Seeds are not always sexual . . .
Apomixis, or the production of viable seeds without pollination, is the botanical version of what in animals is called parthenocarpy. These seeds are produced from flowers, just as regular seeds are, but no pollen is involved. The plants grown from such seeds are perfect clones of the original plant. Mangosteen, a tropical fruit (see thumbnail at right) produces apomictic seeds within some of the segments of the fruit. The common dandelion (Taraxacum) produces many apomictic seeds as well. What scientists would really like to know, though, is how this ability can be induced or triggered in other plants that do not produce such seeds.
A smaller species?
A plant that comes true from seed that is apomictic can give rise to what is known as a microspecies. Separated populations of these apomictic progeny may have small differences due to minor mutations; this is where the "micro" in microspecies comes in. Let's say you have twenty populations of apomictic plants from a given species, but each of the twenty populations has a small genetic variation that distinguishes it from all the others. Within each population, the plants come true from seed, so they exhibit the characteristics of a species. Since the differences between populations are so small, the individual populations are considered microspecies.
The Saharan Cypress (Cupressus dupreziana) exhibits a unique form of natural male apomixis, in which the seeds develop from the genetic content of pollen, not from ovules. This means that the entire genome is derived from the "male" side with no contribution from the female side! Saharan Cypress is very rare in native habitat, with a population of less than 200 trees situated hundreds of kilometers from any other trees. Most of these specimens are over 2000 years old. Their spread is limited due to the increasing desertification of the Sahara. Fortunately, this tree has been propagated and is being cultivated in other locations around the world, including southern and western Europe, and Australia.
Scientific study of the underlying processes that result in apomixis may enable access to new types of genetic combinations. The new plants that would result are presently impossible to develop through standard plant breeding procedures.
The Future of Agriculture?
Development of apomictic crop plants holds the key to a big change in agriculture. These would be plants that come true from seed, yet whose progeny cannot be contaminated by cross-pollination from other varieties of the same crop. The technology would enable hybrids to be reproduced more economically from seed without repeating the cross each time to obtain new crop seed. Farmers would be able to grow next year's crop with seed from this year's crop and expect that the next crop would be genetically identical to the current one. Of course, any marketing of newly developed hybrid crop plants would require that the new plants be made apomictic in order to become commercially viable. Significant obstacles to the development of this technology still exist, as do a number of potentially serious dangers to biodiversity and natural systems. Some experts feel that commercialization of apomictic plant technology may still require up to 20 years. For more information about this brewing agricultural revolution, see Apomixis: A social revolution for agriculture!.
Image credit: Public Domain image