New insights in phytoplasma-vector interaction: acquisition and inoculation of Flavescence dorée phytoplasma by Scaphoideus titanus adults in a short window of time

The leafhopper Scaphoideus titanus is able to transmit 16SrV phytoplasmas agents of grapevine’s Flavescence dorée (FD) within 30-45 days, following an Acquisition Access Period (AAP) of a few days feeding on infected plants as a nymph, a Latency Period (LP) of 3-5 weeks becoming meanwhile an adult, and an Inoculation Access Period (IAP) of a few days on healthy plants. However, several aspects of FD epidemiology suggest how the whole transmission process may take less time, and may be start directly with adults of the insect vector. Transmission experiments have been set up under lab condition. Phytoplasma-free S. titanus adults were placed on broad bean (BB) plants (Vicia faba) infected by FD-C (16SrV-C) phytoplasmas for an AAP=7 days. Afterwards, they were immediately moved onto healthy BB for IAP, which were changed every 7 days, obtaining three timings of inoculation: IAP 1, IAP 2 and IAP 3, lasting 7, 14 and 21 days from the end of AAP, respectively. DNA was extracted from plants and insects, and PCR were performed to identify FD phytoplasmas. Insects were dissected and fluorescent in situ hybridization was made to detect the presence of phytoplasmas in midguts and salivary glands. The rate of infection in insects ranged 46-68% without significant differences among IAPs. Inoculation in plants succeeded in all IAPs, at a rate of 16-23% (no significant differences). Phytoplasma load was significantly higher in IAP3 than IAP 1-2 for both plants and insects.