1a.Objectives (from AD-416):
The objective of this cooperative research is identify methods for increasing tolerance to liquid nitrogen temperatures in avocado and Citrus crops and to determine if pathogens are eliminated during the cryopreservation process.
1b.Approach (from AD-416):
Avocado and Citrus genetic resources will be obtained from the National Plant Germplasm System Repositories in Miami, FL and Riverside, CA, respectively. In vitro cultures will be established and propagated to serve as rootstocks for cryopreserved shoot tips. Cryoprotectant and liquid nitrogen exposure tests will be performed using shoot tips excised from field-grown budwood. Cryopreservation experiments will be performed using disease infected and clean plant materials to determine if liquid nitrogen exposure eradicates diseases from infected tissues.
We have worked to develop cryopreservation protocols for avocado and Citrus. The Citrus research has been highly productive, resulting in a publication (in press) and increased industry interest. Shoot tip survival rates after liquid nitrogen exposure have now reached 70%. We have begun cryopreserving key lines of Citrus that are critical to both the USDA National Plant Germplasm System and the California Citrus Industry using the methods that have been developed. We have now begun cryotherapy research, in collaboration with USDA-ARS-Riverside, to determine if viruses and viroids can be removed from contaminated materials as a result of the cryopreservation process (cryotherapy). Results of these projects were presented in two presentations at the American Society for Horticultural Science Annual Conference in Miami, FL , July 2012. We have also performed a thorough investigation of in vitro introduction and propagation of avocado genetic resources. We have successfully introduced excised embryos into tissue culture and propagated them in vitro. We have not yet identified tissue culture methods to successfully and reliably regenerate healthy plants from excised shoot tips from in vitro or greenhouse plants, thus limiting our ability to develop cryopreservation methods for avocado at this time.