Seed productivity of alloplasmic lines of Beta patula and B. maritima with sterile cytoplasm under the conditions of apozygotic reproduction

Purpose. Revealing the effect of the cytoplasmic genome of replaced lines with the plasma of wild species Beta patula and B. maritima L., and apozygotic lines A4–A8 with the cytoplasm of S vulgaris Owen on the main factors of apozygotic reproduction, seed productivity, germination, monogermity and sterility as affected by the genetic origin of breeding material. 
Methods. The research was carried out in the Cytogenetics Laboratory (IBCSB), the Laboratory for Apomixis and Polyploidy of the Yaltushkiv EBS, and the Laboratory for Adaptive Breeding (Veselyi Podil EBS). Apozygotic seeds were obtained under a pollen-free regime according to the IBCSB’s Methods for Spatial Isolation and Parchment Insulators. Each seed bearer plant phenotype was determined during the flowering period by pollen sterility and partial flowering. Classification of plants was performed according to Owen (1945), with identifying plants of CMS-0, Type CMS-1, and CMS-2 types. The Monogermity of seed plants was assessed visually by the presence of separate fruits on the central shoots. In 2021, the roots of the replaced lines of the Veselyi Podil EBS were planted under the conditions of a pollen-free regime in the experimental field of the IBCSB. Seed production under apozygositic conditions was studied, taking into account the number of set fruits per 10-cm segment with 5 replications for each seed bearer. Germination was determined on the 10th day and germination vigour on the 5th day. 
Results. New sources of cytoplasmic male sterility (CMS) were obtained in the cytogenetics laboratory based on a genetic model of crossbreeding analysis, using differentiation and tools according to the marker-linked genes of hypocotyl color R+r-, and one / two-year development cycle B+b-. The analyzers for the nature of sugar beet sterility were sterility maintainers, dominant homozygotes for recessive genes of anthocyanin color, development cycle, partial fertility and sterility (NBeta vulgaris Sxxzz rr bb). Monogerm pollen-sterile lines with an apomictic way of seed reproduction (Yaltushkiv EBS) (A4–A8 Beta vulgaris Sxxzz rr), selected for the dominant color of the hypocotyl R+r-, stabilized for the trait of monogermity, 100% sterility and 2x gene ploidy, were characterized by low seed productivity. High rates of apozygotic seed development (80 to 96.4% of the number of set flowers) were observed against the background of the sterile cytoplasm of Beta maritima (Turkey). In the CMS BC4S patula line, the number of set apozygotic seeds ranges from 34 ± 0.3 to 39 ± 0.42, and the indicators of degenerated flowers under apozygotic regime varied from 31.2 to 54.3%. Isolated were seed plants with high self-reproduction, such as BC4S maritima Turkey, k.2/1, k.6/2, k.6/3 and k.3/4, k.9/4 on the background of new plasma of wild species of B. patula. The phenomenon of high self-reproduction of seeds (up to 98.5−96.4% of set flowers) was detected in line 21-011 CHS BC5S patula, which was comparable with hybrids and sterility maintainers (97.5−93.1%), which is determined by a special interaction of the beet nuclear genome of sugar beet and new plasma of wild species of the genus Beta L. 
Conclusions. The apomictic way of seed reproduction ensures the shortening of the breeding scheme for sugar beet due to high seed reproduction of mother parent in substituted lines with new plasma and differentiation by gametophytic reduction of parthenogenesis using morphological marker traits.