Professional paper
https://doi.org/10.31298/sl.142.5-6.2
Propagation of paulownia by root cuttings
Damir Drvodelić
orcid.org/0000-0003-1948-0692
; Šumarski fakultet Sveučilišta u Zagrebu, Zavod za ekologiju i uzgajanje šuma,
Abstract
The genus Paulownia, family Paulowniaceae, contains about nine species and several natural hybrids which are native to China. Some important species in this genus include P. albiflora, P. australis, P. catalpifolia, P. elongata, P. fargesii, P. fortunei, P. kawakamii and P. tomentosa. More recently, numerous hybrids have been obtained by hybridisation for the purpose of increasing the rate of growth and increment, as well as develop resistance to low temperatures. In Croatia, the most commonly propagated are the Paulownia hybrids Shan Tong and 9501, although there are also other hybrids obtained by selections in some “in vitro” laboratory. The goal of this article is to explore different propagation methods of Paulownia in the nature, the problem of its invasiveness and nursery propagation by means of autovegetative macropropagation method from root cuttings. There are three phases of rooting the cuttings: initiation, induction and expression. There is direct and indirect induction. The most sensitive moment is the connecting of the conductive elements of small roots with parts of a cell. The success of root development on the cutting depends on the physiological status of the parent plant, sugar quantity, auxin metabolism, mineral nutrition, phenol metabolism and others. There are four stages
of Paulownia propagation from root cuttings: digging out and finishing of root cuttings from the parent stock, pricking out the cuttings into plastic containers filled with potting media, rooting the cuttings and the establishment of a new parent stocks. The Paulownia root cuttings Shang Tong and 9501 were taken with regard to the polarity in the following way; the bottom (distal) part of the root was cut at an angle of 45 degrees and the upper (proximal) part was cut at an angle of 90 degrees. The cuttings were divided into short (8 cm) and long (15 cm) cuttings. Each group of the cuttings was additionally divided into thin and thick cuttings, making the difference visible to the naked eye. A total of 15 cuttings were taken from each group for the purpose of our research. In the experiment, one part of the cuttings was pricked out in a heated greenhouse 7 days after root excavation and the other part of the cuttings was pricked out after drying at room temperature in the plant growth chamber. The first group of 60 cuttings was taken on December 14th and pricked out in perforated 5.0 l plastic bags filled with ready-made Klasman Steckmedium rooting medium. The rooting medium was enriched with 3g/l of Osmocote Exact Standard 5-6M formulation 15-9-12+2MgO+TE, the 3rd generation of controlled release fertilizers. The cuttings were not treated with a phytohormone or rot prevention fungicides. The cuttings were pricked out in such a way that the upper surface of the cut at 90 degrees was at the level of the potting medium. The second group of 60 cuttings was dried in the Kambić RK-980 CH growth chamber. The chamber temperature was 21 °C and the relative air humidity was 40%, which equalled storage of the cuttings under constant room conditions. The cuttings were kept in the growth chamber for 5 days. Pricking out was performed on December 12th, 2017 in the same way as the first group of cuttings. The first rooting registration was done on February 19th, 2018, which in the case of the first group means 67 days after pricking out and for the second group 60 days after pricking out. Drying the Paulownia Shang Tong hybrid cuttings increased the rooting success in all the variants, and was particularly evident in thick cuttings 8 cm long and thick cuttings 15 cm long. Selecting thicker cuttings and drying them at room temperature for 5 days can be recommended because this procedure yields a significantly higher rooting percentage. Excessive moisture in the potting medium used for the Paulownia root cuttings negatively affects root system development. It was also confirmed that drying the Paulownia hybrid 9501 cuttings increases the rooting success in all the variants, with the exception of thin cuttings 8 cm long, where the rooting percentage was the same (33 %). Thick cuttings 8 cm long present a particularly interesting case, where not one single cutting which was not dried took root, while as many as 80 % of cuttings took root after being dried. Taking thicker cuttings of the Paulownia 9501 hybrid and drying them at room temperature for 5 days can be recommended, because this procedure yields a significantly higher rooting percentage. The rooting percentage of cuttings without drying would certainly be higher if the cuttings had been taken immediately after the root system was dug out with a dredge, as recommended in practice. In this case, the minimal air temperatures of -4 °C and -5.6 °C caused the root system to freeze. The average minimal air temperature in the period from December 8th to December 14th was only 0.8 °C. When the root is frozen, the bark is separated from the wood manually, and such cuttings either decay or sprouting from the lower adventitious buds. The root cuttings of the Paulownia hybrids Shan Tong and 9501 should be taken immediately after the root system of the parent plant is dug out, while the average air temperature should be above 0 °C. Our studies confirmed the harmful effect of temperatures from -4 °C and -5.6 °C on root cuttings, as such temperatures caused the cuttings to freeze. The best calendar period for digging out root cuttings, depending on the year, should be in March. It was confirmed that the root cuttings of Paulownia hybrid 9501 can also be rooted in ordinary water under controlled conditions (no light, constant temperature of 20 °C). The cuttings were placed in “in vitro” Snijders Scientific B.V., ECD01E germination table on December 21st, 2017, and were photographed on February 21st, 2018, or 62 days after being placed in the water.
Keywords
Paulownia Shan Tong; Paulownia 9501; nursery production; propagation phases; rooting cuttings
Hrčak ID:
202363
URI
Publication date:
30.6.2018.
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