Exogenous and endogenous plant growth regulators’ effect on regeneration of selected African sweetpotato (Ipomoea batatas L. Lam) cultivars

Optimization of plant regeneration protocol is a first critical step to facilitate techniques such as transgenesis, cisgenesis and genome editing. In this study, we assessed: i) influence of explant type on regeneration efficiency (RE); ii) RE of 33 sub-Saharan African sweetpotato cultivars; and iii) levels of endogenous zeatin riboside (ZR), indole-3-acetic acid (IAA) and their correlation to RE. Indirect organogenesis was conducted using a 2-step protocol: step-1, explants were cultured on MS containing 0.05 mg L-1 2,4-D for 2 days and transferred to step-2 with MS with 0.2 mg L-1 cytokinin for 60 days. Highest RE was obtained from leaf with petiole explants. High RE of 60–87% was obtained for 3 cultivars, moderate RE >40% for 7 cultivars and low RE 40% were amenable to the 2-step protocol on application of exogenous PGRs; endogenous IAA and ZR levels are genotype-dependent, and higher endogenous IAA levels may contribute to inhibiting regeneration. For the remaining recalcitrant cultivars, we recommend further optimization, paying particular attention to endogenous PGRs that could have synergistic and antagonistic interactions with exogenous PGRs