Distribution of Candidatus Liberibacter asiaticus in individual navel orange tree

ObjectiveDistribution of Candidatus Liberibacter asiaticus(CLas) in Newhall navel orange tree was in-vestigeted, in order to provide reference for prevention and control of citrus Huanglongbing(HLB). MethodNewhall tree were used as research object, which had 1-3 branches with mottled yellow leaf symptoms. The leaves were collected from five main branches(A, B and C branches with mottled yellow leaves, D and E asymptomatic branches) on the trunk, re-spectively. Then samples were detected and analysed by using PCR and quantitative real-time PCR(qPCR), and CLas content in different parts of tree was analyzed by using 2-ΔΔCt method. For some branches with pathognomonic HLB-infected fruits but without symptomatic leaves, their fruits and leaves were detected, respectively. ResultThe results showed that, using PCR method, the positive rates of A, B, C, D, E were 88.57%, 61.11%, 54.17%, 6.67% and 0, re-spectively, while using qPCR method, the positive rates of A, B, C, D, E were 100.00%, 100.00%, 100.00%, 40.00%, 13.33% , respectively. Furthermore, 2-ΔΔCt analysis showed that, CLas content was higher in mottled yellow leaves than asymptomatic leaves, and the positive rate of infected fruits was higher than corresponding asymptomatic leaves. Conclu-sionContent and positive rate of CLas are higher in mottle yellow leaves and pathognomonic HLB-infected fruits than asymptomatic leaves, and CLas was distributed unevenly in the whole infected tree. In the detection, the samples with typi-cal symptoms or suspected samples should be selected, and then detected by qPCR method. Furthermore, once partial branchs of tree are found to be infected, the whole tree should be destroyed immediately.