Seems I’ve heard that pollen can be frozen for future use. Does anyone know how long it can be frozen and still be viable? I’ve found a florist rose that I would love to use as a pollen parent next spring. Any thoughts?
If the pollen is thoroughly dry when placed in the freezer, and in air tight containers, it will easily last 9 months, probably 12.
Paul
Thanks, Paul, I’ll give it a try.
Dear Jean,
Paul is right. I did a study looking at the degradation of pollen over time at a few different storage temps and reported it at the Rose Research Symposium this past Sept. Pollen stored at 4C (fridge) went downhill fast. Pollen stored in a typical freezer (-20C) was still viable after a year as well as at -80C. I germinated the pollen grains in sugar water and measured pollen tube length (estimate of vigor of the live grains) and found that -80C preserved pollen tube length better and then resulted in more seeds per hip than -20, but most of us just have a -20C freezer and it will work.
Sincerely,
David
P.S. I typically use film canisters and airdry the anthers and then snap the cap on and put the canisters in the freezer. I then let them warm to room temp before opening them so condensation doesn’t get the pollen wet inside before I use it.
Pollen kept in a refrigerator freezer for 12 months will maintain its viability. This treatment did not seem to affect hip set or seed number. Germination will be observed this coming spring.
I did an experiment this year using a slightly different method.
I also collect my pollen and dry it, but I dry it really hard, over a drying agent (the brand name is “Driright” or some such thing). I believe it is silica-based.
I collect the pollen, air-dry at room temperature for 1 or 2 days, and then place it into small glass vials (about 3 or 4 ml), and place the vials sideways, without their caps, onto a bed of drying agent in a tightly sealed Tupperware-type container in the refrigerator. After a week or more, I put the lids on the vials tightly. I then continue to store the pollen in the refrigerator, but without the drying agent. The vials are allowed to warm to room temperature just before use, to prevent condensation. If I use a vial a lot, I may put it back on the drying agent without the cap for a few days.
For my experiment, I used my pollen that I collected in early summer 2004 to make pollinations last spring (2005). The pollen was then about 10 months old. I am a long way away from pulling the data together, but the old pollen did work more often than not. I only used pollen that had worked well the previous year, and all of the female parents I used also have good fertility. I get the impression that there was a drop in the number of seeds per hip.
I am sure that freezing would be better, but I had a shortage of freezer space until this winter. I may try freezing next year for comparison. I imagine that self-defrosting (frost-free) freezers would be a bad idea, as they warm up briefly during each defrost cycle.
Dri-rite Dessicant is anhydrous calcium sulfate. That will have a different ability to dry things than silica gel. I wouldn’t have a clue which is better for keeping frozen pollen happy. For seeds in general you don’t want them too dry, just a certain % water content, for longest life. Very likely it’s the same principle for pollen but David Z. may have done more on this subject than anyone. So if you just want 1 yr carryover follow his advice.
Hi Larry, That’s a great question about moisture content. I haven’t done comparisons with roses. I suspect that Roger’s refrigerator success may be due in part to lower humidity using the dessicant. I did not use dessicants in my experiments and noticed that the yellow color of the pollen faded more quickly with the refrigerator treatment than frozen treatments. Warmer air can hold more water than colder air. I have frozen and used lots of lily pollen the past few years. There is a report like you mention Larry that getting it too dry is a problem. When it was dried with dessicant one needed to slowly rehydrate it before use or it would be damaged. They found that just airdrying it, freezing it without dessicant, and letting the canisters warm before opening them worked best and was easiest. I thought of manipulating humidity for the rose work, but I didn’t think I had the right resources to alter and monitor it. Henry K. probably would know how being a chemist. If I understand right there are different dessicants that at different temps tend to result in certain % humidities in the air around them.
Sincerely,
David
It was more than 30 years ago when I kept pollen frozen for about 9 month. The next summer I used the same seedparents with frozen and fresh pollen for control.
Just like Rodger Mitchell wrote, there was a drop in the number of seeds per hip with the frozen pollen. I only tried it once and its too long ago to give the exact numbers, but the frozen pollen gave about 6 seeds per hip in comparison to about 10 for the fresh pollen.