The performance and rooting of eucalyptus grandis x nitens cuttings.

Abstract

Hybrid clones of Eucalyptus grandis and E. nitens (GN) have consistently been shown to be suitable for planting in cold, dry, marginal plantation sites, where they exhibit high yields and superior pulp properties. However, their clonal propagation is hindered by the very poor rooting success of cuttings. The present study aimed at assessing the effect of cutting type, time of year of setting cuttings and Seradix 2 application on rooting and development of cuttings of a commercially important Eucalyptus grandis x Eucalyptus nitens clone (GN107). Cuttings were prepared from clonal hedge coppice at the Mondi Business Paper, Trahar Technology Centre, Hilton. Three cutting types were used (cut at different distances from the node) for each terminal (situated below the apical bud) and non-terminal cuttings. The leaves were trimmed and, for half the cuttings, the base of the stem of cuttings were dipped in Seradix 2 rooting powder (3 g kg-1 4-(indole-3-yl)-butyric acid (IBA). They were then placed into rooting trays (128 inserts/ tray arranged as 8 rows x 16 columns). Seradix 2-treated and Seradix 2-untreated terminal and non-terminal cuttings, cut at, above and below the node (twelve treatments in total) were set in trays with one treatment per column of eight replicates, per tray. There were nineteen trays overall. The trays were filled with peat, perlite and vermiculite (3:3:1) and were maintained in a Mondi greenhouse, with air temperature at 25°C to 27°C (thermostatically activated fans), root zone temperature at 28°C (bed heaters) and 20 second misting at 10 minute intervals (automatic misters). The study was carried out in November 2005, April 2006 and June 2006. In the first experiment, both terminal and non-terminal cuttings were used; thereafter only non-terminal cuttings were used. The plantlet yield was very low, regardless of cutting type, Seradix 2 treatment and the time of year the cuttings were set. The highest plantlet production (12.5%) and rooting frequencies (13.8%) were achieved with non-terminal cuttings treated with Seradix 2. Although not statistically significant, Seradix 2 inhibited shoot production (31.4% for Seradix 2-untreated and 24.2% for treated cuttings). The position at which inserts were cut in relation to the node did not significantly affect the number of plantlets produced and non-terminal cuttings appeared hardier and performed better than terminal cuttings. The time of year of setting cuttings did not have any significant effect on plantlet yield, nonetheless, plantlet yield was highest in cuttings set in November (9.2%) and lowest in April (0.4%). In addition, cuttings set in November (spring), had superior shoot development in terms of the number of cuttings that produced shoots (regardless of root production), shoot length and the mass of shoots relative to root mass. The highest percentages of cuttings that produced roots (regardless of shoot growth) (10%) and the highest number of roots per cutting (2) were part of the June trial. Therefore, cuttings set in June (winter) had superior root development as compared with cuttings set in November (spring) or April (autumn). In all of the studies, three rooting patterns were observed in cuttings: roots produced only from the cut area only (type 1), only from the sides of the stem (type 2) and from both sites (type 3). Non-terminal cuttings treated with Seradix 2 showed a higher incidence of types 2 and 3 rooting patterns than the terminal cuttings. Seradix 2 application increased the prevalence of types 2 and 3 rooting patterns. Although not statistically different, cuttings dipped 2.5 cm into Seradix 2 produced more types 2 and 3 rooting patterns than cuttings dipped at the abaxial end only. Light microscopy of stem sections of cuttings indicated that roots appeared to originate from the xylem archs as well as from the cambium. The collected data indicate that it is necessary to continue research towards improving the efficiency of plantlet production of GN107 via cuttings. It appears that cuttings of this clone may be set throughout the year and that terminal cuttings should be avoided. In addition, the present practice at the Mondi Hilton nursery of treating cuttings with Seradix 2 needs to be reconsidered as although it increases rooting, it does not increase plantlet production due to its apparent inhibitory effect on shoot development.