Effects of Magnetic Field Exposure and Growth Regulators on Callus Induction and Shoot Regeneration in Barley (Hordeum vulgare L.) Embryo Culture

Magnetic field (MF) exposure has been increasingly explored as a physical factor associated with altered morphogenic responses in plant tissue culture systems. This study investigated the effects of different MF exposure durations, applied at the seed stage, in combination with plant growth regulators (PGRs) on callus induction, shoot regeneration, rooting, and acclimatization in barley (Hordeum vulgare L.) immature embryo cultures. Following MF treatment, seeds were grown under normal conditions, and immature embryos were subsequently isolated and cultured in vitro. Three cultivars (Aydanhanım, Baronesse, and Bolayır) were evaluated under MF treatments (0, 24, 48, and 72 h) and various auxin–cytokinin combinations. The results revealed pronounced genotype-dependent responses to both MF exposure and PGR composition. Dicamba consistently promoted higher callus induction across all cultivars, whereas the effectiveness of 2,4-dichlorophenoxyacetic acid (2,4-D) was markedly reduced, particularly in Baronesse. MF exposure was associated with increased callus fresh weight in Bolayır and Baronesse, especially under longer exposure durations. Optimal shoot regeneration was generally obtained with 48-h MF exposure combined with moderate 6-benzylaminopurine (BAP) concentrations (0.1–0.5 mg L⁻¹), although the optimal MF duration varied among cultivars. Rooting responses were also genotype specific: Bolayır exhibited successful rooting under all MF treatments, whereas Baronesse required prolonged MF exposure, and no rooting was observed in Aydanhanım. Although flowering occurred during acclimatization, endosperm development was not detected in any treatment group, including the MF-free control, suggesting that this outcome may reflect physiological constraints associated with the in vitro regeneration process rather than MF-specific effects. Overall, these findings emphasize the importance of genotype-specific optimization of MF duration and PGR composition in barley tissue culture and highlight the need for further molecular studies to elucidate MF-associated physiological and regulatory mechanisms.