Researchers Can Cross Non-Interbreeding Plants

Researchers of the All-Russian Scientific Research Institute of Plant Cultivation, Russian Academy of Agricultural Sciences (St. Petersburg) jointly with their colleagues from Germany and Finland have grown up new lines of Solanum cultivated plants via the somatic hybridization method – hybrids of wild species of plants of the Solanum family with cultivars of tomato and potato, that posess new useful properties.

Potato and tomato – the plants that occupy the honorary place in the menu of mankind – belong to the Solanum family. So do multiple wild species inhabiting Mexico, they are inedible, but possess the qualities interesting to selectionists, such as disease and vermin stability, salt-tolerance, psychrotolerance. However, this interest has remained theoretical up to recently: the majority of wild species was reluctant to interbreed with cultivars. Therefore, the researchers of the All-Russian Scientific Research Institute of Plant Cultivation, Russian Academy of Agricultural Sciences (St. Petersburg) jointly with their colleagues from Germany and Finland set about cultivating new Solanum species via the somatic hybridization method.

There exist different methods for introduction of required genes into the cultivated plant’s genome. Genetic engineering which is now much talked about is only one of them and far from being the most important if we recall the centuries-old history of selection. Interbreeding of species and lines, pollination of one plant by the pollen of the other are still used by selectionists. However, such interbreeding, particularly the interspecific interbreeding does not always work well. In the 70s-80s, a new method emerged that allowed to overcome the barrier of non-interbreeding: somatic hybridization.

Non-gametal cells are called somatic, they are not related either to pollen, or to the germ of the seed, they are taken, for instance, from the leaf. Cultivation of a full value organism from a somatic cell is called cloning. Animal cloning is one of the most outstanding achievements in biology of recent years, as for plants, cloning is the most commonplace familiar to anyone who implanted a violet leaf or a pussy-willow cutting. In the laboratory conditions, researchers can grow a full value plant from a small bit of tissue (to this end, specially cultivated mass of dedifferentiated cells called callus is used), and from a single cell.

However, another way can be chosen: to make two cells belonging to different plant species merge. (These cells deprived of hard membranes are called protoplasts.) That gives rise to hybrid cells, which combine gene material and properties of two plant species, including those species that cannot be interbred in standard ways.

One more important thing should be kept in mind. Mitochondria and chloroplasts are microbodies that possess their own genome and propagate in the cytoplasm. Mitochondria account for the cell energy supply, chloroplasts are responsible for photosynthesis. Obviously, a lot of important agricultural properties of plants are particularly connected with them. In case of common propagation, a plant gets mitochondria and chloroplasts only through the maternal line: as a rule, mitochondria and chloroplasts are absent from the male gametal cell. In case of somatic hybridization, both parties make equal contribution, a selectionist being able to make additional benefit from this fact.

The Russian-German-Finnish experiment involved cultural varieties of Solanum tuberosum potato, on the one part, and wild Mexican varieties of the same Solanum genus, on the other part. After the cells merged and plants were regenerated from the hybrid tissue, the researchers carried out recurring reciprocal interbreeding with the cultural variety until a potato line with stable genome was obtained. Similar experiments were carried out with tomato and its wild congeners. Certainly, the researchers checked thoroughly what the hybrid genomes represent. It was demonstrated in practice that some hybrid lines do possess new useful properties, for example, increased stability to virus diseases.

Journalist often ask researchers of the All-Russian Scientific Research Institute of Plant Cultivation when they are going to make kitchen gardeners’ favorite dream come true and will cultivate the tomato-potato, which will have tomatoes on the branches and tubers under the ground. In Germany, such a hybrid was created back in the 80s, but unfortunately, neither fruit or roots of the regenerated plant were edible. Further experiments will show if the problem can be successfully solved.