Evaluation Of Shadetolerance Of Sweet Potato And Its Physiological Response To Low Light

This paper seeks for a reasonable evaluation method of shade tolerance of sweet potato,the cultivars were selected with strong shade-tolerance,and studied the physiological response of sweet potato of different shade tolerance to low light,thus provide theoretical support for the cultivation of high quality and yield sweet potato.This study used the method of artificial shade,simulated the model of sweet potato/maize relay-intercropping,according to the difference of physiological and biochemical variation law,agronomic traits and yield traits of sweet potato at tuber root bulking stage under the different shading levels,29 different sweet potato cultivars?lines?were evaluated about the shadow resistance by different index of shade-tolerance coefficient,and compared different evaluation methods;We measured and analyzed agronomic traits,photosynthetic characteristics,stress physiology and yield and quality indexes of five sweet potato cultivars?lines?with different shade tolerance.The results are as follows:1 shade-tolerance coefficient of single index and correlation analysisThis study showed that the variation law of different cultivars?lines?that the shade-tolerance coefficient of the same single index is different with shading treatment,the variation law of the same cultivars?lines?that the shade-tolerance coefficient of different single index is different with shading treatment,The variation coefficients of stomatal conductance?Gs?,net photosynthetic rate?Pn?,non-photochemical quenching coefficient?NPQ?and transpiration rate?Tr?were large,which were 69.07%,67.55%,61.91%and49.99%,respectively.The variation coefficients of stem weight,vine length,leaf area index?LAI?and branch number were medium,which were 28.70%,24.90%,24.84%and24.13%,respectively.Except intercellular carbon dioxide concentration?Ci?,each single index is significant or very significant correlation with one or more single index,among which branch number,internode number,stem weight,Pn,Tr,actual quantum yield of PSII(?_PSII)and NPQ are all correlated with four other indexes.It can be seen that shading treatment has a great influence on Gs,Pn,NPQ,Tr,stem weight,vine length,LAI and branch number of sweet potato,and the correlation between different indexes is large.2 different shadow resistance evaluation result and comparisonThe results were different by the different evaluation ways,the same caltivar?line?belonged to different category with different ways.Analyzed reduction of average yield of all cultivars?lines?,the results showed that the?and?classes was no significant difference classes with the evaluation index of the Pn;Stem dry weight as evaluation index,reduction of average yield of the?class significantly lower than the?and?classes;NPQ as evaluation index,reduction of average yield of the?class significantly lower than the?class,and there was no significance between the?class and the?class;There were greatly significant difference among different classes with the evaluation of comprehensive index,reduction of average yield of the?class significantly lower than the?and the?classes,and the?class was significantly lower than the?class.It can be seen that the evaluation result of single index is inconsistent with variation of yield reduction,while the evaluation result of comprehensive index is corresponding to the variation of yield reduction,it indicated that the analysis result of shade tolerance is more reliable with comprehensive index.3 sweet potato response to weak light stressShading increased plant height and internode number of different sweet potato cultivars,other index of agronomic traits reduced;After regaining normal light,stem diameter of the strong shade-tolerance cultivar yushu17 that decreased significantly,branch number,vine length and internode number increased under shading than control treatment,moderate shade-tolerance cultivars leaf area index?LAI?,fresh weight of leaves and stem were higher with shading treatment than the control,all agronomic trait indexes of shade-intolerance cultivar qianshu no.8 lower with shading treatment than control.Under the shading treatment,the root length,root surface area,root volume and average diameter of sweet potato were significantly lower than control treatment,and the minimum reduction of root length,root surface area and root volume were yushu17?15.36%,0.71%and 16.67%,respectively?.The maximum reduction of root length and root surface area were yuzishu no.2?52.21%and 52.66%,respectively?.while the largest reduction of root volume was qianshu no.8?55.32%?.In terms of average diameter,except for yushu15,the cultivar with the smallest reduction was yushu198,and the cultivar with the largest reduction was qianshu no.8?10.17%and 20.59%,respectively?.The contents of chlorophyll a,chlorophyll b and total chlorophyll were significantly higher in leaves of all varieties under shading treatment than control treatment,while the chlorophyll a:b was significantly lower than control treatment.The higher the shade tolerance,the greater the increase of chlorophyll content.Compared with the shading stage,the increase of strong shade-tolerance and moderate shade-tolerance cultivars generally were lesser than shade-intolerance after regaining normal light.During the shading stage,the content of carotenoid was significantly higher than that the control treatment in leaves of yushu17 and yushu15,while other cultivars were lower than the control treatment.After regaining normal light,except for yushu15,which showed significantly lower shade treatment than the control treatment,other cultivars showed higher in shade treatment than the control treatment,and the only significant difference was qianshu no.8.During the shading stage,Pn and Gs of different cultivars was significantly lower than control treatment,while Ci and Tr were opposite.After regaining normal light,the photosynthetic characteristic indexes of shade tolerant cultivars yushu17 were higher than the control treatment,Pn and Gs of the difference between the shading treatment and the control treatment was reduced,and the Pn and Tr of shade tolerant cultivars qianshu no.8 were higher than the control treatment,but the difference was not significant.Shading decreased The activity of photosynthesis-related enzymes in sweet potato,and RuBP carboxylase activity and SPS activity were significantly lower than control treatment during shading and after regaining normal light.During the shading period,the strong shade-tolerance cultivar yushu 17,which the decrease of sucrose phosphoric acid synthase?SPS?activity was the lowest in leaves,and shade-intolerance cultivar qianshu no.8 was the largest.After regaining normal light,the variety with the smallest reduction in shading treatment compared with the control treatment was yuzishu no.2,followed by yushu17,and the variety with the largest reduction was qianshu no.8.In addition,RuBP carboxylase activity of leaves of yushu17 decreased the least after regaining normal light.During shading stage,shading decreased the activities of superoxide dismutase?SOD?and catalase?CAT?in the leaves of all sweet potato cultivars,while the content of proline?Pro?increased,but the content of malondialdehyde?MDA?varied among different varieties in leaves.After regaining normal light,the Pro content of sweet potato leaves was higher than the control treatment,and the CAT activity was lower than the control treatment.The MDA content was significantly higher under shading than the control in the leaves of shade-intolerance cultivar qianshu no.8,but the strong shade-tolerance cultivars yushu17 was opposite.The results showed that the yield of all varieties were lower under shade condition than the control treatment by analyzing yield and quality,among which the cultivars yushu17 and qianshu no.8 reduced by 11.28%and 52.62%respectively.Under the shade treatment,the dry matter content and soluble sugar content of sweet potato tuber root were lower than the control treatment on the whole,but the soluble protein content of sweet potato was significantly higher than the control treatment.In summary,sweet potato can adjust plant morphology by reducing root length andvolume,reducing branch number and increasing vine length and internode number to adapt to the low-light environment,enhance photosynthetic capacity by increasing photosynthetic pigment content in leaves,and protect membrane system by increasing the Pro content of leaves.Compared with the cultivars with shade-intolerance,the cultivars with strong shade tolerance were less affected by weak light in plant morphological development,photosynthetic physiological response and membrane system protection,and had greater advantages in restoring normal morphology and improving photosynthetic capacity after regaining normal light.