Citrus tristeza virus transmission by the Toxoptera citricida vector: in vitro acquisition and transmission and infectivity immunoneutralization experiments.

Citrus tristeza virus (CTV) is transmitted by several aphid species in a semi-persistent manner with Toxoptera citricida, the brown citrus aphid (BrCA), being the most efficient. As yet, the molecular interactions between the virus and its aphid vectors have not been determined. This is the first report of aphids acquiring CTV from preparations through an artificial membrane and then transmitting it to receptor plants. The BrCA fed across artificial membranes on crude tissue preparations made from CTV-infected bark tissue were able to transmit CTV to virus-free receptor plants at low rates. CTV p20, p27 and p25 proteins, detected by Western blots, were present in all crude tissue preparations from CTV-infected plants. Partially purified CTV preparations were not transmitted by the BrCA in this manner. Infectivity immunoneutralization experiments were conducted where aphids were forced to feed in vitro on three CTV-specific antibodies (p25, p27 and p20) before being placed on receptor plants following a 48h acquisition feed on CTV-infected source plants. There were no differences in transmission rates among the majority of treatments and the control treatments. However, in one infectivity immunoneutralization experiment, the CTV p20 antibodies significantly enhanced CTV transmission compared to buffer only, pre-immune antiserum or no antibody control treatments. This suggests the inactivity of CTV p20 aids BrCA transmission of virions.