Assessment of the Effect of Treating ‘GiSelA 5’ Softwood Cuttings with Biostimulants and Synthetic Auxin on Their Root Formation and Some of Their Physiological Parameters

The ‘GiSelA 5’ rootstock is of high importance for growing sweet cherries because it significantly reduces the growth vigour of the trees and accelerates their fruiting. However, the method of its propagation using ‘in vitro’ cultures is expensive, prompting researchers to look for alternative methods of propagation. One of these is the root formation in shoot cuttings. The experiment presented in this paper compared the use of powdered synthetic auxins (Rhizopon AA, Ukorzeniacz AB) and their alcoholic solution (IAA, IBA), and the biostimulants Goteo and Bispeed as foliar sprays for root formation in softwood cuttings ‘GiSelA 5’ and measured some parameters of physiological processes. In addition, two different substrates of river sand with peat (1:2) and peat substrate with perlite (2:1) were used. Cuttings were obtained on two dates, in the first and third years in the month of June. Biostimulants increased the number of rooted cuttings (Goteo—16.1%, Bispeed—18.1%) without improving their growth and the intensity of most of the analyzed physiological processes compared to the control. Synthetic preparations also increased the percentage of rooted cuttings Rhizopon AA (24.4%), Ukorzeniacz AB (21.4%), auxin IBA (19.7%) and auxin IAA (14.7%), while simultaneously improving their growth and level of vital processes compared to the controls and biostimulants. The substrate consisting of peat with sand improved root formation by 6.2%, without significantly changing the growth parameters and vital functions of the cuttings. The earlier date of propagation increased the root formation percentage only by 4% and the number of roots by 14% of the ‘GiSelA 5’ rootstock cuttings.