Effects of multiple factors on hyperhydricity of Allium sativum L.

Hyperhydricity is a common physiological disorder during plant in vitro culture and seriously affected regeneration and micropropagation of plants. Garlic is very susceptible to hyperhydricity. However, effects of multiple factors on hyperhydricity of garlic remain unclear. To clear the regularity of occurrence of hyperhydricity and to obtain a high-efficiency regeneration system of garlic, we systematically investigated effects of explants, media components, culture conditions, and exogenous additives on hyperhydricity. Our results showed that shoots were more easily hyperhydric than plantlets. Shoots induced by inflorescences showed a higher hyperhydric rate and proliferation coefficient than those induced by bulbs. Genotype, physiological age, and explant size affected hyperhydricity of shoots in initial culture, not that of plantlets in subculture. Younger inflorescence and smaller explant were more easily hyperhydric. Dose-dependent manners of cytokinins and gelling agents involved in hyperhydricity were found. Hyperhydricity was aggravated at increased cytokinin concentrations and was alleviated by increased gelling agent and sucrose concentrations, ventilation, and illumination intensity. Media with pH higher than 6.0 and lower than 5.8 resulted in more hyperhydricity. Shoots and plantlets were much more likely to be hyperhydric in MS medium than that in B5 medium. Hyperhydricity was relieved by 50 μM salicylic acid, 250 μM ascorbic acid, 10 μM spermidine, and 50 μM hydrogen peroxide, but aggravated by high concentrations of hydrogen peroxide and spermidine. Mannitol had no effect on hyperhydricity, whereas polyethylene glycol 6000 induced it. Positive correlations of shoot proliferation and hyperhydricity were found under different treatments of cytokinins, gelling agents, and explants which included genotype, organ type, physiology age and size. A regeneration system of garlic with high proliferation coefficient and low hyperhydric rate was established based on the results above.