Dynamics And Distribution Of "Candidatus Liberibacter Asiaticus" In Citrus Roots And Its Effect On Arbuscular Mycorrhizal

Citrus Huanglongbing(HLB)is one of the most destructive.Guangdong,where the HLB was first found,was one of the biggest citrus production area in China,Citrus Shatangju(Citrus reticulata cv Shatangju),one of most popular commercial citrus cultivars in Guangdong province,was affected by HLB with the large economic losses.Previously study showed that the pomelo(Citrus maxima Burm.)can have longer survival time than others citrus cultivars after affected with HLB.However,the distribution of HLB-associated pathogen(“Candidatus Liberibacter asiaticus”,CLas)was still known.Currently,the change of roots of Shatangju and pomelo after affected with HLB are rarely reported.After affected with HLB,the citrus root was destructively damaged,which led to a limited growth of citrus.Therefore,research on HLB-affected citrus root could reveal the pathogenesis of HLB-host interaction and provide new insights for HLB control.In this study,the real-time PCR was applied to monitor the annual dynamic changes of the CLas in the root and leaf of HLB-affected citrus Shatangju and pomelo and further revealed the fluctuation pattern of CLas.By comparing and analyzing the concentration of CLas in root and leaf of citrus Shatangju to show the distribution of CLas.By comparing infection rate of the mycorrhizal mycorrhizal fungi in healthy citrus,citrus with only leaf infected by CLas,citrus with both leaf and root infected by CLas to reveal the influence of mycorrhizal fungi in citrus root by CLas infection.The main results are shown as follow:1.The combination analysis of the dynamic of CLas and symptom development in citrus Shatangju and pomelo revealed that more severe symptom was showed with higher concentration of CLas.With the infection of CLas in root,most of fibrous roots were loss and the development of root was nearly stopped in both citrus Shatangju and pomelo.In addition,the leaves and fruit severely drop out and the growth of tree declineed rapidly.However,compared with pomelo,more rapidly decline and losses of fibre were obaserved in citrus Shtangju,indicated the pomelo could be more resistant of HLB than citrus Shatangju.2.The concentration of CLas in leaf was higher than root in both citrus Shatangju.The highest concentration of CLas in both leaves and roots was observed in the in autumn,while the lowest concentration was observed in summer.The concentration of CLas in leaves was rapidly increased during October and December and higher than it detected in other months.The concentration of CLas in root was significantly higher in November than others.3.Dynamic analysis of CLas revealed the CLas concentration in leaf was always higher than it in root of pomelo.The change of CLas concentration in leaves and root was opposite.The CLas concentration in leaves was higher in spring and winter but lower in summer and autumn.However,the CLas concentration in root was higher in summer and autumn but higher in spring and winter.The highest CLas concentration in leaves was observed in winter,while highest CLas concentration of root was observed in autumn.4.Comparison of the dynamic change of CLas concentration in both leaves and roots of in citrus shatangju and pomelo revealed that CLas concentration of leaf and root in pomelo was significantly higher than those in citrus Shatangju,i.e.pomelo’s leaf > citrus shatangju’s leaf > pomelo’s root > citrus shatangju’s root.The change tendency of CLas concentration was different in citrus Shatangju and pomelo.5.Comparison of CLas concentration in roots and leaves located in different position in citrus shatangju revealed the CLas concentration of all leaves was significantly higher than that it in roots.The CLas concentration in roots and leaves from the same side was uneven.In addition,the distribution of CLas concentration and loss of fibrous root was also uneven.The distribution of roots bacteria content was uneven,and the loss of the However,the CLas concentration in leaves was opposite as the number of fibrous root,i.e.the higher concentration of CLas led to the less fibrous roots in the same orientation.6.Comparison of the infection rate of mycorrhizal fungi among the healthy citrus,citrus with only leaf infected by CLas,citrus with both leaf and root infected by CLas showed that no significant difference between healthy citrus and citrus with only leaf infected by CLas,but both of them was higher that citrus with both leaf and root infected by CLas.This result indicated that the CLas could suppression the infection of mycorrhizal fungi to citrus root.