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Title: Citrus cyopreservation: viability of diverse taxa and histological observations

Author
item Volk, Gayle
item Bonnart, Remi
item Shepherd, Ashley
item YIN, ZHENFANG - Sichuan University
item Lee, Richard
item Polek, Marylou
item Krueger, Robert

Submitted to: Plant Cell Tissue and Organ Culture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2016
Publication Date: 10/20/2016
Citation: Volk, G.M., Bonnart, R.M., Shepherd, A.N., Yin, Z., Lee, R.F., Polek, M., Krueger, R. 2016. Citrus cyopreservation: viability of diverse taxa and histological observations. Plant Cell Tissue and Organ Culture. doi:10.1007/211240-016-1112-4.

Interpretive Summary: Diverse citrus cultivars maintained clonally within gene banks serve as valuable resources for research and breeding programs worldwide. These critical collections are kept as trees within field, screenhouse, or greenhouse collections and are at risk of being lost due to unforeseen environmental or biological disasters. Cryopreservation technologies were used to process 150 Citrus accessions representing 32 taxa. Of those, 24 taxa had mean regrowth levels that were at least 40% after cryoexposure. The 36 navel orange (Citrus sinensis) accessions had an average regrowth level of 64%. There was no decrease in viability after three years of LN storage for the three accessions that are part of a long-term storage experiment. Histological observations revealed high levels of cell survival after LN exposure and cellular regrowth occurred between rootstock and shoot tips within two days of micrografting. We demonstrate that diverse citrus cultivars can be successfully cryopreserved within gene banks for long-term conservation and that this technology is ready to be implemented within the USDA-ARS National Plant Germplasm System.

Technical Abstract: Diverse citrus cultivars maintained clonally within gene banks serve as valuable resources for research and breeding programs worldwide. These critical collections are kept as trees within field, screenhouse, or greenhouse collections. These ex situ collections are at risk of being lost due to unforeseen environmental or biological disasters. Cryopreservation provides a secure method to back-up these important collections. Herein, we assessed the applicability of a vitrification-based cryopreservation method to conserve citrus collection cultivars. Shoot tips were excised from screenhouse-grown trees at the USDA-ARS National Clonal Germplasm Repository for Citrus and Dates. Shoot tips were then treated with cryoprotectants, plunged into liquid nitrogen (LN), warmed and then recovered by micrografting onto ‘Carrizo’ citrange seedling rootstocks. Of 150 cryopreserved Citrus accessions representing 32 taxa, 24 taxa had mean regrowth levels that were at least 40%. The 36 navel orange (Citrus sinensis) accessions had an average regrowth level of 64%. There was no decrease in viability after three years of LN storage for the three accessions that are part of a long-term storage experiment. Histological observations revealed high levels of cell survival after LN exposure and cellular regrowth occurred between rootstock and shoot tips within two days of micrografting. We demonstrate that diverse citrus cultivars can be successfully cryopreserved within gene banks for long-term conservation.