**3.4** *Citrus gummy bark viroid* **(CGBVd)** *or Citrus viroid II*

This viroid is a strain of *Hop stunt viroid* and so it places in *Hostuviroid* genus [55]. This viroid infects the sweet orange tree and causes spots or a line of reddish-brown, gum-impregnated tissue around the scion circumference especially visible near the bud union. In a severe infection, discoloration and gumming are extended and maybe to reach the main branches [39, 40, 55]. For the first time, this disease with discoloration phloem by Nour-Eldin in Egypt [39, 40]. After that, this disease is recorded in many countries such as North African and Near East countries including Saudi Arabia, Sudan, Lybia, Iran, Turkey, and Greece [40].

If this viroid infects Dortyol and Washington navel trees, they show bark scaling resembling mild psorosis scaling. It is suggested that a variant of CVd-I1 may be either the causal agent or a factor involved in gummy bark symptoms [40].
