Dispatch 9: Send in the Clones

Today the greenhouse has its first plants: eight of them. They are clones, donated by the propagation station at La Reunion. Of two genetic varieties, known as 1188 and 919.

Cloning is an efficient way to reproduce high-yield, disease-resistant seedlings, which can then be planted in place of aging and inferior trees. In the lab back home, Guiltinan and his team have developed two cloning methods, a high-tech and a low-tech approach. The first, somatic embryogenesis, involves taking the immature cocoa flower from a proven plant and removing the sterile stamens. These staminodes, five to a plant, are placed in culture and induced with plant hormones to produce embryos, which eventually grow into plants. Since there is no pollination involved, the embryos (and plants) are identical to the original plant. "With this technology," Guiltinan says, "we can take elite genotypes and propagate large numbers of plants in a short amount of time. The question is, are these plants normal?"

To find out, he and his lab are currently field-testing several hundred plants on the island of St. Lucia, monitoring root structure, growth rate, yield, and fertility. The other, low-tech approach that Guiltinan and his team have developed is called bent-wood gardening. In this technique a chosen plant is topped and then bent parallel to the ground. The horizontal main stem then produces shoots which grow vertically. These orthotropic shoots, when cut and rooted, produce clones with true tree structure, as opposed to plagiotropic cuttings, which produce a bush. From ten good plants, Bent-wood gardening can produce perhaps a hundred more in a few years, a marked improvement over most rooted cutting techniques. The method is much less expensive than embryogenesis, and easy for farmers to learn and practice. The great advantage of embryogenesis, on the other hand, is that a single flower can produce over 8,000 plants in one year.

Whatever the propagation technique, preserving genetic variability is an important consideration. For one thing, almost all cocoa plants are self-incompatible; that is, plants of the same variety cannot pollinate each other. For cross-pollination, and as a hedge against disease, it's important for a farmer to grow several types. "The idea is to have good plants, but as many varieties of good plants as possible," Guiltinan says.