Improving production efficiency is a major challenge for modern orchard systems. The primary response in horticulture is to develop high-density orchard systems that use dwarfing rootstocks and intense management strategies to maintain small tree size. As development and evaluation of novel orchard systems may help improve understanding of plant physiology for the development of high-density systems. The effect of tree size and architecture on physiological and production efficiency was evaluated for tart cherry (Prunus cerasus, P. mahaleb) and apple (Malus spp.) orchard systems using a physiologically driven modeling approach, called allometry. Branch dimensions, canopy dimensions and biomass were measured for 24-year-old tart cherry individuals and 10-year-old 'Golden Delicious' apple individuals on various rootstocks in experimental blocks at the Kaysville Research Farm in Davis Co., Utah. Tree size was related to annual fruit biomass that had been collected over the duration of the apple trial. Branch dimensions, canopy dimensions, yield, and fruit quality were collected in commercial tart cherry orchards of Utah Co. Tree size, architecture, and biomass of tart cherry and apple expressed strong allometric relationships that were broadly consistent among the two orchard tree species and the theoretical expectations derived from wild plants. The most consistent relationship was the trunk diameter (or trunk cross sectional area) - stem biomass relationship, which broadly followed the 8/3-power law. Branch and canopy dimensions that include a measure of length, such as branch length and canopy height, demonstrated architecture indicative of high water efficiency and metabolic activity that is relieved from biomechanical constrains of weight bearing. The apple rootstocks differed from each other in production efficiency with individuals that express smaller branch and canopy dimensions producing a higher proportion of fruit relative to tree size. In the commercial tart cherry orchards, smaller individuals with relatively higher canopy height and spread expressed higher yield and fruit quality. Overall, this research supported the continued development of training systems that maintain small trees to improve physiological and production efficiency. Further research must reconcile other consequences of intense management and overproduction that arise with the increased efficiency facilitated by small tree size and high-density orchard systems to maintain sustainable fruit production.

Presented thesis evaluates the risk of ongoing hybridization (antropohybridization) in highly endangered Prunus fruticosa in the Czech Republic and selected adjacent countries. Absolute genome size analysis (estimated by flow cytometry) combined with both numeric and geometric morphometrics were used for evaluation of hybridization. Prunus fruticosa frequently hybridize with naturalized Prunus cerasus (emerging tetraploid hybrid Prunus ×eminens) and native Prunus avium (forming triploid hybrid Prunus ×mohacsyana). Discrimination between P. ×eminens and P. ×mohacsyana is difficult, when using leaf morphology characters only, so the occurrence of triploid hybrids was strongly underestimated in the Czech Republic (only tetraploid hybrids were reported). Both hybrids are surely differentiated using flow cytometry analysis (based on different ploidy level). The majority of analyzed populations is formed by either individuals of pure P. fruticosa or one of the mentioned hybrids. Only four populations were mixed. Continuous variability in absolute genome size was found in two of them, which may indicate hybrid swarm forming (incl. primary hybrids and backcrosses). Our findings can be considered only as indirect evidence for introgression, which needs to be confirmed by molecular markers (for example...