|
|
 Fall/Winter
1997 |
||
Not Just Another Pretty Flower
The genus Exacum is not entirely new to ornamental horticulture. About 65 known species range from western Africa through Madagascar to the Himalayans, and one in particular has made its way into commercial greenhouses. Exacum affine comes from the island of Socotra off the southern Arabian peninsula, and has been on the market as a potted plant since the mid-1970s. Known commercially as Persian violet, it has small blue, bluish purple, or white flowers. "Dr. Craig's research on Exacum affine is what led to my current project," Riseman says. "Just as I was finishing my bachelor's degree and was ready for graduate school, he informed me there were large-flowered types of Exacum from Sri Lanka that were worth looking into. A former graduate student of Dr. Craig's had collected Sri Lankan Exacum germ plasm, and my project was to evaluate the reproductive biology of the plants. I was really taken with the new Exacum plants the first time I saw them. Whereas the flowers of Exacum affine are about 1/2 inch in diameter, some breeding lines of Sri Lankan Exacum have flowers up to 2 inches wide. The plant also is exceptionally durable. It stands up to extensive rain, heat, and drought. We think it has the potential to be an excellent annual bedding plant as well as a potted flowering plant. Some long-stemmed types also could make terrific fresh-cut flowers." Riseman is breeding variations of the species for marketing. "I've learned that there's a lot of creativity in plant breeding," he says. "A person can be taught genetics, but to apply that to a living system for an esthetic purpose, you have to have a good imagination. You need to be able to look at the qualities of one flower and envision what would happen if you combined those with qualities of another. I've been experimenting with these combinations for years, and there's a big difference between the original Sri Lankan Exacum species and what we have now." Successful plant breeding also means eliminating characteristics that would make a plant less than ideal for growers. "Most of the time, you can't take a wild species that has grown at the foot of a mountain for a millennium, plant it in a pot, and expect it to perform well," Riseman explains. "You either have to satisfy the plant's native cultural requirements or, in the case of plant breeding, breed it toward domestic cultural conditions so it's easier to grow in captivity. In effect, what you're doing is domestication, just the way people have domesticated certain animals so that they can live among us."
It often takes many years to breed a plant for commercial purposes, and in the case of Sri Lankan Exacum, Riseman thinks the work has been a success. "I believe we have some patentable crosses right now," he says. "But before we go public with them, we need to make sure we can market them effectively. Using the botanical name Exacum may not be a good idea, because it doesn't exactly conjure up the image of a beautiful flower. We're still trying to decide on a more appealing name for these plants, one that will reflect their beauty as well as their origin." Creating the next garden beauty isn't the only goal of Riseman's research. He also is studying a peculiarity of the species that could have far-reaching implications for plant science. "There's a nutritional problem with some of the genetic crosses we've produced," Riseman explains. "While certain plants grow just fine, others display classic symptoms of zinc deficiency. They have small, tightly crinkled, pale yellow leaves and buds on top. Zinc is an extremely important micronutrient–it plays an essential role in the transformation of enzymes that lead to the development of DNA, the building block of all life. But a lot of what zinc does in living systems is still a mystery. If I can learn more about what's happening in these zinc-deficient plants, I might be able to help unravel that mystery. "The zinc-deficient specimens look pretty bad, and if I were a commercial breeder, I would want to select them away from this characteristic as quickly as possible," Riseman explains. "But as a researcher, I find these plants very valuable. I'm comparing their performance to that of healthy specimens in many different soils and under various environmental conditions. I'm trying to relate my findings to what we know about the original species collected several years ago. I hope to travel to Sri Lanka and collect samples of soils and plants of the original species and study how environmental factors such as light, temperature, and rainfall affect their nutrition. Perhaps what started out as a survival mechanism is being expressed now as a zinc deficiency in these crosses we've produced. "The research could have very practical applications," Riseman continues. "For instance, in many areas of the world, arable soils are zinc deficient, and this limits crop development. Understanding how plants absorb zinc from soil could help agronomists make this farmland more productive. Also, once plant scientists understand how plants use this micronutrient, they may be able to transfer that mechanism through biotechnology. They could isolate the gene or genes responsible for zinc uptake and put those genes into a plant that can tolerate high accumulations of zinc. Plants that can absorb high amounts of substances are called hyperaccumulators. Hyperaccumulators of zinc could be used for bioremediation. For instance, they could be planted at mine sites where accumulations of the metal have reached toxic levels. Once these plants remove the zinc from the soil, they and the zinc can be disposed of safely." Riseman is considering
becoming a professional plant breeder after he completes his Ph.D. "I'm
also interested in doing some international work, possibly with an
organization such as an international crop development center or the
Peace Corps," he says. "One thing's for sure, I'll continue
to work with the physiology and genetics of plants. No matter how much
you learn about them, there's always room for more discovery." |
||
|
Penn State | College of Agricultural Sciences | ICT Copyright - Alternative
Media - Affirmative
Action |
The
blue of an October sky, the violet of a stormy sunrise, the purple
of ripe plums. These, and many variations, are the colors of a remarkable
flower called Sri Lankan Exacum. Its native habitat is the tiny
island country once known as Ceylon, now Sri Lanka, but someday soon
the flower may flourish in gardens right here in the United States. "It's
very beautiful and one of the few plants that can produce blossoms
that are truly blue–a color hard to find in flowers and much sought
after by horticulturists and gardeners," says doctoral candidate
Andrew Riseman, who began studying with his adviser, plant geneticist
Richard Craig, during his freshman year. "I wasn't satisfied with
my major and even considered leaving the university, but Dr. Craig
encouraged me to stay and learn about plant breeding. I've never regretted
my decision–it has led to my research on this very interesting
plant."
