Analysis of an in vivo generated mutant that is not transmissible by Bemisia tabaci.

A cloned DNA obtained from TYLCV-infected tomato plants from Sicily was unable to infect plants efficiently by agroinoculation. Only about 5% of the challenged plants developed wild-type infection, with typical symptoms and all viral DNA forms as the field infected plants. From one of these plants, however, the disease could not be transmitted to new tomato plants by the natura1 vector Bemisia tabaci. We have further analysed this mutant and recloned viral DNA. Sequence analysis of the coat protein gene showed a point mutation inducing a Q to H change at aminoacid 134. Sequence comparison arnong whitefly-transmitted geminiviruses showed always a neutra1 polar aminoacid (S, N, T or Q) at this position. In order to test the hypothesis that a H at this position is sufficient to impair acquisition or transmission by the vector, while maintaining the capability of TYLCV to assemble virus particles and to infect plants systernically, we have mutated the coat protein of a well transmissible isolate of the virus. Tomato plants have then been agroinoculated with this mutant. Data will be presented on the transmissibility of it by whiteflies.