Thesis (Ph. D.)--University of Tasmania, 1999. / Includes bibliographical references.

The objective of this study was to develop and implement an advanced generation breeding programme at the Institute for Commercial Forestry Research (ICFR) to manage and integrate the many and disjunct breeding and production populations of Eucalyptus nitens established by various entities over the past 30 years at multiple sites in South Africa. To develop such a breeding strategy, a good understanding of the population genetics, and the underlying assumptions made by tree breeders about the species, was needed. Eucalyptus nitens is an important forestry species grown for pulp and paper production in the temperate, summer rainfall regions of South Africa. A tree improvement programme has been ongoing at the ICFR for three decades. The measurement and statistical analysis of data from eight F1 trials established during the 1980s and 1990s have enabled characterisation of the ICFR’s breeding population. Provenance testing showed that the more northerly New South Wales (Australia) Eucalyptus nitens provenances of Barren Mountain and Barrington Tops are distinctly better suited to growth in South Africa than the southern New South Wales provenances and the Victorian provenances, Penny Saddle and Bendoc. Generally, the species was not badly affected by Coniothyrium canker. High Type B genetic correlations for all sites pairs, except one comparison, ranged from 0.75 to 0.99 for diameter at breast height at 76 to 113 months, indicating very little, or no, genotype by environment interaction for diameter at breast height for the genotypes tested in the F1 generation. Narrow sense heritability estimates ranged from 0.01 to 0.34, indicating that the species provides a breeding opportunity for improvement of diameter growth. High genetic correlations of greater than 0.90 between diameter measurements at 52 to 62 months after establishment and diameter measurements at 94 or 113 months were found, indicating that selections can be made reliably at five or six years. Diameter measurements at both 60 months and full rotation (94 to 113 months) were highly correlated with the final height measurements in these trial series (rg > 0.71 and > 0.83, respectively). Predicted genetic gains for the F2 over the F1 generation were highest in the trials at Goedehoop and Arthur’s Seat, with predicted increases in diameter at breast height of 3.07 cm (17.1%) and 3.17 cm (20.7%), respectively, at full rotation. Genetic improvement in the species has been slower than anticipated due to delayed and infrequent flowering and seed production. Three genetic gain trials were established, firstly, to quantify the gains that have been made in the first generation of improvement in the breeding programme; and secondly, to establish whether a number of seed source and orchard variables influence the performance of the progeny. These variables were: the number of flowering trees in the seed orchard, year of seed collection, seed orchard origin and composition of seed orchard seed bulks. Diameter at breast height and tree height were measured in the trials at between 87 and 97 months after establishment, and timber volumes and survival were calculated. Improved seed orchard bulks performed significantly better (p < 0.01) than unimproved controls in the field trials, and genetic gains ranging from 23.2 to 164.8 m3ha-1 were observed over the unimproved commercial seed. There were significant differences (p < 0.01) in progeny growth between the levels of flowering, with higher levels of flowering (R 40 %) producing substantially greater progeny growth than lower flowering levels (S 20 %). The seed orchard origin had no effect on progeny growth in this trial series. This suggests that seed collected from any of the four seed orchards tested will produce trees with significant improvement in growth. Various scenarios investigating a range of assumptions were developed and used to predict genetic gain in the F2 populations. These were compared with realised gains achieved in the genetic gain trials. The family nested within provenance scenarios proved to be closer to realised gain than the family across provenance predictions. Two scenarios were used for family nested within provenance: Firstly, actual flowering for family nested within provenance; and secondly, estimated flowering after a 30% roguing of poor families. For both scenarios, a coefficient of relationship of 0.33 predicted gains closest to the realised gains. Indications were that the effects were additive, and that very little or no heterosis had occurred. The statistical information suggested that outcrossing in the seed orchards was > 80%. This study provides an objective and quantitative assessment of the underlying assumptions used for estimating genetic parameters, and predicting gain in this population of Eucalyptus nitens. At the same time that genetic gain trials were established, F2 trials were planted, using seedlots collected from F1 seed orchards. Analysis of the two F2 trials showed that realised gains for diameter at breast height at 87 months were close to the predicted values and ranged from 1.02 cm to 1.90 cm. Two exceptions were the sites at Helvetia and Babanango, where gains were under- and over-predicted, respectively. Realised heritability estimates, which are related directly to the realised gain and the actual selection intensities used in the seed orchards, reflected this trend. Estimation of breeding values allowed for selection of elite individuals in top families. Both grand-maternal provenance origin and F1 maternal effects were significant in the F2 trials. A Type B genetic correlation of 0.61 for diameter at 87 months indicated the possible presence of genotype by environment interactions for the two F2 sites. A low narrow sense heritability estimate of 0.06 for diameter at breast height at 87 months at one F2 site indicated that more emphasis should be placed on family information rather than individual information at this site. A heritability estimate of 0.17 for diameter at breast height at 87 months at the second site, however, indicated that further improvement is possible in this population of Eucalyptus nitens. Modelling of predicted genetic gain using various breeding strategy scenarios can be a useful tool in assisting with the decision on which strategy or management plan will deliver the most genetic gains per unit time. Such modelling, using the parameters established in the first part of the study, played an important role in developing the advanced generation