In Vitro Propagation of Commercially Used Krymsk 5® (Prunus fruticosa × Prunus lannesiana) Cherry Rootstock: Impact of Sugar Types and pH Levels

Abstract

In the present study, the effects of different types of sugars and cultivation medium pH levels on the micropropagation of Krymsk 5® cherry rootstock were investigated. During the proliferation stage, the effects of four sugars (sucrose, fructose, glucose, and sorbitol) both separately and in two combinations were studied, along with the effects of pre-adjusted pH (4.5, 5.0, 5.2, 5.5, 5.8, 6.0, 6.2, or 6.5) on shoot proliferation parameters, growth medium’s post-autoclaving and post-cultivation pH, and their relations. Similarly, during the rooting stage, the effects of four sugars (sucrose, glucose, fructose, or sorbitol) at three concentrations (1% w/w, 2% w/w, or 3% w/w) without any auxin inclusion were studied as well as the effects of two sugars (sucrose or fructose) at six pre-adjusted pH levels (4.8, 5.2, 5.8, 6.2, or 6.5), also in the absence of auxin, on rooting parameters. Explants cultivated in fructose-supplemented growth mediums exhibited superior proliferation performance, characterized by the highest values of shoots per explant, shoot length, and nodes per explant. Generally, the medium’s pH decreased after autoclaving, and proliferation performance was favored by low pH values (either pre-adjusted or post-autoclaving). As far as rooting is concerned, fructose inclusion induced a higher rooting percentage (88%) compared to sucrose. The highest rooting was obtained in fructose-supplemented rooting mediums at concentrations of 2% or 3% w/w (95% rooting in both cases), in the absence of auxins. Post-autoclaving pH in fructose-supplemented rooting mediums was lower and buffered in low pH levels than in sucrose-supplemented ones, and the rooting of explants in all pH combinations with fructose exceeded 75%. In addition, rooting was negatively correlated with the post-autoclaving pH. These findings underscore the significance of both the sugar type and the post-autoclaving pH of the medium in both proliferation and rooting stages, highlighting their possible physiological, biochemical, or hormonal effects. Additionally, rooting without the use of auxin, but with the correct choice of sugar, emerges with both financial and environmental benefits, whereas fructose could be potentially used as a buffering agent.