There are a variety of symptoms, which vary according to host.
Grape: Symptoms of the grapevine yellows disease can be observed in leaves, tendrils, and fruiting clusters. Leaves of white grape varieties tend to become yellowed and may have veinal necrosis, as well as downward curling of the leaf margins. Unlike some other grapevine diseases, the grapevine yellows diseases are characterized by shriveling/abortion/necrosis of fruiting clusters.
Solanaceous Hosts: In potato, upward rolling and purpling of the leaves were observed. The symptoms appeared similar to those of "zebra chip", a disorder of potato recently found to be associated with "Candidatus Liberibacter solanacearum" in New Zealand and the United States. In Jerusalem cherry (Solanum pseudocapsicum), symptoms include: witches" broom, foliar yellowing, and reduced leaf size.
See Grape or Solanaceous Commodity-based Survey Reference or the S&T Pest Datasheet for descriptions of symptoms by host.