Abstract

Osmotic stress is a major abiotic constraint that limit ornamental plant growth and quality. Con-ventional breeding for osmotic tolerance is restricted by lengthy breeding cycles, highlighting the need for alternative strategies such as in vitro mutagenesis combined with osmotic screening. The ornamental crop gerbera(Gerbera jamesonii) is highly sensitive to water deficit. In this study, four-week-old in vitro shoot clusters of G. jamesonii "Jent" were treated with N-nitroso-N-methylurea (NMU) or sodium azide (NaN3) at concentrations of 0.05–0.25% for 5–20 min and then cultured on MS medium supplemented with 40 g/L mannitol to simulate osmotic stress. Regeneration frequency, growth traits, photosynthetic pigments, gas exchange, and biochemical markers were evaluated six weeks after treatment. Regeneration declined with increasing mutagen concentratio-nand exposure time, with the sharpest reduction observed at 0.20–0.25% for 20 min. Four osmotic-tolerant lines were identified, three derived from NaN3 treatment and one from NMU treatment. Under osmotic stress conditions, Lines 1 and 2 (NaN3, 0.15% for 15 min) exhibited superior per-formance, maintaining leaf area and fresh weight at levels comparableto those of non-mutagen-treated shoots under non-stressed conditions. These lines maintained higher chlorophyll levels and displayedonly approximately15% reduction in photosynthesis, without asignificant increase in respiration. oluble sugar and proline contents, particularly in Lines 3 (NaN3, 0.15% for 20 min) and 4 (NMU, 0.10% for 20 min), increased under osmotic stress, whereasstarch and protein contents de-creased, most notably in Line 4. Our findings indicate that NaN3 treatment, particularly at 0.15% for 15 min,is an effective condition for generating osmotic-tolerant gerbera lines, providing promising germplasm for future breeding and functional studies.