Marker-assisted screening of promising forms in the strawberry breeding

The results of the use diagnostic DNA-markers in the breeding of strawberry (Fragaria × ananassa Duch.) were shown. The carriers of target alleles of red stele root rot resistance (F. virginiana Duch. ssp. platypetala, Bylinnaya, 69-29 (Feyerverk × Bylinnaya), 72-24 and 72-71 (Privlekatelnaya × Bylinnaya)), anthracnose resistance (Borovitskaya, Sudarushka, Elianny, Troubadour, 933-4 (F. virginiana Duch. ssp. platypetala × Rubinovyy kulon)), high mesifurane content in fruits (F. orientalis Los., F. moschata Duch., F. virginiana Duch. ssp platypetala, Lastochka, Torpeda, Flora, Samson, 932-29 (F. virginiana Duch. ssp. platypetala × Feyerverk), 56-5 (Gigantella × Privlekatelnaya)) and γdecalactone content in fruits (F. orientalis Los., F. moschata Duch., F. ovalis Rydb., Bylinnaya, Kupchikha, Sonata, Vima Tarda) were identified. These genotypes are valuable initial forms for involvement in the breeding process to improve the strawberry assortment.


Introduction
Strawberry is the most widely cultivated berry crops. Strawberry plantations are located in 78 countries of the world and the harvest of strawberry fruits exceeds 2/3 of the berry world production [1][2][3]. However, in current conditions of climate destabilization, massive development of diseases of various etiologies and increased attention to the quality of the berry products, many strawberry varieties do not sufficiently meet the market requirements. In this connection, it is necessary to carry out targeted breeding work in order to create strawberry genotypes characterized by a complex of such traits as resistance to unfavorable factors of growing conditions, high stable productivity and commodity consumer qualities of fruits [4,5].
A necessary condition for the implementation of the problem is the identification of sources and donors of loci (genes and QTLs) of valuable traits, and attraction and creation of polymorphic source forms. An important stage in the strawberry breeding is the identification of initial parental forms for hybridization. They should not only be characterized by a complex of significant breeding traits, but also, to a certain extent, transmit them to their offspring, which makes it possible to increase the efficiency of creating valuable genotypes.
One of the topical directions for intensifying the process of creating new forms is the combination of classical breeding methods of with breeding technologies based on DNA markers (marker assisted selection). The advantage of DNA marking technology is to assess the presence of significant traits not by their phenotypic expression, which is formed under the influence of environmental conditions, but directly by the presence in the genome of target alleles. In addition, the use of molecular DNA markers allows detecting DNA polymorphism, establishing genetic relationships and the origin of varieties and forms, as well as identifying new genes and QTLs. [6][7][8][9].
Strawberry (F. × ananassa Duch.) is a difficult object for molecular genetic analysis, which is due to the combination of several basic genomes in one genotype, a high level of ploidy (8x) and polygenic determination of many valuable traits. However, the active development of technologies of molecular genetic analysis of the genome has made it possible to deepen knowledge of the mechanisms of determination and inheritance of a number of strawberry significant traits and to map some candidate genes and QTLs [10][11][12].
Currently, DNA markers are most actively used to identify genetic diversity, mapping, and genetic passportization of strawberry varieties and forms [13][14][15]. The use of molecular markers in strawberry breeding for the identification of significant trait genes will increase the efficiency of the strawberry breeding, reduce the time to identify donor qualities of genotypes and select the initial parental forms for hybridization.

Materials and Methods
The studies were carried out in 2020-2021. Biological material was represented by wild species of genus Fragaria L., strawberry varieties of Russian and foreign breeding, and promising hybrid seedlings, obtained at the FSSI "I.V. Michurin Federal Scientific Center".
Reaction mix in final volume 15 μl containing 1.5 μl Taq-buffer, 0.2 mM of each deoxyribonucleotide triphosphate, 2.5 mM magnesium chloride, 0.2 U Taq DNA polymerase, 0.2 μM of each primer and 20 ng of genomic DNA.
Amplification products were separated by electrophoretic method in agarose gel (agarose concentration -2%, running buffer -1x TBE). Amplicon sizes estimated were performed using the Gene Ruler 100 bp DNA Ladder (Thermo Fisher Scientific, USA).