Behaviour of Micropropagated Own-Rooted Trees of Plum Cv. Stanley in the Orchard. 2. Reproductive Behaviour

Own-rooted micropropagated plants of plum cv. Stanley, grown further for a single year in the nursery, were planted for comparison with trees, traditionally produced by grafting on clonal (GF655/2 - produced by micropropagation) and seedling (Dzhanka 4 - Prunus cerasifera Ehrh) rootstocks. In vitro plants of the same cultivar, grown further in the nursery for two vegetation periods, were also involved in the study. The following more important traits were observed: trunk cross-sectional area, crown volume and projection area, total and mean annual increment, as well as the first order branching angle. The objective of the study was to establish the growth characteristics of in vitro-produced plants of plum cv. Stanley, grown further for a single year, from their juvenile period to full bearing initiation. During the study years, the trunk cross-sectional area was largest in the control variant, budded on Dzhanka 4 seedling rootstock. The values of trunk thickening in the rapidly produced own-rooted trees were insignificantly higher than those of the trees that were further grown for two years, the difference between them being significant only during the second year after planting in the orchard. After the third vegetation, in spite of the different absolute values of this trait, no significant difference was found among the three aforementioned variants. The lowest increment was established for the trunk, the crown volume and area of trees budded on the clonal rootstock GF 655/2. The difference was significant both by value and statistically. The same regularity was established for the total annual trunk growth in length and thickness. An exception was observed during the second vegetation period when the variant produced rapidly surpassed significantly all other variants. The branching angle was larger in the in vitro-produced plants and particularly in those obtained by rapid production.