土壤湿度对番茄青枯病侵染进程和光合特性及根系生长的影响

Effects of soil moisture on infection process,photosynthetic characteristics and root growth of tomato plants with bacterial wilt

【目的】探究不同土壤湿度下接种青枯菌对番茄植株发病情况、细菌侵染进程、植株光合作用和根系生长的影响,为番茄青枯病的防治提供参考。【方法】以易感青枯病番茄品种金鹏14-8和青枯菌菌株P380为材料,设置4个土壤湿度(用土壤相对含水量表示)水平,分别为高湿T1(85%~100%)、中湿T2(70%~85%)、低湿T3(55%~70%)、干旱T4(40%~55%),对每个土壤湿度处理的番茄植株进行接种青枯菌和不接种青枯菌(对照)处理,监测不同土壤湿度条件下植株的发病率和病情指数,采用扫描电子显微镜观察青枯菌在番茄茎中的侵染进程及其数量分布,并对接种和未接种青枯菌(对照)植株的光合作用指标及根系形态指标进行比较分析。【结果】接种青枯菌后第3天,T1、T2、T3处理的番茄植株开始出现青枯病患病症状,T4处理未出现患病症状,随着接种时间的推移,T1处理番茄植株的发病率和病情指数增加迅速,接种后第11天其发病率高达96.67%,植株几乎全部发病;T2处理增加较快,接种后第11天发病率达57.67%;T3和T4处理增加极其缓慢,接种后第11天发病率和病情指数分别为21.67%,13.92和10.00%,5.92。扫描电镜观察结果表明,同一高度茎段中青枯菌数量随着植株土壤湿度的降低而下降,各土壤湿度处理间茎下段(SL1)和茎中段(SL2)青枯菌数量变化规律相同,即T1处理青枯菌数量显著高于T2、T3、T4处理,但T2、T3、T4处理间青枯菌数量差异不大;各处理茎上端(SL3)青枯菌数量差异总体不显著。相同土壤湿度下青枯菌数量在植株茎高度方向上呈下降趋势,即SL1>SL2>SL3。与未接种(对照)植株相比,接种青枯菌后第4天,各土壤湿度处理番茄植株P n、T r、G s和C i均降低,各指标值均随土壤湿度降低而下降;接种青枯菌后第6天,各处理番茄植株的总根系长度、总根表面积、总根系体积均降低,根尖数增加,根平均直径变化不明显,总根系长度、总根表面积和根尖数均表现为T1>T2>T3>T4的规律,总根系体积大小表现为T1>T2>T4>T3。【结论】降低土壤湿度可以抑制番茄青枯病的发生,减缓细菌在植株茎中的侵染进程,使植株茎秆木质部中青枯菌的定殖数量降低;青枯菌侵染导致番茄植株的光合作用和根系生长受到抑制。

【Objective】This study explored the effects of inoculating Ralstonia solanacearum under di-fferent soil moistures on disease conditions,bacterial infection process,plant photosynthesis and root growth of tomato plants to provide reference for the control of tomato bacterial wilt.【Method】Susceptible tomato cultivar of Jinpeng 14-8 and R.solanacearum strain P380 were selected in this study with four soil moisture levels(expressed by soil relative water content)of high soil moisture T1(85%―100%),middle soil moisture T2(70%―85%),low soil moisture T3(55%―70%)and drought T4(40%―55%).Plants were inoculated with or without R.solanacearum(control)and incidence and disease index of plants in different soil moisture treatments were monitored.The infection process and quantity distribution of R.solanacearum in tomato stem were observed by scanning electron microscope(SEM).Photosynthetic indexes and root morphology indexes of inoculated and uninoculated plants were also compared and analyzed.【Result】Three days post inoculation(dpi),tomato plants in T1,T2 and T3 began to show symptoms of bacterial wilt,while T4 showed no symptoms.Over time,the incidence and disease index of tomato plants in T1 increased rapidly,and the incidence rate reached 96.67%at 11 dpi.The incidence rate of T2 was 57.67%at 11 dpi.T3 and T4 increased slowly with incidence and disease index of 21.67%and 13.92 for T3 and 10.00%and 5.92 for T4 at 11 dpi.The results of SEM showed that the number of R.solanacearum at same stem segment heights decreased with the decrease of soil moisture.The lower segment of stem(SL1)and middle segment of stem(SL2)showed same trends that T1 had significantly higher number than T2,T3 and T4.There was no significant difference between T2,T3 and T4.The upper stem segment(SL3)had little difference between four treatments in general.With same soil moistures,the number of R.solanacearum was in the decreasing order of SL1>SL2>SL3.Compared with uninoculated plants,P n,T r,G s and C i of tomato plants decreased in all treatments at 4 dpi,and they decreased with the decrease of soil moisture.The total root length,total root surface area and total root volume of tomato plants in all treatments decreased,the root tip number increased,and the average root diameter did not change significantly at 6 dpi.The total root length,total root surface area and root tip number were in the order of T1>T2>T3>T4,while the total root volume was in the order of T1>T2>T4>T3.【Conclusion】Reducing soil moisture inhibited the occurrence of tomato bacterial wilt,slowed down the infection process in plant stem,and reduced the amount of bacteria colonization in xylem.Photosynthesis and root growth of tomato plants were also inhibited by R.solanacearum infection.