Seed quality and germination characteristics of Begonia grandis in protected ground conditions

The aim of the study was to investigate the characteristics of seed propagation of Begonia grandis Dryand. in protected ground conditions and artificial pollination in Siberia. Five genetically independent plants that were not descendants of the same clone were used in the experiments. To determine the seedification coefficient, an original method of accounting for developed microscopic seeds and aborted ovules using microphotographs was used; this indicator varies within 33–66 %. Four fractions of seeds were distinguished by their completeness: complete; complete with minor deviations; poorly complete (folded); uncompleted. Normally developed embryos are found in the first two fractions of seeds; they are oblongoval, large relative to the size of the seed: (306 ± 8) μm in length, (152 ± 5) μm in width. The seeds of B. grandis have the sizes of (423 ± 5)–(435 ± 5) μm, (218 ± 6)–(237 ± 3) μm, respectively, and are embryonic: they are characterized by an extremely low reserve of nutrients and a poorly expressed diffuse endosperm. The morphological features of the seedlings have been clarified. It has been established that the seeds begin to germinate on the 5th day. On the 14th day, the germination reaches a plateau and is 54–78 %. The sprouts have unique growth potential: the hypocotyl is the most developed and the first to start growing, then the root hairs are formed, at the next stage the seed coat is shed and the cotyledons straighten out. It was established for the first time that the formation of the growth cone in B. grandis begins after the sprouts have started photosynthetic activity. The cotyledon rudiments serve, due to their small size, only for photosynthesis. Due to the extremely small supply of nutrients in the seeds, the life of the sprout depends on the fastest possible transition to autonomous nutrition. The adaptive devices for such a rapid transition are the absence of a visually diagnosable plumule and the early development of root hairs at the initial stages of germination.