A protocol for successful transmission of ‘Candidatus Liberibacter asiaticus’ from citrus to citrus using Diaphorina citri
A protocol to successfully transmit the huanglongbing (HLB) pathogen, ‘Candidatus Liberibacter asiaticus’ (Las), from citrus-to-citrus plants using the Asian citrus psyllid (ACP), and an alternative way to help growers control ACP are proposed. Best results were obtained when pathogen acquisition by adults reared on fully symptomatic Las-positive plants, latency, and inoculation, occurred at ambient air temperatures ranging from 24 to 28°C, and by confining single infective adult ACP for seven days on soft newly developing vegetative shoots (stages v2 to v4). No infection resulted from confinement of infective ACP adults on mature leaves (stage v6). Under the described conditions, single ACP adults could successfully transmit Las to an average of 56.5% (35 to 83%) of plantlets with v2 to v4 shoots growing in 0.3 L tubes, and to 80.5% (76 to 86%) of plants with v2 to v4 shoots growing in 4.7 L pots. The use of single insects and plantlets reduces labor, space and other resources required to undertake transmission tests. It also reduces time required for transmission studies and should help accelerate research on HLB. The results were used to develop an index for favorability to infection (IFI) to determine orchard vulnerabilities to Las. The IFI is based on the heterogeneous population of new shoots that occurs on tree canopies and may offer alternative or complementary alternatives to the laborious and costly insect surveys currently used in most instances to determine threshold levels for insecticide applications.