Interactions between citrus exocortis and potato spindle tuber viroids in plants of Gynura aurantiaca and Lycopersicon esculentum.

Abstract

Plants of Gynura aurantiaca and tomato (Lycopersicon esculentum) were inoculated with severe strains of citrus exocortis viroid (CEV) and potato spindle tuber viroid (PSTV). The progeny of both viroids was analyzed by two systems of PAGE which allowed discrimination between CEV and PSTV on the basis of their different sizes. When inoculated separately to G. aurantiaca CEV and PSTV induced severe and very mild symptoms, respectively, with CEV accumulating to a higher level than PSTV, whereas when tomato was the host, each viroid induced severe symptoms (although the reaction caused by PSTV was more intense) with PSTV reaching a higher steady-state concentration than CEV. The simultaneous inoculation of both viroids induced in G. aurantiaca the characteristic symptomatology of CEV, which was the only viroid that could be detected, whereas the response observed in tomato was that typical of PSTV, and only this viroid could be recovered. On the other hand, when G. aurantiaca plants were first inoculated with PSTV and later challenged with CEV, part of the plants displayed the characteristic severe reaction of CEV and both viroids were present in the corresponding extracts, but the other part showed the mild symptomatology induced by PSTV, and only this viroid could be isolated. However, when the protected plants were topped the new shoots exhibited severe symptoms and only CEV could be detected. These results suggest that CEV and PSTV compete for a limiting host factor needed for their replication, transport or accumulation, with CEV and PSTV having the highest affinity for the G. aurantiaca and tomato factors, respectively.