Protocol Optimization for In Vitro propagation of Sweet Potato (Ipomoea batatas L.) Varieties Using Shoot Tip Culture”

Abstract

Conventional propagation methods of sweet potato (Ipomoea batatas L.) through stem cutting requires large amount of materials and space and an extended period to produce plants. There is also a high risk of disease transmission from generation to generation. In vitro propagation is the best alternative to overcome such limitations of conventional propagation. Thus, this study was conducted with the aim to optimizing a protocol for in vitro propagation of sweet potato varieties. For shoot initiation, shoot tip explants of Kulfo and Tulla varieties, the explants were cultured on MS basal medium that contained 30 g/l sucrose and 8 g/l agar supplemented with 0.0, 0.5, 1.0 and 2.0 mg/l BAP. For shoot multiplication, the initiated shoots were cultured on MS medium supplemented with 0.0, 0.5, 1.0, 1.5 2.0, 2.5 and 3.0 mg/l of BAP were used. For in vitro root inductions, micro-shoots were cultured on 1/2 MS media supplemented with 0.0, 0.1, 0.5, 0.75 and 1.0 mg/l IBA while for ex vitro rooting, in vitro multiplied micro- shoots were carefully excised and directly transferred to greenhouse for rooting as well as hardening simultaneously. Among BAP concentrations used for initiation, growth regulators free media resulted in 66.67% and 55.56% for Kulfo and Tulla respectively. Best shoot multiplication (5.33±0.00) shoots/explant with 7.82±0.02cm shoot length and 6.33 ±0.34 leaves/shoot was obtained on MS medium containing 1 mg/l BAP for Kulfo, while 2mg/l BAP resulted in a maximum of (6.78±0.19) shoots/explant with 9.70±0.00cm shoot length and 9.67±0.06 leaves/shoot for Tulla. The best in vitro rooted shoots was 100% with (8.27±0.05) cm root length for Kulfo and 88.89% with 8.24±0.05 cm root length for Tulla, on growth regulators free ½ MS medium. In ex vitro rooting experiment, best rooting response was 93.33% with 3.85±0.00 mean number of roots per shoot and 9.80±0.00 cm root length for Kulfo, whereas Tulla produced 86.70% rooted shoots with 2.52±0.00 number of roots and 8.40±0.00 cm root length. Among all plantlets planted in the glasshouse, 84% and 80% for in vitro rooted shoots, 93% and 86% for ex vitro shoots of Kulfo and Tulla varieties respectively were survived. It could be concluded that in vitro initiation of varieties Kulfo and Tulla, supplemented with BAP free MS media were the optimal concentrations. MS+1mg/l BAP was the optimum concentration for shoot multiplication of Kulfo, while Ms+2mg/l BAP was optimum for best multiplication of Tulla. For in vitro rooting, PGR free ½ MS medium were optimal for Kulfo and Tulla genotypes. Finally, further studies will be needed in ex vitro root induction rather than in vitro rooting for the sake of labour, time, better rooting system and cost reduction.