Effects Of Water Stress And Re-water In Different Growth Stages Of Tomato On Physiological Characteristics,Fruit Quality And Yield

Tomato is an important vegetable cultivated in facilities in China,which is very sensitive to water.Tomato has a long growth period and different growth stages have different needs for water.In view of the water demand of tomato,it is of great significance to carry out the effect of water stress on tomato at different growth stages for the conservation and efficient utilization of water resources.The experiment was carried out in the greenhouse in February 2017,with three irrigation treatments full irrigation W(70-80%θ_f),mild water stress W1(50-60θ_f),and moderate water stress W2(40-50θ_f),as well as three growth stages S(at seedling stage),A(at flowering stage),and F(at fruit expanding stage).The effects of continuous 18-day water stress and subsequent 3-day rehydration treatment on physiological characteristics of tomato in three different growth periods were discussed,and the differences and comprehensive rankings of fruit quality and yield of different bunches under each treatment were determined,which laid a foundation for realizing high-quality and efficient production of tomato.The following main conclusions were obtained through the experiment and index observation of tomato cultivation:1、The most of the photosynthetic indicators had a decline trend under water stress,and the value under mild water stress was higher than that of moderate water stress at the same growth stage.Furthermore,all of them recovered to the initial value by and large eventually.The instantaneous water use efficiency(iWUE)peaked at the last day of water stress.There was a significant positive linear relationship between net photosynthetic rate(Pn)and transpiration rate(E),Pn and stomatal conductance(Gs).2、The activities of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)in both tomato leaves and roots increased continuously under water stress conditions at three growth stages and recovered a lot after rehydration.According to the results,the SOD activities in leaves was higher than in roots and the POD,CAT activities in leaves was lower than in roots throughout the whole growth periods.The value of Pn reduced with the increasing of antioxidant enzyme activities with the development of tomato growth period,and the correlation between Pn and antioxidant enzyme activities was highly significant.3、Both the stomatal length(SL)and stomatal width(SW)had a decline trend which was differ from the stomatal density(SD),SD increased during the water stress days.There was a positive parabolic correlation Pn and SW;on the contrary,the negative linear correlation between Pn and SD was highly significant.What’s more,we determined the response of yield and quality of different bunches of tomatoes under water stress during different growth stages.4、In addition,we evaluated the comprehensive fruit quality and yield of the second and third bunch of fruit.The results showed that water stress was important for the improvement of fruit quality,but that yield decreased inevitably during water stress.The fruit quality notably improved SS(soluble sugar),TSS(total soluble solid),VC(vitamin C),and F(firmness)compared to control.The combined effects of water stress and growth stage significantly affected SS and TSS.In the later growth period,water stress significantly improved the content of SS and TSS compared to seedling and flowering stages.There were significant differences between the second and third bunches of fruit in terms of the tomato quality,especially in the content of SS,OA(organic acid)and L(lycopene).Compared with the third bunch of fruit,the second bunch of fruit had better flavor quality and the third had better appearance quality.The yield of the second and third tomato bunch decreased from9.16%to 35.04%and 7.85%to 23.40%compared with control,and the effects of mild water stress on fruit yield were minimal in the early growth stage.5、Principal component analysis(PCA)and grey relational analysis(GRA)were used to evaluate comprehensive fruit quality,and the best treatment in terms of the fruit quality was W1F for both bunches and the average quality of the two bunches.The evaluation of combined fruit quality and yield was carried out using the rank-sum ratio(RSR)method.The best treatment was both W1F of the second and the average quality of the two bunches based on the two methods.W1F treatment was first based on PCA and W1S treatment was first based on GRA in terms of the third bunch.6、Although the water stress had negative influences on physiological indicators of tomato,the effects of water stress on physiological indexes was not irreversible,since these indexes had restored to a certain extent after rehydration.The water stress had a bigger impact on physiological parameters in flowering period than the seedling and fruit expanding period.Based on the comprehensive consideration of the above factors,it was verified that mild water stress had no significant effect compared to the full irrigation on tomato physiological indexes during non-critical growth periods(e.g.seedling or fruit expanding period).Water stress enhanced tomato quality but inevitably reduced its yield during each growth stage.The application of mild water stress during the fruit expanding stage(W1F)seemed to be the best treatment to provide satisfactory fruit quality and yield based on RSR.