The Effect Of Waterlogging Stress On Seedling Stage Of Cherry Tomato And Its Mitigation Approach

Cherry tomato is one of the most important economic vegetable crops in the world.Due to its excellent taste and nutrition,cherry tomato has been widely cultivated in tropical areas of China in recent years.Affected by the monsoon,the rainfall in cherry tomato seedling stage is frequent in there.In addition,the soil in this area is sticky,the drainage system of farmland is not perfect,and waterlogging occurs frequently.Waterlogging seriously affects the growth and development of cherry tomato and limits its yield and quality.‘Qianxi’,‘Lixinjiaxi’,‘Hongfei 6’,‘Hongzuanshi’and‘Taiwanzanmei’,five common cherry tomato varieties from tropical regions,were selected in this study.Physiological and biochemical indexes of cherry tomato seedlings were determined after different flooded days（0,2,4,8 and 16 d）.This study investigate the response of cherry tomato and its waterlogging tolerance to the number of days under flooding stress at seedling stage.After that,Hongfei 6（high endurance）and Qianxi（sensitive）,were sprayed with 0.25 mmol·L^-1spermidine and20 mmol·L^-1calcium chloride(Ca²⁺)on the surface of leaves before flooding treatment.The morphological characteristics,antioxidant system related enzyme activity,proline,soluble sugar and soluble protein content were measured at different days of flooding（0,2,4,6,10 and 14 d）,At the same time,the anatomical structure of root tip,root morphology,SPAD value,chlorophyll fluorescence parameters,fresh and dry weight of root,stem and leaf were measured at 14 days of flooding.The main results are as follows:1. Under the stress of flooding,the plant height and stem diameter of five cherry tomatovarieties,namely‘Qianxi’,‘Lixinjiaxi’,‘Hongfei 6’,‘Hongzuanshi’and‘Taiwanzanmei’,plantheight and stem diameter decreased gradually compared with CK with the extension of flooding time;The SPAD value of the leaves was relatively stable in the early period of flooding（0～8d）,but rapidly decreased in the late period of flooding;The dry weight of the above ground part and the dry weight of the root system were inhibited to different degrees at the end of flooding,and 5 varieties showed significant differences compared with CK.2. the content of O₂^·—and MDA in leaves of cherry tomato showed a tendency of first risingand then falling in the early stage,while in the late flooding period,the varieties of‘Qianxi’and‘Lixinjiaxi’showed rapid rise and significantly higher than the control after flooding16 days.The superoxide dismutase and peroxidase in leaves showed a trend of gradual increase and then decrease,while the catalase activity of‘Hongfei 6’was significantly higher than the control on the second day of flooding,while others was all lower than the control.However,during the waterlogging stress it was significant for the content of soluble sugar,and proline to increase in the leaves of cherry tomato.the content of soluble protein increased first and then decreased.The content of soluble protein was lower than CK except for red diamond at 16d after flooding.As the flooding days went by,the Root activity increased first and then decreased,and there was a significant decrease in‘Qianxi’and‘Lixinjiaxi’varieties after flooded 16 days.Using Principal Component Analysis（PCA）to comprehensively evaluate the cultivar’s waterlogging resistance:‘Hongfei 6’>‘Hongzuanshi’>‘Taiwanzanmei’>‘Lixinjiaxi’>‘Qianxi’.3. After spermine treatment,plant height,stem diameter and leaf thickness of‘Hongfei 6’and‘Qianxi’,while root length,root surface area and root volume increased.Root,stem and leaf fresh weight and dry weight were increased,the fluorescence parameters of actual light energy conversion efficiency(Ф_PSⅡ),maximum light quantum yield（Fv/Fm）is rising,which is significantly higher than the‘Hongfei 6’flooded water treatment,the coefficient of photochemical quenching（NPQ）significantly reduced;A large amount of lysogenic aerenchyma was formed in the anatomical structure of root system.O₂^·—release rate and MDA content increased first and then decreased with the extension of flooding time;POD,SOD and CAT activities gradually increased;proline and soluble sugar contents in leaves of‘Hongfei 6’first increased and then decreased,while‘Qianxi’gradually increased.4. After calcium treatment,the plant height,stem diameter and leaf thickness of‘Qianxi’increased,while the root length,root mean diameter,root surface area and root volume increased compared with that of flooding.The fresh and dry weight of root and leaf,as well as the fresh weight of stem,were increased,and a large amount of aerolysis tissue was formed in root tip.O₂^·—release rate and MDA content showed an increasing trend,but were still lower than that of waterlogging treatment.SOD,POD and CAT activities first increased and then decreased,which were higher than that of waterlogging treatment at the end of waterlogging.The relieving effect of‘Hongfei 6’was better in the early period of flooding,which could effectively increase plant height,stem diameter and leaf thickness,reduce O₂^·—release rate and MDA content,and improve SOD,POD and CAT activities.However,after flooding,plant height,stem diameter and leaf thickness all decreased,O₂^·—release rate and MDA content increased,and antioxidant enzyme activity decreased.After 14days of flooding,root length and root surface area increased slightly,but root mean diameter was significantly lower than that of flooding.The dry weight of roots,stems and leaves was lower than that of flood treatment;Local parenchyma cells in root tip rupture and dissolve seriously,causing root damage.In addition,two varieties ofФ_PSⅡand Fv/Fm are higher performance,NPQ reduced,proline and soluble sugar content increased significantly.To sum up,flooding stress can slow down the growth of cherry tomato,decrease the biomass accumulation,increase the MDA content and O₂^·—release rate,decrease the photosynthesis,regulate the activity of antioxidant enzyme and osmotic regulating substances.Both spermidine and calcium can effectively alleviate the damage caused by flooding,in which spermidine can prolong the survival of plants by actively regulating the physiological mechanism in the environment with a long period of flooding,while calcium shows a strong mitigating effect in the short term after flooding,but the mitigating effect cannot be maintained under long-term stress.In this study,the relieving mechanism of exogenous spermatine and calcium on waterlogging stress in seedling stage of cherry tomato was investigated,provide a theoretical reference for the selection of cherry tomato cultivars and the mechanism of resistance to waterlogging cultivation in the tropics.