Conservation of U.S. Citrus Collections using Cryopreservation

The USDA–ARS National Plant Germplasm System and the University of California Citrus Variety Collection maintain more than 850 unique accessions of Citrus, Fortunella, and citrus wild species. We have developed a method to back-up critical screenhouse and greenhouse Citrus collections using cryopreservation. Shoot tips are excised from actively growing vegetative flushes, surface disinfected, and then treated with cryoprotectant solutions. Shoot tips are then immersed in liquid nitrogen, held, and warmed to check for survival. Recovered shoot tips are micrografted onto etiolated ‘Carrizo’ seedling rootstocks. Regrowth levels are greater than 50% for cultivars representing eight Citrus and Fortunella species. The method may also be useful for cryotherapy to remove pathogens from infected source plant material.