Protocol optimization for in vitro propagation of Kulfo, orange flesh sweet potato (Ipomoea batatas) variety using shoot tip culture

Conventional propagation methods of sweet potato (Ipomoea batatas L. var Kulfo) through stem cutting require large amount of propagules and large space for preparation. It has high risk of disease transmission to the next generation. In vitro propagation is the best alternative to overcome such limitations. This study was conducted to optimize protocol for in vitro propagation of Kulfo sweet potato variety using 6-benzylaminopurine (BAP) and indole-3-butyric acid (IBA) phytohormones for shoot multiplication and rooting, respectively. The result revealed that the highest shoot initiation (77.78%) and shoot length (4.40 cm) was observed in MS media supplemented with 0.5 mg/l BAP. Best shoot multiplication (5.33 shoots per explants) was obtained in MS medium supplemented with 1 mg/l BAP. MS medium supplemented with 0.5 mg/l IBA showed 100% rooting and average root length of 7.44 cm in vitro. In ex vitro conditions, 93.33% rooting was recorded. During acclimatization, 84 and 93% survival of in vitro and ex vitro rooted plantlets, respectively, were recorded. It could be concluded that MS media without BAP provides optimal condition for shoot initiation. MS supplemented with 1 mg/l BAP provides optimum condition for shoot multiplication. The ex vitro rooting could be better option to reduce in vitro rooting cost and for increased plantlet survival during acclimatization. Based on the result, 0.5 mg/l BAP for shoot initiation, 1 mg/l BAP of shoot multiplication and directly transferring to soil for rooting was recommended for micropropagation of Kulfo sweet potato variety. However, further studies will be needed in ex vitro root induction.   Key words:  Sweet potato, micropropagation, shoot tip culture.