Characteristics of microsporogenesis in the triploid apple tree and it’s parental form in connection with usage in breeding at the polyploid level

Abstract

An effective method of creating triploid apple cultivars, which are superior in their characteristics to diploid cultivars, is the crossing of heterochromosomal forms of the type: 2x×4x, 4x×2x. In order to provide a wide range of genetic diversity of riploid hybrids, it is necessary to have a large set of tetraploid donor forms of diploid gametes. A limited set of such forms is a limiting factor for this direction of breeding. And the effectiveness of work on obtaining new valuable apple varieties based on the use of the polyploidy method largely depends on their diversity Therefore, the identification of new apple tetraploids, as well as the study of cytoembryological features of their generative structures, the determination of the quality of the formed gametes necessary for successful breeding and for predicting the results of these works are relevant. Meiosis during microsporogenesis was studied in two tetraploid apple forms. To study meiosis during microsporogenesis, temporary pressed specimen were prepared by the acetohematoxylin method; the propionic-lacmoid method was used to determine the ploidy of hybrid offspring. Microscopic studies were carried out on a Nikon-50i microscope at a magnification of 10 x 105 x 40, 10 x 1.5 x 100. The analysis of the course of meiosis during microsporogenesis in apple tetraploid 34-21-39 [30-47-88(4x)×Krasa Sverdlovska(2x)] and its parent form 30-47-88 [Liberty×13-6-106 (Suvorovetz seedling)] showed that the hybrid 34-21-39 was characterized by the most correct course of meiosis. The largest percentage of deviations and the diversity of morphological types of disorders were detected in the form 30-47-88. Common types of violations were noted. Despite the presence of disorders during meiosis in tetraploid forms, microsporogenesis ended with the formation of visually normal one–dimensional pollen: 89% in the form 34-21-39 and 50% in the form 30-47-88. In combinations of crosses involving the studied forms, a high yield of triploid plants was noted. Consequently, the tetraploid apple forms 34-21-39 and 30-47-88 can be recommended for hybridization for the purpose of mass production of triploid seedlings. The results allow us to conclude that the tetraploid apple forms 34-21-39 and 30-47-88 can be used in breeding as pollinators in heteroploid crosses (2x×4x) to obtain triploid genotypes.