Growth of Paulownia ssp. Interspecific Hybrid 'Oxytree' Micropropagated Nursery Plants under the Influence of Plant-Growth Regulators

The aim of the study was to examine the effects of application of plant-growth regulators (PGR) on the growth of paulownia plants and evaluate their usefulness in paulownia nurseries. The experiment was carried out on the paulownia interspecific hybrid (Paulownia elongata x Paulownia fortunei) 'Oxytree'. Micropropagated plants grown in pots were sprayed with PGR solutions. Gibberellins (GA(3), GA(4)+GA(7)), 6-benzyladenine (BA), triclopyr (TPA), ethephon (ETH), daminozide (DA), prohexadione-Ca (PH), and trinexapac-ethyl (TE) were used. They were included in commercial products (Florgib 245 mg dm(-3), Gibb plus 11 SL 5 cm(3) dm(-3), Globaryll 100 SL 1.5 cm(3) dm(-3), Topper 10 ST 200 mg dm(-3), Agrostym 480 SL 2 cm(3) dm(-3), B-Nine 85 SG 2 g dm(-3), Regalis plus 10 WG 2.5 g dm(-3), Moddus 250 EC 1 cm(3) dm(-3), respectively). None of the studied preparations modified positive correlations between the longitudinal vs. transverse growth of stems and growth of leaves. Not only GA(3), GA(4)+GA(7), but also BA (cytokinin) and unexpectedly TE (retardant) stimulated stem elongation and thickening. Furthermore, the effect of TE lasted longer than influence of GA(x) and BA. Leaves of TE-treated plants were distinguished by a higher chlorophyll a/b ratio, and a lower relative chlorophyll content and efficiency of photosystem II (F-v/F-m, F-v/F-0). TPA strongly deformed the stems and leaves of liners. Other regulators (ETH, DA, PH) retarded the diameter growth of stems and leaf expansion. Some results obtained by GA(x), BA, and especially by TE treatment, might be beneficial for paulownia grown as ornamental and/or timber tree.