Latency and incubation of ‘Candidatus Liberibacter asiaticus’ in citrus after vector inoculation

Abstract

Huanglongbing (HLB) is a bacterial disease of citrus, transmitted by the Asian citrus psyllid Diaphorina citri. In Brazil, the disease is managed by insecticide spray targeting vector control and removal of trees when they first show HLB symptoms that aims to reduce ‘Candidatus Liberibacter asiaticus’ (CLas) inoculum within the orchard. Albeit symptoms of HLB in field trees appear only months or years after the initial infection, the shortest incubation period (time between pathogen infection and symptom expression) reported for CLas in citrus was about 4 months after inoculation in studies in which this pathogen was graft-inoculated. In this work, an incubation period of 80 days (2.5 months) was recorded for citrus seedlings and 5 months for citrus nursery plants after inoculation with the psyllid vector itself. Psyllids were capable of acquire CLas from the infected seedlings and nursery plants 2.5 months after inoculation. These results show that the latency of CLas in planta is shorter than the incubation. Assessment of the presence of liberibacter in psyllids could be used as a proxy for the presence of HLB bacterium in presymptomatic stage of the plants.