Overcoming Shoot Regeneration Recalcitrance of Solanum quitoense L. via Combined Application of Gibberellic Acid (GA 3 ), Thidiazuron (TDZ), and Naphthaleneacetic Acid (NAA)

Solanum quitoense L. an Andean fruit species of high nutritional and agro-industrial value, exhibits notable recalcitrance to in vitro shoot regeneration, which limits its biotechnological exploitation and the development of genetic improvement programs. This study evaluated the effects of different combinations of thidiazuron (TDZ) and naphthaleneacetic acid (NAA), in the presence or absence of gibberellic acid (GA3; 1.0 mg/L), on the morphogenic response of cotyledon and hypocotyl explants. The evaluation was conducted over 10 weeks, considering necrotic explants, callus induction, rhizogenesis, shoot regeneration, and number of shoots per explant. GA3 supplementation markedly improved the morphogenic response of S. quitoense, although the response was explant-dependent. The highest overall shoot regeneration rate was obtained in hypocotyl explants cultured with GA3 (1.0 mg/L) + TDZ 0.10 mg/L without NAA, reaching 57.8%. In cotyledon explants, the best response was achieved with GA3 (1.0 mg/L) + TDZ 0.50 mg/L + NAA 0.01 mg/L, reaching 42.2%. In contrast, treatments without GA3 predominantly led to necrosis and callogenic responses, with null or extremely limited shoot regeneration. This study represents a significant advance in the in vitro regeneration of a tissue culture–recalcitrant species by identifying GA3-containing hormonal combinations that improve shoot regeneration. These findings provide a useful framework for developing regeneration protocols applicable to micropropagation, breeding, and genetic transformation of S. quitoense.