OPEN ACCESS
NFM, Volume 40: 43–57.
Original scientific paper
https://doi.org/10.5552/nms.2019.5

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Abstract

By selecting plus trees in a base population, a breeding process of Norway spruce as Christmas trees was initiated in Croatia. The next stage of the process is the optimization of the cloning procedure of selected plus trees for the mass production of their reproductive material (seedlings). The assumption is that qualitative reproductive material exhibiting stability of targeted phenotypic traits will be created in such a way.

The main aim of the research was to determine the success of various hormonal treatments on rotting of hardwood cuttings of older Norway spruce trees (10–12 years). Two experiments were carried out. In the first, 270 cuttings were cut off in early spring from each of the three crown levels (upper, middle and lower third of a crown), on a sample of 10 trees. The cuttings from each level were treated with 24 different treatments (dipped in IBA and NAA hormone solutions of 250, 500, 2500 and 5000 ppm for 10s, 1h and 2h). In addition to these treatments, 10 cuttings from each crown level were treated with a commercial hormone product named Clonex (a gel). Additional 10 cuttings were treated with distilled water for 2h and the remaining 10 were not treated. The last two groups of cuttings served as a control of the success of the analyzed hormonal treatments. Another study was conducted on 80 cuttings cut off in late fall from the lower third of a crown of the 13 selected plus trees. Thirty cuttings were treated for 10s with: (i) 2500 ppm IBA solution, and (ii) 500 ppm IBA solution. The remaining 20 cuttings served as the control. Afterwards, the cuttings were placed in containers filled with peat, sand and perlite substrate. The rooting success, the number of roots per cutting, and the length of the longest developed root were determined later in October.

The results showed that, on average, spruce trees at the age of 10+ years could be relatively successfully cloned (50% rooted cuttings on average) by rooting hardwood cuttings taken in late autumn or early spring from the lower third of a tree crown, without any treatment. The percentage of rooted cuttings and the quality of newly created roots can be improved at low cost and high effectiveness by treating cuttings with distilled water for 2 hours. However, the results indicated that by treating the base of cuttings taken in early spring with a hormonal solution of 500 ppm IBA for 10s, the percentage of successful rooting could be significantly increased (up to an average of 80% rooting). Hardwood cuttings taken from the lower third of crowns were most successfully rooted, even without any treatment (50% control cuttings, compared to 40% control cuttings from the middle and 20% rooted cuttings from the top third of crowns). The results also indicated marked individual differences in the success of rooting of cuttings taken from the lower parts of a crown (percentage of rooting ranged from 0% to 100%).

Key words: Christmas trees, breeding, plus trees, cloning, genotypes, IBA, NAA