Factors affecting in vitro propagation of cassava (<i>Manihot esculenta Crantz</i>.) Euphorbiaceae, varieties of ‘Kello’ and ‘Qulle’

Abstract

Cassava (Manihot esculenta Crantz.) is a perennial shrub of the Euphorbiaceae family native of eastern tropical South America, grown in the tropics of Africa and Asia for its tuberous roots. Its cultivation is constrained by several problems including the use of cuttings infected with diseases and pests, the lack of high quality seed, low productivity, high heterozygosity, low fertility, poor seed set and seed germination. The objective of this study was to find the optimal conditions for micropropagation of two varieties of cassava released for farmers for the production of high quality planting materials. These include determination of the effect of temperature on bud-break of mother plants, differences in concentrations of salt, sucrose, and thidiazuron (TDZ) in a semi-solid MS medium, pH, two-step MS medium and repeated subcultures. The mean number of shoots per plant for axillary bud-break was highest (10.8) at 26°C for that from ‘Kello’ and 9.8 at 30°C for that from ‘Qulle’. The highest mean number of shoots per explant was obtained on MS medium containing 0.2 mg/L TDZ for both varieties on both semi-solid and two-step MS medium culture system. Maximum mean shoot number was obtained on MS medium of a quarter and full salt strength for ‘Kello’ and ‘Qulle’, respectively. The highest mean number of shoots per explant for ‘Kello’ (4.10) and ‘Qulle’ (2.40) was obtained at pH 5.6 and 6.6, respectively. ‘Kello’ produced 3.70 shoots per explant on MS medium containing 1.5% sucrose. Repeated subculturing of ‘Qulle’ resulted in gradual loss of multiplication rate from the third subculture onwards. The present study contributes to optimization of micropropagation of cassava.

Key words/phrases: Liquid medium, Salt strength, Shoot multiplication, Sucrose, TDZ.