Application of plant biotechnology for breeding of Ipomoea species

In this study, I tried to establish the necessary protocols for the application of plant biotechnology to breeding of two Ipomoea species, I. batatas (sweet potato) and I. trichocarpa. The results obtained are summarized as follows: (1) High frequency of plant regeneration from leaf calli of sweet potato: High frequency plant regeneration was established from leaf calli of sweet potato (Ipomoea batatas (L.) Lam.) cv. Chugoku 25. Calli were formed from leaf segments on LS medium supplemented with 0.5 mg/l 2,4-D, 3,000 mg/l yeast extract, 5% (W/V) sucrose and 0.25% (W/V) gellan gum. Plant regeneration occurred at the frequency of more than 25% by transferring the calli onto the regeneration medium which was LS basal medium without any plant growth regulators. The presence of either abscisic acid (ABA) or silver nitrate (AgNO3) in the callus induction medium promoted shoot regeneration. The optimum concentration was 2 mg/l for both ABA and AgNO3, the frequency of plant regeneration being 70 and 73.3%, respectively. (2) Plant regeneration from leaf calli of Ipomoea trichocarpa Ell.: Calli were induced from leaf pieces of Ipomoea trichocarpa on the LS basal medium supplemented with 0.5 mg/l 2,4-D, 5 mg/l ABA, 3 g/l yeast extract, 5% sucrose and 0.2% gellan gum. These calli formed adventitious buds on the regeneration media containing more than 2 mg/l BA. The highest adventitious bud formation was obtained at 10 mg/l BA. Adventitious root were also produced from calli on all kinds of the regeneration media used in the present study. There are two type of the adventitious roots from leaf calli, thick roots (1.0 mm n diameter) and thin roots (less than 0.2 mm in diameter). When the calli with adventitious roots were transferred to plant growth regulator (PGR)-free LS medium, 63.3-90.6% of the roots produced shoots