EFFECTS OF FEEDING SUBSTRATE ON RETENTION AND TRANSMISSION OF XYLELLA FASTIDIOSA STRAINS BY THE GLASSY-WINGED SHARPSHOOTER

• Author(s): Cooksey, Donald; Costa, Heather; Perring, Thomas;
• Abstract: This is a continuation of our three year project designed to study the effect of feeding substrate on the acquisition and retention of Xylella fastidiosa (Xf) by the glassy-winged sharpshooter (GWSS), Homalodisca coagulata. We are using two strains of Xf that are present in California: a Pierces disease (PD) strain that infects grape, and an oleander leaf scorch (OLS) strain that infects oleander. Last year we reported that GWSS that acquired the PD strain from grape or the OLS strain from oleander and subsequently confined to chrysanthemum (a non-Xf host), retained the bacterium at least seven days after exclusive feeding on the non-host. Thus, Xf in the GWSS foregut does not need continual access to host plant xylem. Secondly, we reported that GWSS transmitted PD and OLS strains when they acquired the bacteria from a plant, but they did not transmit either strain when media-grown bacteria were delivered through the cut-stem system. This result forces us to use whole plants as our bacterial source in transmission experiments. This past year, we focused on objectives 3-5. Studies showed that GWSS given access to PD, followed by OLS, retained both PD and OLS and transmitted PD at a higher rate than OLS. When GWSS were given access to OLS followed by PD, they retained PD at a much higher rate than OLS and transmission to plants was poor. Results suggest that PD may have become established in the foregut better than OLS or that it out-competed the OLS strain. Further analyses showed that sharpshooters which tested positive for only the OLS strain had a higher percentage inoculation rate of the PD strain. Possible explanations for these results are provided. For objective 4, we found that antibiotics effectively killed Xf in the GWSS foregut by treating either before or after bacterial acquisition. In our last objective, there was no difference in survival of PD at pH ranging from 4.5 to 9.8. This past year, we focused on objectives 3-5. Studies showed that GWSS given access to PD, followed by OLS, retained both PD and OLS and transmitted PD at a higher rate than OLS. When GWSS were given access to OLS followed by PD, they retained PD at a much higher rate than OLS and transmission to plants was poor. Results suggest that PD may have become established in the foregut better than OLS or that it out-competed the OLS strain. Further analyses showed that sharpshooters which tested positive for only the OLS strain had a higher percentage inoculation rate of the PD strain. Possible explanations for these results are provided. For objective 4, we found that antibiotics effectively killed X. fastidiosa in the GWSS foregut by treating either before or after bacterial acquisition. In our last objective, there was no difference in survival of PD at pH ranging from 4.5 to 9.8.
• Publication Date: Dec 2005
• Journal: 2005 Pierce's Disease Research Symposium