.25+1.7 gH2O g-1 dry wt) to enhance successful cryopreservation. As explant size and geometry have a marked effect on the success of freezing hydrated material (Wesley-Smith *et al*., 1995), nodal cuttings (two buds per explant) to be used for cryopreservation experiments were split into two halves with one bud per explant, this adequately lowered water content of explants (8.78±1.07 gH2O/g dry wt). The water content of the single (well trimmed) bud is similar to that of explants excised from greenhouse established plant (10.16±0.98 g/g dry wt. data shown in Table 2). Since cultures grown on medium supplemented with 2% sucrose were extremely wet for cryopreservation, higher sucrose or mannitol concentration (0.1 M) was employed to enhance desiccation tolerance, which subsequently improves cryotolerance .

Pregrowth of explants on medium supplemented with 0.1 M mannitol lowered the water content of explants from 19.5 under control condition (medium supplemented with 0.058 M sucrose), to 10.4 gg-1, which did not affect survival (Fig. 1). The ultrastructure was as well constituted as that of the control explants (Plate 1a), with ongoing metabolism indicated by abundant cristate mitochondria (Plate 1b), Golgi bodies and profiles of endoplasmic recticulum (insert). Growth on 0.1 M sucrose supplemented medium, also lowered the water content of explants (11.4 gg-1) as shown in Fig. 1, this observation is in agreement with response of oil palm explant water content when treated with sucrose (Dumet *et al*., 1993) and while this did not reduce survival it resulted in severely distended organelles and evidence of tonoplast disruption and lobed nuclei (Plate 1d and e). Sucrose has been extensively used to treat plant tissues prior to cryopreservation (Panis *et al*., 2002; Grospietsch *et al*., 1999; Gonzalez-Benito & Perez, 1994; Santos & Stushnoff 2003), studies have however, not investigated the structural effect of sucrose on tissue. The damage revealed by ultrastructure (Plate 1f) could have predisposed explants negatively to subsequent steps.
