Calcium Chloride Pretreatment Enhances Waterlogging Tolerance of Chrysanthemum under High Temperatures

Field-grown chrysanthemum [Dendranthema ×grandiflorum (Ramat.) Kitam.] would not grow well or even die in summer heavy rain conditions in subtropical and tropical areas, while exogenous calcium might enhance waterlogging tolerance and alleviate plant damages. The effects of various CaCl₂ concentrations pretreatment were studied on growth and malondialdehyde content in two chrysanthemum cultivars, waterlogging-tolerant ‘Huang Gin-Ging’ and waterlogging-intolerant ‘Kaa Dei-Na’. Vegetative young plants with 14-16 leaves were placed in a phytotron at 30/25 ℃ under natural daylengths (13-13.5 h). Apart from normal irrigation (control), plants were pretreated with 0, 60, 90, or 120 mM CaCl₂, respectively to the medium on 1 and 3 days before subjected to 3-d waterlogging followed by 9-d recovery. For both cultivars, control plants grew well. Plant growth of ‘Hunag Gin-Ging’ did not differ among CaCl₂ pretreatments, while ‘Kaa Dei-Na’ exhibited increased plant height, leaf number, and root dry weight as CaCl₂ concentration increased. Application of 120 mM CaCl₂ pretreatment enhanced growth of waterlogging-intolerant ‘Kaa Dei-Na’ through higher root dry weight and lower malondialdehyde content.