Displacement of tomato yellow leaf curl virus (TYLCV)-Sr by TYLCV-Is in tomato epidemics in spain

A progressive displacement of tomato yellow leaf curl virus (TYLCV)-Sr by T YLCV-Is was observed in tomato epidemics in southern Spain based on inciden ce data of both virus species obtained during surveys conducted between 199 6 and 1998. Ecological factors that might be involved in such a displacemen t, such as competition of TYLCV-Sr and TYLCV-Is in tomato, transmission by local biotypes (B and Q) of Bemisia tabaci, and presence in weeds and alter nate crops, have been analyzed. No selective advantage is observed for TYLC V-Sr or TYLCV-Is in tomato plants either infected via Agrobacterium tumefac iens or via B. tabaci. However, TYLCV-Is is more efficiently vectored by lo cal biotypes of B, tabaci; and common bean, a bridge crop between tomato cr ops, is a host for TYLCV-Is but not TYLCV-Sr. Therefore, common bean acts a s a reservoir for TYLCV-Is. These two factors are probably responsible for the displacement of TYLCV-Sr by TYLCV-Is as the causative agent of epidemic s in tomato in southern Spain.