Classical plant breeding
The purpose of classical plant breeding is the creation of new lines and varieties with improved agricultural traits such as higher yields, increased tolerance or resistance to diseases and adverse environmental conditions.
Upon selection of ornamental plants, the goals are targeting development of varieties and lines with altered or improved appearance. In order to launch a successful breeding program, a number of conditions should be met, however, one of the major ones is the existence of a collection of representatives of the particular plant species or multiple species that possess different characteristics. Such a collection allows the breeder to select appropriate members whose various qualities would like to combine into a new variety through a series of targeted cross-pollinations. In a given collection there may be a member with high economic indices of yield, but the respective member could be susceptible to environmental changes or diseases leading to significant losses in years with unfavorable conditions or which makes it inapplicable for different geographic areas. On the other hand, another member in the collection may not have the desired high yield, but in turn could be resistant to environmental changes or diseases. In this case, the breeder would like to combine the high yield of one of the members and the resistance to adverse conditions of the other member into a new variety. Unfortunately, only one cross does not lead to the creation of a new variety. It takes a number of successive crosses and selection of lines possessing the demanded by the breeder qualities – a process that along with the registration of the variety may take, in some cases decades.
Classical breeding utilizes largely the natural diversity of the various species of plants as a source of valuable economic traits and the creation of new varieties based on their targeted combination as a result of intra- and inter-specific crosses. The existence of this natural diversity is due to the gradual changes in the organisms’ genes (mutations) that occur spontaneously and when these changes are not lethal, they are transmitted in the offspring.
Some mutations can create advantage for the particular organism which is extrinsic for the rest of the representatives thus imparting it a new quality. In other cases, mutations may have adverse and even lethal effects. The process of occurrence of such changes is slow and in some cases, in order to increase the naturally existing diversity, the breeders use methods of mutagenesis, wherein as a result of external interference (eg. treatment of seeds with radiation or chemical agents) random changes in the genome of the treated species are created, some of which may have beneficial character and be used for breeding. For example, this is the way cv. “Elejna” and cv “Janina” were created by Prof. Dr. Raycho Tsvetkov – varieties of the Bulgarian oil-bearing rose (R. damascena Mill) from which only a single genotype exists in the country and whose representatives have been obtained by clonal propagation from a common ancestor. The disadvantage of this method is its random character and the lack of information on the number, type and location of changes occurring in the genome of the treated species.
The modified species by radiation or chemical mutagenesis are not treated as genetically modified organisms (GMOs) and are not a subject of regulation by the Law on GMOs in Bulgaria.