Optimization of in vitro germination and cryopreservation conditions for preserving date palm pollen in the USDA National Plant Germplasm System

Authors: ARAUJO DE OLIVEIRA, ANNIE - Federal University - Brazil; LEDO, ANA - Embrapa; Polek, Marylou; Krueger, Robert; Volk, Gayle

Submitted to: Plant Cell Tissue and Organ Culture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2020
Publication Date: 10/27/2020
Citation: Araujo De Oliveira, A., Ledo, A., Polek, M., Krueger, R., Volk, G.M. 2021. Optimization of in vitro germination and cryopreservation conditions for preserving date palm pollen in the USDA National Plant Germplasm System. Plant Cell Tissue and Organ Culture. 144:223-232. https://doi.org/10.1007/s11240-020-01907-1.
DOI: https://doi.org/10.1007/s11240-020-01907-1

Interpretive Summary: Date palm (Phoenix dactylifera L.) is a staple crop across arid and semi-arid regions around the world. The USDA-ARS National Plant Germplasm System maintains a date palm field collection at the University of California Coachella Valley Agricultural Research Station (UC-CVARS) in Thermal, CA. This collection includes male and female date palm trees. Research was performed to identify a method to cryopreserve pollen from the male date palm trees for long term preservation at the USDA-ARS National Laboratory for Genetic Resources Preservation in Fort Collins, Colorado. Both genebanks and date palm breeders benefit by having clearly defined methods for long-term pollen preservation in liquid nitrogen. Pollen was collected and the moisture content was adjusted. Pollen was kept at the moisture adjustment conditions for up to 56 days and then placed into liquid nitrogen vapor (LNV). Pollen viability was assessed for fresh, moisture-equilibrated, non-LNV and LNV-exposed pollen after up to 9 months. Pollen had in vitro germination levels of up to 47% and in vitro viability remained stable for pollen that was stored in LNV for 9 months. In addition, pollen also remained viable if it was cooled to and warmed from LNV for up to 60 cycles. These data suggest that long term storage in LNV can be used for date palm pollen preservation in genebanks.

Technical Abstract: Date palm (Phoenix dactylifera L.) is a staple crop across arid and semi-arid regions around the world. Both genebanks and date palm breeders benefit by having clearly defined methods for long-term pollen preservation in liquid nitrogen. Pollen was collected from the spathes of five date palm cultivars. The moisture content of the collected pollen was adjusted by placing samples over saturated salt solutions of Ca(NO3)2 and MgCl2 at 23 ºC or in a chamber set at 23% RH and 5 ºC. Pollen was kept at the moisture adjustment conditions for up to 56 days and then placed into liquid nitrogen vapor (LNV). Viability was assessed for fresh, moisture-equilibrated, non-LNV and LNV-exposed pollen after up to 9 months. Pollen had in vitro germination levels of up to 47% when it was rehydrated for 2h and then grown at 20 ºC on Marquard medium supplemented with 15% sucrose. In vitro viability remained stable for pollen that was stored in LNV for 9 months. In addition, pollen also remained viable if it was cooled to and warmed from LNV for up to 60 cycles. These data suggest that long term storage in LNV can be used for date palm pollen preservation in genebanks.