Progress in study of screening mild strains of Citrus tristeza virus

Tristeza caused by Citrus tristeza virus(CTV)has resulted in devastating losses in global citrusproduction. At present, the most effective mean to protect commercial citrus against endemic stem pittingisolates of CTV is cross protection with appropriate mild CTV isolates. CTV exists as a large number ofdistinct strains differing in biological characters in citrus. In this paper,progress in studies of the screen-ing of mild strains of CTV was reviewed. Furthermore, the possible mechanisms and disadvantages for us-ing cross protection against CTV were also discussed in order to lay a sound foundation for better controlof the damage caused by CTV.