| The optimum temperature for Tomato growing is between 22-28℃.If the temperature is less than 15℃or above 28℃,the flower and fruit may drop.When the temperature reached above 30℃, its assimilation decreased significantly.When it increased above 35℃,the reproductive growth is disturbed and destructed.Even the temperatures gets 45℃in a short period time,tomato also have physiologically disturbance,resulting in flower and fruit dropped or undergrown.Tomato grows difficultly in the south of the hot wet region in summer;the production season is generally spring to summer and autumn to winter.As the protected cultivation developed,vegetable production is usually in out-of-season,with the application of mulch,shade nets,plastic greenhouses,greenhouse, vegetable growth environments have been improved greatly.This makes vegetable cultivation period extended and market time increased.As global temperature goes warming prominently,the temperature under protected cultivation in southern provinces in summer are unusual and sustained high.The growth of the tomato gets seriously damaged,resulting in reduced yield.This would result a great loss to producers and consumers.So the production of tomato in heat summer becomes an important job.Hardening,shading and ventilation have been used to increase the ability of seedling heat-resistant.The morphology,physiology,biochemistry,signal transduction and gene expression of tomato in heat stress become more and widespread concern problems with many scholars.As a new type of plant growth regulator,Salicylic acid and Chitosan have some response to adversity environment;and there is little research on the heat resistance of tomato which is pretreatment with Salicylic acid and Chitosan.The experiment studied the tomato seedling ability of heat resistant with pretreatment by spraying Salicylic acid and Chitosan and their mixture under heat stress.Further,the physiological and biochemical changes,antioxidant enzyme system and metabolism had been studied after applying of their mixture.This was an attempt to providing in-depth theoretical basis with tomato breeding,cultivation in summer heat stress,to increase ability of resistance under heat stress.The results as follows:1.Application of 60 mg·L-1salicylic acid and 90 mg·L-1chitosan can significantly reduce the leakage of electrolyte,reduce peroxidation product of MDA,raise leaves Proline content,slow down the decomposition of chlorophyll,and ease the harm of high temperature to tomato seedlings.2.Application of the mixture of 60 mg·L-1salicylic acid and 90 mg·L-1Chitosan can also reduce the leakage of electrolyte,reduce peroxidation product of MDA,raise proline content and slow down the decomposition of chlorophyll under heat stress.It proves mixture can induce tomato to enhance resistant under heat.3.The pretreatment can increase the activity of SOD,POD,CAT,and APX,reduce the injury of reactive oxygen.It explains that pretreatment enhanced the ability of heat resistant with increasing of the enzyme activity and keeping stabilization of cell membrane,so increasing the resistance to heat,promoting the growth of tomato seedling.4.Through statistical analysis test,there is no significant difference between spraying any single regulator and their mixture.And there is no any extent effect or antagonism.Maybe there are still some discrepancies with concentrations,and this need further study.
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