Growth inhibition and recovery of hop (Humulus lupulus L.) under mannitol- and sorbitol-induced osmotic stress in vitro

Abstract

Aim. To model water deficit in hop (Humulus lupulus L.) in vitro using mannitol and sorbitol and to evaluate genotype-dependent growth responses and recovery capacity. Methods. Six-week-old plants of two hop genotypes were cultured on modified Murashige and Skoog medium. Osmotic stress was induced by mannitol or sorbitol (0.01–1.0 M). Shoot height, callus formation, root number and length, and tissue water content were assessed during six weeks of cultivation. Recovery was evaluated after transfer to standard medium. Results. Both polyols induced concentration-dependent inhibition of shoot and root growth and reduced tissue water content. Mannitol caused stronger growth suppression than sorbitol at equivalent concentrations. Moderate sorbitol levels had limited effects on shoot growth and stimulated root development in some genotypes. Growth inhibition correlated with reduced tissue water content. Stress induced by moderate sorbitol concentrations was largely reversible, and transferred plants resumed active growth, in some cases exceeding control performance. Conclusions. Genotype-dependent differences in osmotic stress tolerance were revealed. Polyol-induced osmotic stress in vitro represents a practical approach for preliminary screening of hop genotypes for drought tolerance under climate change conditions.