Collection and Storage of Cycad PollenPropagation of cycads starts with producing and germinating seeds. This seems to be the most difficult part of growing cycads. Once you are working with established plants, your job is much easier. One of the keys to producing viable seeds is the proper collection, and if needed, storage of pollen. I try to make sure the pollen I use is viable. I am going to discuss how I go through the whole process. Pollen can stay viable for at least a week or two outside of the refrigerator. I don't recommend waiting this long because it is important that pollen be as fresh as possible. This will prolong its viability during storage. Using pollen that is older is still better than nothing, if that is all you have to work with. Pollen that has become inviable does no good and simply wastes time and energy--for both you and your plants.
by Tom Broome
by Tom Broome
Cycads are dioecious (possessing separate male and female plants). Male plants produce pollen and females produce seeds. Male cones are typically thinner and taller than female cones. Most species have a particular time of year when the males shed pollen and the females become receptive. This timing will vary at the same location from year to year depending on the weather. The timing of each species will also vary depending on the location in the world where the plant is being grown. This window of time can be as little as three weeks for most species, and up to three months for many Ceratozamia spp.
Male cones emerge from the apex of the plant and grow to full size. You can tell the cone is close to the time of shedding when the peduncle (stem under the fertile portion of the cone) is visible. A few days before pollen is shed, the cone will elongate and cone scales will loosen. When I see this, I tap the top of the cone slightly with my finger to see if the pollen falls out of the cone. If it is a very small cone, it is best to put a piece of paper under the cone to catch any pollen that may fall out. If ANY pollen falls from the cone, it is ready to harvest. Stangeria cones are the exception, and I will cover this below.
With few exceptions (a couple of Zamia species), pollen sacs are located on the underside of the cone scales. You will notice that some of the pollen sacs are ruptured when you see that pollen has fallen out. If you don't catch the male cone on its first day releasing pollen, it is best to see how many of the pollen sacs have ruptured. If all the pollen sacs have ruptured, it may be hard to determine when the pollen has been released, and therefore may be inviable. I never collect pollen from a cone that has completely shed unless that is the only one I have to work with. If the cone is ready to harvest, gently cut it off and put it on a piece of paper. I don't recommend newspaper because it is coarse and the pollen sticks to the paper. Notebook paper works very well. Put the cone in a cool area; anywhere in an air-conditioned house is just fine. Extremely high temperatures will reduce the viability of pollen. Pollen will continue to shed for approximately five days. I collect the pollen every two days and place it in paper packets I make by folding small pieces of notebook paper and sealing the side and ends with tape. It is important to make sure that the tape covers as little of the surface as possible so that the paper packet can breathe.
Stangeria is unusual in that it sheds pollen over a 3-week period. If you cut the cone off the plant when the pollen first starts to shed, it will stop shedding and you will harvest very little pollen. Instead, every three or four days, hold a piece of paper under the male cone and knock as much of the pollen out of the cone until the 3-week period is over. You may also wait until the pollen has been shedding for ten or more days, cut the cone, and usually the pollen will continue to shed for the remaining time.
In order to store pollen for long periods of time, it is important to remove as much of the water content in the pollen as possible. Store the pollen in a glass jar or vial, avoiding plastic bags, which can breathe and are not the best for long-term storage. To reduce the water content in the pollen, place some desiccant in the bottom of the container. I use an indicating desiccant. When dry, this material is blue; as it absorbs moisture, it turns pink. By using an indicating desiccant, you can tell when it has absorbed all the moisture it can. It is impossible to tell whether regular desiccant is still dry just by looking at it. Once indicating desiccant has absorbed all the moisture possible, it turns pink. Place it in the oven and bake it until it turns blue again. This desiccant can be used over and over again. The amount of desiccant you use depends on the amount of pollen you are trying to dry out. I have found that 1/2 - 1" in the bottom of the container works well. The paper packets are then placed on top of the desiccant. By using paper packets, which can breathe, the desiccant can do its job. Instead of using one big packet for all of your pollen, place the pollen in small packets so one packet can be removed quickly without disturbing the unused pollen. I try to put enough pollen in each packet to pollinate a single cone once. If you plan to pollinate the same cone a few times, fresh pollen can be removed each time for maximum viability. Write the species name and date stored on both sides of the packet so you can tell later on how old the pollen is.
This figure shows a cross-section of the microsporophylls of a Zamia cone. The top picture shows pollen sacks that have not yet ruptured; the bottom picture shows what ruptured pollen sacks look like.
Two male Zamia cones. The cone on the left has elongated and is ready to collect; the cone on the right has not yet elongated.
This photo shows the vial, the indicating desiccant, the paper packet, and how it should be labeled.
Once I cap the vial, I place it in the refrigerator for two days. I do not place it directly in the freezer because the pollen's moisture content is too high; water expansion can rupture the pollen and render it inviable. Once the pollen has been in the vial for at least two days, and as long as the paper packet has had enough breathable area, moisture content will be reduced enough for you to put the vial in the freezer. Once the vial is in the freezer, the pollen should be good for years. I have found that pollen will stay very fresh for at least three years. I know one person who used pollen that had been stored for six years and got a good seed set. I have been told that if pollen were to be stored in liquid nitrogen, it would stay viable forever. Of course this method is not practical for most people. If you collect pollen on separate occasions, but eventually want to keep the pollen in the same container, it is best to store the newer pollen in a different vial and go through the same process in the refrigerator. Once the new pollen is desiccated, the newer packets can be quickly placed in the original container. When removing packets for use, it is important to minimize the time that the vial is open because the pollen and packets can reabsorb moisture. This is another reason to use several packets instead of removing a small amount of pollen each time from one larger packet. Once you remove a packet, use the pollen as soon as possible.
Pollen loses viability quickly at room temperature and even faster at higher temperatures. Pollen can stay viable at room temperature for several days, but I attempt to maximize its viability so that more good seed is produced in the long run. Just because an entire cone is pollinated does not mean all of the seeds will germinate. Quality of the pollen has a great deal to do with how many seeds in each cone are viable. Another reason to keep moisture content low in pollen is to lessen the chance for fungus to grow on and kill the pollen. When I send pollen to someone who lives far away, I send it in a vial containing desiccant. This will keep the viability high. If the shipping time will be longer than one week, I add a cold pack to the box, which seems to help. I have been thinking about making a shipping container that would have two compartments. The inner, middle compartment could hold the vial, and the outside compartment could hold ice to keep the vial cooler while shipping. If dry ice were used in the outer compartment, pollen most likely could be shipped anywhere in the world without loss of viability. (Keep in mind, though, that all cycads are CITES listed, so sending pollen out of the country will require a CITES permit.)
I would also like to remind everyone that all parts and products of cycads are poisonous. This includes pollen. I have known people who have been hand-pollinating their cycads for decades and have never shown any obvious side effects from this, but I would still recommend using a mask and gloves when handling pollen.
I hope this information helps everyone store pollen correctly to insure its viability. This is especially important for those who are mailing pollen to others. More and more people are propagating their cycads every day, and they are also coordinating their efforts with others by sending pollen to people who do not have male plants. I hope this article will help everyone produce more seeds and, eventually, more cycads.