Selection and regeneration of purple sweet potato calli against drought stress simulated by polyethylene glycol [version 1; peer review: 1 approved with reservations]

Background: Water shortage due to natural and/or technical drought stress, widespread throughout Sumatra, Java, Sulawesi and Kalimantan islands, significantly reduces crop production. The development of varieties tolerant to drought stress is important since it is more effective rather than improving irrigation infrastructure to increase the sweet potato productivity. Methods: Selection and regeneration experiments assessing purple sweet potato callus tolerance of drought stress, simulated by polyethylene glycol (PEG), were conducted to generate new variant plants tolerant of drought stress. Sterile explants (leaf and petiole) generated from previous in vitro culture were inoculated to the Murishage and Skoog (MS) medium containing plant growth regulator combination as treatments to induce calli. The calli were then transferred to half-MS medium containing 0, 5, 10, 15 and 20% PEG as selection agent for drought tolerance. The surviving calli were regenerated in the MS medium containing 0, 0.5, 1 or 1.5 mg l -1 6-benzylaminopurine (BAP). The callus formation, growth and survivability during in vitro culture were measured. Results: Calli were successfully formed in almost all media containing 2, 4- Dichlorophenoxyacetic acid (2,4-D ) with the concentration of 1, 2, 3 and 4 mg l -1 and BAP (concentration: 0.5 and 1 mg l -1), but the medium of MS + 2 mg l -1 2,4-D + 0.5 mg l -1 BAP resulted in the highest number of induced calli per treatment (mean=11.36), with the percentage of responsive explants standing at around 96%. The higher the concentration of PEG, the lower the number of surviving calli. At 20% PEG, only 54.42% calli survived. There were five plants successfully regenerated from the survived calli at 20% PEG, using MS medium containing 1.5 mg l -1 BAP. Conclusions: The experiment has successfully produced putative drought-tolerant plants by callus screening using PEG as drought-tolerance-selecting agent in purple sweet potato.