What is an example of a xylem-limited fastidious bacterium?

Xylella fastidiosa is indeed an example of a xylem-limited fastidious bacterium. This bacterium is known for its association with various plant diseases and its unique lifestyle, as it resides primarily within the xylem tissue of plants. Being xylem-limited means that it specifically targets the xylem vessels where it can block water transport, leading to symptoms such as wilting, leaf scorch, and eventually plant death. The term "fastidious" refers to the bacterium's requirement for specific growth conditions, making it difficult to culture in a laboratory setting. This characteristic further emphasizes its dependence on the plant host for survival and reproduction.

Other choices include various bacteria and pathogens linked to plant diseases, but they do not share the same specific characteristics of being fastidious and xylem-limited. For instance, Xanthomonas species are known for infecting a variety of plant tissues, Agrobacterium primarily affects plant cells via genetic transformation, and Phytoplasma, while also dependent on plant hosts, is not classified as a bacterium in the traditional sense and has different pathogenic characteristics.