The Pivotal Role of Phenological Stages Enhanced by Plant Origin Preparations in the Process of Rhizogenesis of Rosa ‘Hurdal’ Stem Cuttings

Abstract

Some biostimulants, including plant origin preparations, act similarly to plant growth regulators. Moreover, the supplementation of known and unknown rooting cofactors can stimulate rhizogenesis in cuttings. The aim of this research was to assess the response of difficult-to-root and long-rooting stem cuttings of the once-blooming old variety Rosa ‘Hurdal’ to preparations of plant origin. The hypothesis was that the plant origin preparations could enhance rooting processes by inhibiting chlorophyll a/b degradation in leaves and postponing leaf senescence, simultaneously increasing the quality of cuttings. The one-bud stem cuttings were made in four phenological stages: (H1) flower buds closed, (H2) open flowers, (H3) just after petal fall, and (H4) 7–14 days after petal shedding. They were treated with either standard commercial powder preparations containing 0.4% indole-3-butyric acid (IBA) or 0.2% 1-naphthalene acetic acid (NAA) as well as with commercial plant origin preparations that this work will henceforth refer to as: Algae Extract, Organic Preparation, and Plant Extract. The cuttings were evaluated after 12 weeks of rooting them in two substrates: peat–perlite and peat–sand (v:v; 1:1). Mean root percentages for both substrates were noted after preparation from stage H1 (74.5%), H2 (59.5%), H3 (50.8%) shoots. The H4 cuttings did not root at all and were not considered further. The means for all phenology stages together were the highest by the use of 0.6% Algae Extract, 0.012% and 0.02% Organic Preparation, and 0.2% and 0.4% Plant Extract. The lowest means were reported for the control cuttings as well as NAA and IBA treatment. Plant origin preparations encouraged growth parameters but did not unequivocally inhibit the decrease of chlorophyll content in the cuttings’ leaves. The percentage of cuttings that rooted in both rooting substrates was determined by the quality of the cuttings as well as the chlorophyll a/b and soluble protein content in the leaves.