Citrus collections from extreme growing regions can be an important source of tolerant germplasms for the breeding of cold-tolerant varieties. However, the efficient utilization of these germplasms requires their genetic background information. Thus, efficient marker systems are necessary for the characterization and identification of valuable accessions. In this study, the efficiency of 36 SCoT markers and 60 InDel markers were evaluated as part of the broad citrus collection of the Western Caucasus. The interspecific and intraspecific genetic diversity and genetic structures were analyzed for 172 accessions, including 31 species and sets of the locally derived cultivars. Single markers, such as SCoT18 (0.84), SCoT20 (0.93), SCoT23 (0.87), SCoT31 (0.88), SCoT36 (0.87) и LG 1-4 (0.94), LG 4-3 (0.86), LG 7-11 (0.98), and LG 8-10 (0.83), showed a high discriminating power, indicating the good applicability of these markers to assess intraspecific diversity of the genus Citrus. Overall, SCoT markers showed a higher level of polymorphism than InDel markers. According to analysis of population structure, SCoT and InDel markers showed K = 9 and K = 5 genetic clusters, respectively. The lowest levels of genetic admixtures and diversity were observed among the locally derived satsumas and lemons. The highest level of genetic admixtures was observed in the lime group. Phylogenetic relationships indicated a high level of interspecific genetic diversity but a low level of intraspecific diversity in locally derived satsumas and lemons. The results provide new insight into the origin of citrus germplasms and their distribution in colder regions. Furthermore, they are important for implementing conservation measures, controlling genetic erosion, developing breeding strategies, and improving breeding efficiency.

The article analyzes the collection of citrus crops of the Federal Research Center "Subtropical Scientific Center of the Russian Academy of Sciences" (FITC SNC RAS) in Sochi. The bioresource collection is kept alive in the field and in a container culture for varieties; the collection is represented by the genetic and ecological-geographical diversity of C. reticulate Blan varieties. var unshiu.Tan., C. limon Burm., C. sinensis Osb., C. paradisi Macf., C. maxima Burm., C. medica L. and other species and relatives introduced from Japan, America, China, Italy, Spain, Nicaragua, Abkhazia. The collection is constantly updated with both introducers and new varieties and promising hybrids bred in the Center. Lemon and tangerine groups are widely represented. 19 sources of economically valuable traits that are included in the breeding process have been identified and described from the collection. Citrus reticulata Blanco is of great importance for the humid subtropics of Russia as the most winter-hardy species. Breeding work is being carried out, which is aimed at breeding early-maturing, short-term, stunted forms of mandarin. Ten varieties of mandarin have been created: Sochi 23, Pioneer 80, Krasnodar, Sugar, Black Sea, Millennium 1, Millennium 2, it is most adapted to extreme growing conditions. Because of hybridization, 21 promising forms of mandarin were identified, which are of interest for further breeding work. Large-fruited hybrids 98-1; 99-2; 99-4 were noted, the average yield of which was 3.4 kg /day, these forms are late-ripening (II decade of November). Forms 2-2; 01-4; 01-04; 97-3; 2-5; 2-5 they are characterized by early maturity (II decade of October), stunting and stable yields of 2.6 and 3.0 kg/day. Samples for ornamental gardening are presented: C. ? bergamia, C. ? bergamia var. Melarosa, S. Lemon "Del Brasil", C. ? limetta, C. ? limonelloides, C. verrucosa Tan., C. hystrix DC., as well as two forms:202 (Fortunella margarita?C. reticulata); 78 (Fortunella Margarita?C. reticulata).

The article presents a genetic collection of citrus crops formed in the humid subtropics of Russia on the basis of the Federal Research Center "Subtropical Scientific Center of the Russian Academy of Sciences", Sochi. The gene pool includes 142 varieties of cultivated species and relatives of citrus fruits: C. medica L; C. reticulate Blan.; C. lemon Burm; C. paradise Macf; C. maxima Burm; C. sinensis Osb; C. aurantium L.; C. reshni Tan.; Fortunella SW; C. trifoliate Raf.; C. icchangensis Swi.; C. × insitorum Mabb.; C. hystrix DC, etc. The collection was analyzed and 19 valuable sources of economically significant traits with increased sensitivity to regional stressors were identified. The selected sources are included in a selective process in order to synthesize new genotypes with improved significant properties. 45 crossing combinations were carried out, 28 promising forms of different directions were isolated from the environment of hybrids. Early-ripening (II decade of october), mid-season (I decade of november), late-ripening (II-III decade of december) genotypes have been bred, undersized (1.5-2.5 m) forms have been identified. Forms were identified as candidates for varieties with a good yield from 5.0 to 5.6 kg/tree. Samples for ornamental gardening are presented: C. × bergamia, C. × bergamia var. Melarosa, C. × limetta, C. × limonelloides, C. × aurantium myrtifolia Cinotto are also hybrid forms 209-1; 2002-1; Ш18-sp.

