A Seminar for SWR/ABS, May 1999 - Freda Holley
ref:http://absastro.tripod.com/culture/pollination.htm
"Why save seed?", you ask when begonias are so easy to propagate from leaf and stem? Because each new plant of a species we can grow adds to the likelihood that that species will survive and adapt to the captive conditions in which we grow it. When we grow many different seedlings of a species, we capture more of its genetic diversity and secure it to the future. My primary purpose with every species I grow is to set seed and grow them out. Until I have done this, I never really feel that I "know" a species. Over and above that purpose, however, is another fascinating reward. The young seedlings are often gorgeous with leaves that do not even resemble their adult form. The process of securing the future of species through seed comes in two steps: setting them and saving them.
Setting Seed - The Mechanics
The actual mechanics of setting seed in begonias is very easy. Most begonias have both male and female blooms on the same plant. The female is easy to recognize because in back of the flower petals - or tepals as they are called in begonias - is the ovary. In front of the tepals are the styles where the receptacles for the pollen are located. The male flower has tepals and stamens on which is located the pollen. To make seed, one must simply transfer the pollen onto the styles. I usually do this by folding back the tepals on the male flower and brushing the stamens over the styles - very gently so as not to damage them. Some use a small paint brush to transfer the pollen. This act of pollination should occur when humidity is lowest, usually around noon. In many species this transfer is so easy that the plants accomplish it on their own. B. fischeri, B. franconis, B. humilis - the male flowers being positioned above the female and simply shedding their pollen down onto the females. However, in most begonias it is not so easy and we must help the process along. Indeed some are so difficult that no seed have been set in culture; in some cases, the plants have even refused to bloom. In fact, getting a species to bloom is often the first challenge.
Getting Bloom
Each species has its own flowering agenda requiring the right age, time of year, temperature, light and overall environment. Some begonias begin to bloom their first year from seed, including most of the semperflorens and and even such exotic species as B. dipetala or B. U062. However, I find that most canes must reach two or more years in age before they bloom - on a few I have waited up to five years.
The season for bloom in begonias is varied. In general, canes, semps, tuberous, and shrubs bloom in the summer; thick stems and trailing scandent in fall and winter; and rhizomes in winter to spring. In fact, many species with other conditions being right will even be everblooming. Temperatures are very important. In the Ozarks, my canes bloomed heavily right through the summmer, but in Nacogdoches, many canes stopped blooming with temperatures approaching 100 degrees for many days. B. gehrtii, a rhizomatous begonia that likes it downright cold bloomed better for me when night temperatures approached freezing; it bloomed later and less readily in the greenhouse where temperatures were kept at around 50 degrees at night. Thus, one really has to get to know a particular begonia to predict its blooming behavior.
Light has its own effect. In general, most begonias will bloom better in high light, but again this can vary. My B. rajah bloomed happily in a north window in Ozone. In Nacogdoches it refused to bloom on my sun porch and then in the air conditioning under bright florescent light. Once more placed in a north window, although with much lower light than it had gotten in Ozone, it grew happier and is now blooming away. B. maculata kept in heavy shade bloomed in late summer, but placed where it got full sun for about 7 hours a day, it began blooming in early spring and was still blooming at Christmas in the greenhouse. So, if you aren't getting bloom, try different settings. It is nice to have several different plants of a species so this can be done simultaneously. Some environmental effects are more subtle. For example, many rhizomatous species must have a set number of hours of darkness to trigger bloom—ten hours of dark is the usual amount quoted although I believe the degree of reduction may be the key rather than an exact number. I have had rhizomes that came home with me from bright greenhouses and were placed in heavy shade in my yard sometimes begin to flower even in summer. However, if you want your rhizomes to bloom, take care that you don't have night or security lights that interfere.
Finally, remember that phosphate is the miracle food ingredient for bloom. Giving plants a high dose of this before and during bloom really does work.
Getting Seed
Just because a plant blooms is no certainty that it will set seed. Nature seems to program plants so that they will not waste energy making seed if the conditions are not right. In Ozone, my summer bloomers set seed all summer because temperatures seldom went above 90. In Nacogdoches I got seed in spring and hopefully will again in fall, but most of the canes won't set seed in temperatures above 90. Watch your impatiens plants (single); if they are blooming and not setting seed, the culprit is probably the temperature.
Humidity is also important; pollen often won't release if the humidity is too high. In this case, you may be able to take the male flower into a dry area such as in the air conditioning and get the pollen to release. If male flowers tend to fall before the female open, you may save pollen too. Dry it and keep cool until your female is ready. Some even exchange pollen by mail. Light must be right here too. Sometimes, though this effect too can be difficult to predict. I had a B. U347 on which the male blooms refused to open even when placed to get good light in the greenhouse; then one day I noticed that on its back side where the plant was heavily shaded, the male blooms were opening!
Age plays a role here too. I've found that many plants will not set seed on their first blooms or even in their first bloom cycle. B. bufoderma was one that bloomed heavily for several years before I finally got it to set seed for me. Then, those first seed were not viable, that is they refused to germinate. Finally, one year the seed became viable. Keep trying?