breeding strategy for Eucalyptus nitens. In addition, the modelling exercise highlighted various management options which could be used to increase gains in the existing production populations or orchards. Indications are that additional roguing of 1) existing Clonal Seed Orchards based on results of F2 trials (i.e., backward selection); and 2) F1 Breeding Seed Orchards based on stricter provenance selection, will markedly increase the quality of the seed produced from these orchards within one season. This study also highlighted the importance of shortening the breeding cycle in Eucalyptus nitens, particularly in view of the delays caused by reticent flowering and seed production in the species. The information and understanding gathered from this study led to the development of a proposal for an advanced generation breeding strategy in Eucalyptus nitens. This proposal uses parental reconstruction of open-pollinated progeny to secure pedigree information of forward selections, thus combining the benefits of increased genetic gain with a shortened breeding cycle. Recommendations on the management and adaption of current production populations to increase gains have been made, because establishment and management of improved material in seed orchards to ensure a sustainable supply of improved seed to the South African forestry industry, is a key objective of the ICFR Eucalyptus nitens breeding programme. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Clones of the Eucalyptus grandis x Eucayptus nitens (GN) hybrids were produced and selected through the CSIR‟s breeding programmes for colder plantation sites in South Africa. Some GN clones consistently exhibit high and superior pulp properties, which makes them valuable for commercial plantations in South Africa. In nurseries, stockplants are usually seven cm in length and maintained at high (100 x1.5 m-2) planting density. However, rooting frequency varies with season and little is known about the impact of position of cuttings on overall rooting frequency of a clone. The aim of this study was to investigate the effect of size and planting density of stockplants in mini-hedges, on the yield and subsequent rooting of cuttings from various positions of GN clones of known rooting potential (i.e. GN 018B: difficult-to-root and PP 2107: easy-to-root clones). Stockplants (10 cm vs. 20 cm) were established at high (100 x 1.5 m-2) and at low (25 x 1.5 m-2) densities for GN 018B and PP 2107 under commercial nursery conditions in a polyethylene tunnel. Cuttings were harvested every two to three weeks in September-October 2010 (spring), December 2010-January 2011 (summer), April-May 2011 (autumn) and June-July 2011 (winter). The harvested material was 5 – 7 cm in length and the light intensity received by individual stockplants at the two planting density levels was recorded. Harvested cuttings from the three positions (apical, middle and basal shoots) were used for: (i) rooting experiments under nursery conditions, (ii) bio-stimulant analysis using the mung bean bioassay, and (iii) analysis of soluble sugars. Between spring and summer 2010, the two GN clones established at low density yielded a similar number of cuttings, but differences in the rooting frequencies were significant in favour of PP 2107 clone. Similar observations were made at high density in terms of production of cuttings, but the significant differences in the rooting observations were reversed between the clones. The GN 018B clone had low rooting rates in summer under nursery conditions but its tissue extracts promoted higher rooting in the bioassay during that time, when compared to spring. Spring and summer had similar effects on rooting responses of PP 2107 cuttings in nursery and bioassay experiments. For both clones, short stockplants produced fewer cuttings but had a higher rooting frequency than cuttings from tall stockplants, with a high rooting frequency recorded from basal cuttings. Similar results were observed in the bioassay experiments which showed high rooting potential of mung bean hypocotyls cuttings using tissue extracts of PP 2107 cuttings maintained at high planting density. Although apical cutting tissues had high concentration of sugars (i.e. sucrose, glucose and fructose), their rooting rates were usually lower at high and low planting density compared to middle and basal cuttings. Sucrose concentration was the highest sugar present in stockplants grown under low planting density. A higher and lower rooting frequency was also observed in autumn although the two clones responded differently to Quambalaria eucalypti (Sporothrix eucalypti) disease infestations. Position, size and genotype had a significant impact on type and concentration of sugar (i.e. sucrose, glucose and fructose), particularly in PP 2107 clone, although rooting rates in the bioassay did not correlate with sugar contents of Eucalyptus cuttings. High carbohydrate (i.e. soluble sugar) content and auxin concentration increased production and subsequent rooting of cuttings across both clones, particularly in spring. Furthermore, rooting was enhanced by relatively higher light intensity intercepted by individual stockplants and in particular the GN 018B clone. Light intensity in the high and low planting densities caused variation in the rooting frequencies thereby increasing or decreasing soluble sugar and auxin concentrations of the two clones. Light intensity and fertiliser concentration received by tall and short stockplants impacted on endogenous hormone levels thereby increasing or decreasing rooting. High sugar concentration levels of PP 2107 clone increased its susceptibility to fungal infection thereby decreasing its rooting frequency in autumn, as its rooting rates increased in winter. Overall results of the investigation revealed that PP 2107 clone has higher rooting potential than GN 018B clone, in particular at high planting density and if stockplants are not infected by fungal diseases. Higher sugar levels were recorded in spring for PP 2107, although rooting rates of mung bean hypocotyl cuttings were higher in summer for GN 018B, suggesting that sugars have nothing to do with rooting of GN cuttings. Season, planting density and size of stockplants affect the rooting frequency of GN clone. Thus, short stockplants maintained at low and high planting densities are recommended for GN 018B and PP 2107 respectively, although the impacts of fertilisers and pathogen resistance on rooting rates still need to be investigated under similar conditions. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.