Ultrastructural Host Cell Changes Associated With Tomato Yellow Mosaic

Abstract

Leaf phloem cells of tomato [Lycopersicon esculentum] and Nicotiana glutinosa plants affected by tomato yellow mosaic (mosaico amarillo del tomate [MAT]) showed striking changes in nuclear morphology 6 days after inoculation either mechanically or by infectious whiteflies [Bemisia tabaci]. The main changes were hypertrophy of the nucleus, which contained large masses of viruslike particles (18-20 nm in diameter) and often fibrillar rings were observed. The viruslike particles were observed as large masses in the nuclei of infected phloem cells of both hosts. In N. glutinosa they also occurred in the nuclei of mesophyll cells. Occasionally fibrillar rings were found in the nuclei of epidermal cells of N. glutinosa but not in tomato. Comparable tissues from healthy plants were free of nucleopathy. The symptoms and signs of MAT resemble those reported for other whitefly-transmitted viruses such as bean golden mosaic virus and euphorbia mosaic virus.