In vitro propagation of enset (Ensete ventricosum (Welw.) Cheesman)
Enset (Ensete ventricosum) is an important food crop that is cultivated in Ethiopia. In vitro propagation: zygotic embryo culture, shoot tip culture, callus culture and somatic embryogenesis were investigated for this crop. Forty four percent germination of excised embryos of stored seeds of enset genotype Oniya was obtained when the embryos were placed horizontally on the medium that was supplemented with 0.5 mg l ̄¹BA and 0.2 mg lˉ¹ lAA, after germination of intact seeds could not be achieved. Over 85% embryos, excised from seeds of two wild enset genotypes shortly after seed harvest, were germinated on MS medium with and without plant growth regulators (PGRs). Addition of 5 g lˉ¹ activated charcoal (AC) prevented blackening of germinating zygotic embryos and improved in vitro growth of the seedlings. Contamination of culture was reduced to a tolerable level (below 7%) when eight to ten mm long shoot tips from greenhouse-grown suckers were decontaminated for 15 min in 3.5% sodium hypochlorite and rinsed three times with sterile distilled water. However, this contamination method was not sufficient to decontaminate shoot tips from field-grown suckers. Avoiding injury to the apical domes of the shoot tips at the initiation stage, addition of 7 g lˉ¹ AC to the medium and initiation of the shoot tips for two months before splitting for multiplication considerably decreased blackening and formation of callus for genotype Keberia and Mazia. Three to five normal shoots per shoot tip were produced when halved shoot tips from in vitro germinated seedlings of enset genotype Oniya was cultured on gelled and in liquid medium and when halved shoot tips of greenhouse-grown genotype Mazia were cultured in a liquid medium. One to two shoots/buds per shoot tip were regenerated from halved shoot tips of greenhouse-grown suckers on gelled medium for genotypes Keberia, Oniya and Mazia. The presence of BA did not result in a significant increase in the number of shoots per shoot tip both with intact and halved shoot tips. Therefore, wounding the apical dome by splitting appears necessary to release lateral buds. Both blackening of explants in the presence of AC and contamination of culture in vitro were not observed with in vitro grown plant material. Callus was produced on MS medium supplemented with 0.5 mg lˉ¹ BA + 0.2 mg lˉ¹l lAA from zygotic embryos of stored seeds of enset. Adventitious shoots from the callus were regenerated in the light on MS medium lacking PGRs. Embryogenic callus was obtained from shoot tips of genotype Mazia on MS medium with 0.5 mg lˉ¹ BA + 0.2 mg lˉ¹ lAA + 0.2 mg l ˉ¹2, 4-D. A large number of somatic embryos were produced from the embryogenic callus. The results of these studies can be used in enset clonal multiplication, conservation of germplasm and breeding of the crop.