Long‐Term Preservation of Hop Pollen in Liquid Nitrogen1

Abstract

This research was initiated to evaluate long‐term hop (`Humulus lupulus`` L.) pollen storage for breeding purposes and germplasm preservation. Air‐dried pollen was stored in a refrigerator (3°C), a freezer (−18°C), and in liquid nitrogen (−196°C) and compared with fresh pollen by hand pollination of receptive female flowers and subsequent seed germination tests. Pollen stored in liquid N averaged four seeds per cone in test crosses over a 2‐year period as compared to slightly over five seeds per cone from fresh pollen. Pollen stored at −18°C lost about half of its viability after 1 year, while pollen stored at 3°C became nonfunctional within 1 year. Reducing moisture content of fresh pollen to about 10% prior to cold temperature storage was essential.