When you seek to hybridize, another important determinant in getting viable seed is genetics. The genetic matter of two different species (within a species of course, genetic matter is the very close) must be compatible to produce viable seed. This is fundamental, of course—a petunia and a begonia will never cross, but even within the begonia family incompatibilities occur. Chromosome number is one genetic factor that influences reproductivity although not the only one. Begonia plants vary in the number of chromosomes they carry ranging from a low of 22 up to as high as 156. These come in pairs. At reproduction, each male pollen grain and each female ovule have one-half the number of chromosomes as in the plant cells. At fertilization, the one-halts come together to create the seed with a full complement. An easy way to visualize this happening is to pretend there were a begonia with 10 chromosomes—put the tips of your ingers together to see that they fit to make a "steeple flower" —now take the tips apart—you have 5 chromosomes on one hand (the male) and 5 on the other (the female). You can join them to make the 10 chromosome plant again. Or if you want to "hybridize" you can match your 5 fingers to another person's 5 fingers to make a "new" steeple flower. But say, you had a friend who had 7 fingers, when you tried to join your 5 with his 7, there would be no match and it wouldn't work.
This, of course, is a very simplified illustration and as we all know begonias are anything but simple. The genetic matter must also be compatible; some allege that begonias from different regions of the world do not cross well. Also, chromosomes sometimes do strange things—doubling, tripling, breaking, losing and gaining genes. So we can never say two begonias with different chromosomes or genes won't cross. In general, however, it doesn't happen and if it does, the plant is not likely to be a healthy, strong one.
Let me also put in a word in favor of hybridizing for its usefullness in preserving genetic variability. At times, species are so difficult for us to grow that they may disappear from cultivation. For example, B. olbia used to be quite common, now it is rarely seen, but we have some of its genetic variability carried on in B. 'Argenteo-guttata' and other hybrids.
Saving the Seed
Harvesting
So now, you've pollinated and the seed appear to have set. I've read that when seed set, the female tepals will close and fall. I find this to be true sometimes and sometimes not. In some varieties the tepals will persist and hold to dryness. Usually, however, you can see the pod visibly swell as the seed grow. Pods without seed will be very thin and papery. Leave the pod on the plant until it is dry and brown. If it should fall before this stage and has been on the plant for some time, you may try to save it if the seed is precious by placing it where it can safely dry off the plant. Sometimes this seed will germinate, sometimes not. After the seed pod has dried on the plant, I gather the seed in glass baby food or mushroom jars. I use a permanent marker to label immediately (Don't even think you will remember later what the seed was from!). Then I place the open jar in a place where further drying can occur—on top of a florescent light fixture, in an oven with the light or pilot on, anywhere that contributes to drying. In the humid outside environment, you will think the seed pod dry, but there will be much moisture left and this must be extracted. Dryness, I believe, is even more important than a cool temperature to save seed.
Storing the Seed
Since all the seed pods do not necessarily mature at the same time, you can continue dropping them into the labeled jar until you have them all or the jar is as full as will safely continue drying. When I have a number of these jars to process, I spread newspaper at the dining table. I have a plastic ice cream container to receive the waste, small and large sheets of paper, seed envelops, a metal tea strainer, a notebook, and a pen and a permanent marker. At the same time I have a container of one inch plastic portion cups filled with wet seed planting mix. I break the seed pods over a small sheet of paper (note size) placed over a larger sheet trying to get as little of the papery pod as possible into the seed that fall. Unless the seed is clean, I pour the seed through the strainer onto a second small sheet; continuing back and forth until the seed is as clean as I can get it. I've read that you can just roll the seed on the paper to free them from the debris, but my debris always slides better than the seed roll! It is important that your strainer be metal, not plastic as the seed will cling to the plastic. Next, I crimp the center of the small sheet and pour the seed into a glassine seed envelope. Before I discovered that these envelopes can be bought from the Commercial Division of Park Seed Company, I used little squares of foil, folded tightly, then wrapped these in paper for labeling. But, the tiny seed would always manage to filter out. The seed envelopes are well worth their price of about $30/thousand. Finally, I use an SOS pad to remove the marking from the baby food jars and place them in the dishwasher before reusing them (the tiny seed persist where you least want them). I also place a tiny portion of the seed into the germinating mix for testing. Then I use the marker to label both the portion cup and the glassine envelope. After trying various labeling schemes, what I use now is a label such as "99.97 B. egregia". This tell me that I gathered this 97th batch of seed in 1999. I use the pen to record the same info in my notebook, adding any relevant information such as "bloom fell early" or "first seed from this plant". This labeling will be very important if you have to go back several years to find seed you want. When I have finished with all the seed for the day, I place the seed envelopes together in a Ziplock snack bag which goes into a larger 1999 Ziplock bag. These go into the refrigerator crisper - or if you are like a few of us seed nuts into a small seed refrigerator. The cups are placed into a foil baking pan with clear plastic cover under florescent lights. When germination occurs, the time is recorded in the notebook. Thus secured, you may save the seed for long periods of time. Germination has been reported on begonia seed saved for 20 or more years and I have personally germinated seed 14 years old. However, I believe that the fresher the seed the better the germination and the stronger the plants you will get. For securing species, it is probably wise to have a plan for growing out new stock on a regular basis.
The whole process is really quite easy and mechanical once you have established the routine and the ideal timing for saving seed in your setting. There are almost always jars of seed setting around waiting to be processed at my house. Not all of us will be able to get seed of every species in our environment, but some will no doubt prefer your environment and set seed for you when they will for no one else. Let's save our species!
這凹凹凸凸的美麗海棠，B. crispula，原生地在巴西熱帶低中海拔的雨林底層。
