Quantification and ecological study of ‘Candidatus Liberibacter asiaticus’ in citrus hosts, rootstocks and the Asian citrus psyllid

Using proper managements for Citrus Huanglongbing (HLB), which caused by Candidatus Liberibacter asiaticus (Las) and transmitted by Asian citrus psyllid (ACP) (Diaphorina citri), is a priority issue. The HLB control is based on healthy seedlings, tolerant rootstock cultivars and reduction of ACP population. We studied dynamic populations of Las in different citrus hosts and each instar of ACP and also examined the seasonal growth and distribution of Las in different tissues using conventional and TaqMan® real-time PCR. The results showed obvious symptoms and poor growth on hosts or rootstocks, indicating different levels of susceptibility/tolerance to HLB. Troyer citrange, Swingle citrumelo and woody apple are highly tolerant among 11 rootstock cultivars. Regarding distribution and seasonal analysis, mature and old leaves contained high concentrations of Las at cool temperatures in autumn and spring. For periodic detection, Las were detected earlier through psyllid-transmission than through graft-inoculation at 21 days post-infection, and the amounts of Las (AOL) varied in different hosts. Thus, different AOL (104-107 copy numbers/μL) and Las-carrying percentages (LCP) (40-53.3%) were observed in each citrus cultivar and on psyllids, respectively. Furthermore, both AOL and LCP were lower in nymphs than in adult psyllids, whereas the LCP on psyllids were not affected by the increasing acquisition-access time. The present study has significant implications for disease ecology. The combination of early detection, using proper rootstocks and constraining psyllid populations could achieve better management of HLB disease. This article is protected by copyright. All rights reserved.