Use of Cryotherapy to Eradicate Pathogens from Horticultural Crops

Cryotherapy is method by which pathogens are eliminated from infected plant materials through the process of cryopreserving and then recovering shoot tips. It has been successfully implemented in potato, sweet potato, grapevine, raspberry, Prunus, and other fruit crops to eliminate pathogens that have been difficult to clean-up using traditional methods. Candidatus Liberibacter asiaticus (Las), the bacterium associated with huanglongbing (HLB), has been eliminated from Citrus using cryotherapy methods.  The success of cryotherapy depends on having only cells that do not host pathogens survive the exposure to liquid nitrogen. Meristems up to 1 mm long (including about three leaf primordia) are excised, in contrast to the meristem with one leaf primordium (about 0.1 mm long) in traditional shoot tip grafting. Use of larger shoot tips increases the survival rate and makes the procedures more reproducible.  Application of cryotherapy for eradication of other Citrus diseases such as viroids and Citrus tatterleaf capillovirus may provide a better alternative than traditional shoot tip grafting methods.