Features of the female gametophyte formation in a columnar apple variety for breeding at the polyploid level

Abstract

The article discusses the features of the development of the female gametophyte in the columnar apple cultivar ‘Vostorg’ as the initial maternal form for breeding at the polyploidy level. The inclusion of columnar apple cultivars in heteroploid crosses is promising, as it will allow to obtain cultivars combining the positive qualities of triploids (annual fruiting, high fruit quality) and the advantage of columnar shapes (compact tree habit and earlier onset of fruiting). The quality of the gametes and, as a result, the positive hybridization and the ploidy of the offspring depend on the features of the embryonic structures. In the columnar winter apple cultivar ‘Vostorg’, the anatropic crassinucellate double-integumentary ovules are formed in spring, in which the germinal sacs develop. In the buds with petals extended by half, there are undifferentiated germ sacs with three cells of the egg apparatus at the micropillary end and three antipodes at the chalazal end of the germ sac; two polar nuclei are in the center of the germ sac. There is asynchrony in the formation of the female gametophyte, a multicellular archesporial complex (5-20 cells), and additional tetrads next to the developing germ sac. Several cases of formation of germinal sacs located side by side parallel to each other have been noted. Anomalies in the structure of the germ sac have been revealed: differentiation of all cells of the egg apparatus according to the type of synergides, the presence of two egg cells and one synergide. After flowering (4-5 days), two- and three-celled embryos were present in the germ sac. The average yield of triploid hybrid seedlings with the participation of the columnar apple ‘Vostorg’ was 67.9%. This cultivar is recommended as a maternal parent for heterochromosomal crosses.