The molecular identification of valuable genotypes is an important problem of germplasm management. In this study, we evaluated the potential of 11 universal primer pairs for the DNA barcoding of locally derived cultivars of subtropical crops (actinidia, feijoa, citrus, and tea). A total of 47 accessions (elite cultivars, forms, and breeding lines) of these four genera were included in the study. The efficiency of the following universal primers was assessed using Sanger sequencing: ITS-p5/ITS-u4, ITS-p5/ITS-u2, ITS-p3/ITS-u4, 23S,4.5S&5S, 16S, petB/petD, rpl23/rpl2.l, rpl2 intron, rpoC1 intron, trnK intron, and trnE-UUC/trnT-GUU. Among these primers, trnE-UUC/trnT-GUU showed greater intraspecific polymorphisms, while rpl2 intron and 16S displayed the lowest polymorphism levels in all crops. In addition, the 23S,4.5S & 5S, and rpoC1 intron were efficient for intraspecific analysis of tea and actinidia species. Using five efficient chloroplast primers, a total of 22/6 SNPs/InDels were observed in tea accessions, 45/17 SNPs/InDels in actinidia, 23/3 SNPs/InDels in mandarins, and 5/4 SNPs/InDels in feijoa. These results will be useful for the further development of DNA barcodes of related accessions.

The component composition of the essential oil of the leaves of three types of rare citrus fruits from the collection of the Federal Research Center "Subtropical Scientific Center of the Russian Academy of Sciences" has been determined. The purpose was to study the volatile organic substances that make up the essential oil. It will not only optimize the growing conditions under which the accumulation of components will be maximum, but also to conduct targeted selection. Essential oil is extracted from the leaves of three citrus species: C. ichagensis Sw., C. maxima ‘Sambokan’ (pompelmus), C. maxima ‘Gulripshsky' (pompelmus) and hybrid C. paradisi G-A-1 (grapefruit). The studied components of the essential oil were transferred from the leaves of citrus plants to the gas phase by heating the crushed suspension with vibrational stirring in a closed volume in the presence of water. Identification and evaluation of the relative content of chemical compounds of the vapor-gas phase was carried out by gas chromatography-mass spectrometry. More than two dozen components have been identified using the mass spectrum database, mainly from the classes of mono-, bicyclic terpenes and sesquiterpenes. The leading component of essential oil in the leaves of S. maxima ‘Gulripshsky’, S. maxima ‘Sambokan’ and C. ichagensis Sw. is γ-terpinene, while in the leaves of C. paradisi the main component was D-Limonene. The species specificity of the chemical composition of the essential oil of C. maxima, C. paradisi and C. ichangensis Sw. was noted. The results obtained will be used to determine the species specificity of essential oils of promising types/ forms of various citrus fruits and applied in further breeding work to obtain varieties / forms with the highest content of essential oil.

The Federal Research Centre, the Subtropical Scientific Centre of the Russian Academy of Sciences (FRC SSC of RAS), maintains and sustains a unique collection of citrus crops, comprising 144 varieties collected from different geographical zones. The collection serves as a foundation for breeding work aimed at developing new varieties adapted to the extreme conditions of the humid subtropics in Russia. The breeding focus is on early-ripening, high-yielding, large-fruited citrus varieties with high fruit quality parameters. An extensive hybrid pool has been created, with the study of 165 forms of citrus from various origins, of which 60 are identified as promising and 28 as elite. Through comprehensive evaluation of elite forms, early-ripening and large-fruited forms have been identified, characterized by good yields and high fruit quality characteristics. Early-ripening hybrids of C. reticulāta 02-1, 2-5, and 2-2; 01-04; 01-4 ripen in the second decade of October. Promising forms of C. paradīsi G-A-2 and G-A-1, characterized by large fruit size ranging from 240.1 to 345.1 g, have been selected. The largest fruits are observed in C. Bergamia 16; P-22, with an average weight ranging from 350.8 to 430.40 g. High vitamin C content is noted in forms of C. paradīsi G-A-1; G-A-2 (54.1-43.7 mg/100g) and C. maxima P-20 (42.3 mg/100g). The sweetest fruits are found in the form of C. Bergamia 16, with a sugar content of 255.94 g/liter. The selected forms hold significant value for further breeding research.