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Setting and Saving Seed for Species ConservationA Seminar for SWR/ABS, May 1999 - Freda Holley
"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 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.
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
Storing the Seed
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!