2013 Annual Report
Promising USDA scion selections exposed to Candidatus Liberibacter asiaticus, causal organism of Huanglongbing disease are at risk of being lost due to the disease. Because citrus is a clonally propagated crop and many genotypes do not come true from seed, it is necessary to maintain the germplasm as whole plants, an expensive and vulnerable endeavor. Cryopreservation (maintaining live biological material at liquid nitrogen temperature) has been used with other clonally propagated crops and holds promise for citrus. In addition to preservation, cryotherapy may be a means to eliminate not only Candidatus Liberibacter asiaticus, but also other graft transmissible pathogens. ARS scientists in Ft. Pierce, Riverside, and Ft. Collins are collaborating to establish a cryotherapy and preservation protocol for citrus. Prior to the cryotherapy treatment it was essential to have plant material in enough abundance, at the proper stage of growth and as sanitary as possible to ensure success. At Ft. Pierce, promising citrus scion hybrids were identified and propagated, and are being maintained in the greenhouse to provide the budwood needed for cryotherapy. Trees are tested using standard molecular biology protocols for Candidatus Liberibacter asiaticus and citrus tristeza virus. Budwood was provided to the Germplasm Preservation Laboratory in Ft. Collins where it undergoes cryotherapy and preservation. During this reporting period, experiments have been conducted at Ft. Pierce to determine the efficacy of treating budwood with either heat or antibiotics prior to budding with the objective of eliminating Candidatus Liberibacter asiaticus. Treatments have been completed, buds grafted onto rootstocks and trees are being maintained in the greenhouse for pathogen testing.