In vitro Regeneration of Abelmoschus esculentus L. cv. Wufu: Influence of Anti-browning Additives on Phenolic Secretion and Callus Formation Frequency in Explants

Okra (Abelmoschus esculentus L.) belongs to the Malvaceae family and is a difficult species to manipulate and regenerate in vitro. In this study, factors that influence secretion of phenolic compounds, callus induction, and subsequent regeneration in okra were optimized. Different concentrations of anti-browning additives, such as activated charcoal (AC) and citric acid (CA) were tested alone or in combination with ascorbic acid (AA) in MS medium to evaluate their ability to control phenolic secretion from hypocotyl and cotyledon explants. Among the anti-browning additives, 200 mgL-1 AC and 10 mgL-1 CA + AA (1:1) were best at controlling phenolic secretion from hypocotyl and cotyledon explants in callus induction medium. Hypocotyl explants were more suitable for callus initiation and organogenesis than cotyledon explants. Moreover, among twelve types of media tested for callus culture, the addition of 0.5 mgL-1 2,4-dicholorophenoxy acetic acid (2,4-D) and 1.5 mgL-1 benzyladenine (BA) to the growth media was the most effective for hypocotyl explants, whereas MS + 1.5 mgL-1 α-naphthylacetic acid (NAA) and 0.5 mgL-1 6-benzyloaminopurine (BAP) was effective for cotyledon explants. Improved shoot regeneration was achieved with 2 mgL-1 BAP and 0.1 mgL-1 indole butyric acid (IBA). The maximum number of strong and healthy roots was obtained on media that included 2 mgL-1 IBA and 200 mgL-1 AC. Rooted plantlets were successfully acclimatized in earthen pots, and the rooted plantlets had normal morphology and growth characteristics. The present study offers a potential solution for controlling phenolic secretion during okra regeneration using additives and evaluates the manipulation of plant growth regulators for effective regeneration of the Wufu okra cultivar.