Effect of freezing and freeze-drying on the viability and storage of Lilium longiflorum L. and Zea mays L. pollen

The freeze-preservation of pollen is dependent on the interaction of several factors such as freezing rate, thawing rate, freeze-drying temperature and duration, storage temperature and environment and rehydration rates. Changes in any of these variables affects the others directly or indirectly.Rapid freezing of pollen at rates of approximately 200 °C/min maintains the highest degree of viable pollen in combination with rapid thawing rates of 218 °C/min. Rapid cooling and slow rewarming resulted in a substantial loss of pollen viability. This might indicate that intracellular ice crystals formed during rapid cooling perhaps grow into larger ice masses during slow rewarming or storage at temperatures above ?50 °C.The germinability of pollen freeze-dried at temperatures below ?50 °C was also prolonged over that of the controls. Germination values for unfrozen pollen stored for 30 days at 0–5 °C averaged 50% for lily and 20% for corn. Freeze-dried pollen stored for 30 days at the same temperature yielded considerably higher viability percentages for both lily and corn pollen. Drying time is an important factor, perhaps indicating that residual moisture is critical. Freeze-dried pollen can be stored at higher temperatures than frozen and control pollen. Freeze-dried material stored for five months at 0–5 °C, upon slow rehydration yielded intact grains which has average germination percentages of 25 for lily and 15 for corn. The same pollen upon rapid rehydration showed rupturing of 20–40% of the cells and practically no germination.