Effect of different combinations of plant growth regulators on in vitro propagation of yam (Dioscorea spp.)

Abstract

Yam is a multi-species tuber crop cultivated in Africa, Asia and parts of South America. It is an important crop in South and Southwestern parts of Ethiopia. Yam is propagated from seed tubers or sections of tuber and corms. Seed tubers are expensive, bulky to transport and the multiplication rate in the field is very low. Shortage of seed tubers for planting is one of the major constraints for yam production in Ethiopia. To overcome such problems and to increase production, in vitro propagation has been implemented for many Dioscorea species. However, no information is available on work done on micropropagation of Dioscorea spp. in the country. The current study was, therefore, initiated to optimize type and concentration of plant growth regulators for shoot multiplication and rooting. Two experiments: shoot multiplication and rooting in vitro were carried out using a completely randomized design with five replications. For shoot multiplication, shoots initiated from nodal cuttings were treated with BAP in combination with NAA. For rooting, the micro-shoots were transferred to ½ MS media containing NAA and IBA. Data on number of shoots per explant, roots per shoot and related growth parameters were recorded and statistically analyzed. The results showed that MS media supplemented with 1.5mg/l BAP + 0.15 mgl-1 NAA gave an average of 6.40±0.28 shoots per explant with a mean shoot length of 2.0±0.11 cm. MS supplemented with BAP (1.0 mg l-l) and NAA (0.15 mg l-l) gave 5.40±0.28 with a mean shoot length of 1.84±0 .20 cm. There was no shoot growth on basal media without plant growth regulators, showing that cytokinin is needed to initiate multiple bud formation in the genotype. Plantlets grown on half strength MS media supplemented with 2.0 mg l-l NAA and 0.5 mg l-l IBA produced 5.7±0.27 roots per plantlet and an average root len gth of 4.63±0.23 cm. The second highest root number was recorded on 1/2 MS with NAA (2 mgl-1) and IBA (0 mg l-1), with an average of 4.8±0.27 roots per plantlet and an av erage root length of 3.52±0.20 cm. Thus MS media supplemented with 1.5mgl-1 BAP and 0.15 mg l-l NAA can be recommended for shoot multiplication of this yam variety and 1/2 MS supplemented with2.0 mg l-l NAA and 0.5 mgl-1 IBA for in vitro rooting. Besides the need of further optimization of this protocol, similar protocols for the other yam landraces are required.