Exogenous spermidine and calcium alleviate waterlogging stress in cherry tomato at the seedling stage

The cherry tomato (Solanum lycopersicum L.) seedling stage frequently experiences waterlogging due to heavy autumn rainfall in tropical areas, which impairs cherry tomato growth and development. In this study, we investigated the effects of exogenous spermidine and calcium on the morphological, physiological and biochemical traits of two popular cherry tomato cultivars (Hongfei6: flooding-insensitive and Qianxi: flooding -sensitive) to 14 days of waterlogging at the 4 expanded leaves stage under a controlled environment. Overall, waterlogging significantly increased the rate of superoxide radical production, destroyed the photosynthetic system, reduced dry matter accumulation, and suppressed growth in the two cultivars. After foliar spraying once with spermidine or calcium of plants under waterlogging, an extensive lysigenous aerenchyma in the roots formed. Also, the actual photochemical efficiency and potential efficiency (Fv/Fm) of photosystem II in the light, the activities of superoxidase dismutase (SOD) and peroxidase (POD), and Pro and soluble sugar contents in the leaves increased. Thus, plant height, stem diameter, root length, root surface, root volume and plant dry weight were increased after spermidine or calcium application. Compared with the exogenous calcium, the exogenous spermidine could better maintain the integrity of root cells and the normal morphology and function of the root, increase the activities of SOD and POD and plant dry weight. Thus, exogenous spermidine and calcium suppress waterlogging stress with distinct mechanisms and that the protective effect of exogenous spermidine is greater than that of calcium.