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C/- Marlborough Research Centre Trust, PO Box 875, Blenheim 7201
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BREEDING TRIALS: ACHIEVING GENETIC GAIN
Base breeding populations of our selected species have been established on 13 contrasting trial sites across NZ’s eastern drylands regions. These trials are the foundation of our tree improvement programme.
Large breeding populations ensure that a broad range of genetic diversity is captured from which to select multiple traits for improvement.
Breeding trials: species selection
The focus of NZDFI's genetic improvement work has been on two species:
- E. bosistoana Coast grey box
- E. globoidea White stringybark
Other species included in our breeding work:
- E. quadrangulata White topped box
- E. argophloia* Western white gum
- E. tricarpa Red iron bark
* E. argophloia was eliminated from the breeding programme in 2023 following a review of all species' performance across our trial network.
Trial sites – location and establishment
Between 2009 and 2012 NZDFI established base breeding populations of these species across ten sites. In 2016 and again in 2021, a further three breeding trials were established. Over 90,000 trees have been planted to ensure that broad-based selection of elite trees is possible. The key species are:
- E. bosistoana 254 families, 44,052 seedlings
- E. globoidea 161 families, 26,640 seedlings
- E. quadrangulata 104 families, 15,576 seedlings
We also planned to research and develop inter-specific hybrids - hence the more limited plantings of E. argophloia and E. tricarpa.
The 13 different sites cover the range of abiotic (cold, drought, soils etc) and biotic (pests, diseases) stress factors likely to be found in New Zealand’s north-eastern drylands. This range of sites allows analysis of the stability of superior genotypes under contrasting environmental conditions by identifying the relative contributions of genetic and environmental effects.
Breeding trial locations.
In 2023, an evaluation of species performance in our trials led to the decision to drop E. argophloia from the breeding species list. We have yet to make progress with E. quadrangulata as so far it has not been seen flowering in any of the trials. In future we hope to add E. macrorhynca (red stringybark) into our genetic improvement programme.
Breeding population design
Each breeding trial is planted in separate blocks of each species. The individually labelled trees for each family are laid out in a randomised design. Trees are planted at 2315 stems per hectare (1.8m x 2.4m). Each species is replicated at three different sites.
This design ensures control of environmental variation at site level, and enables between- and within-family selection. Permanent sample plots (PSP’s) have been established for measuring productivity and developing growth models.
Before thinning - 6-year old E quadrangulata breeding trial at the Atkinson trial site
Thinned E quadrangulata breeding trial, Alexander trial site
Assessment of individual traits
In 2014 the first of a series of assessments, thinning and wood sampling operations commenced in the fastest growing sites. These have continued since then with many of the 2009, 2010 and 2011 breeding populations having had two growth and form assessments. In addition, wood quality traits assessments have focused on early heartwood, durability and reducing growth stresses.
Data analysis following these assessments has guided the selection of plus trees at these sites. Plus tree selections have been grafted by Proseed NZ for deployment in seed orchards at Amberley with the E. bosistoana and E. globoidea orchards starting seed production in 2020 and 2021 respectively.
Work investigating into the E. bosistoana and E. argophloia genome was undertaken at the School of Forestry. This work enables us to better assess the opportunity for selection of these species as it underpins our understanding of the genetic architecture (degree of genetic control and association between traits). Combined with our assessment data we will be able to determine the degree of genetic superiority captured in XyloGene nursery stock.
2015 and 2016 trials, Murray's Nursery, Woodville
A further series of trials of E.bosistoana and E. quadrangulata families were planted in 2015 and 2016 under a MPI-funded Sustainable Farming Fund project. The primary objectives of these trials were to:
- screen at a young age for growth strain
- determine the heritability of this trait
- initiate a clonal testing programme from coppice cuttings.
Seedlings were planted at an irrigated nursery site at Woodville in blocks of 8 trees, replicated between 2 and 8 times, depending on the number of available seedlings per family. The families were randomly allocated within the replication. At age 1-2 years old the trees were measured for growth then harvested and the stems assessed for growth strain using a splitting test developed by the University of Canterbury. Stiffness, twist, density, shrinkage, and acoustic velocity was also recorded. A selection index from the breeding values of these traits was used to identify the individuals in the Woodville trial for propagation.
The cut stumps were allowed to coppice and provided the material for cuttings to be raised by Proseed. A clonal test of E. bosistoana was planted in 2018 at two locations in Marlborough with cuttings propagated from this seedling coppice by Proseed NZ at their Amberley propagation facility. This was our first attempt at producing E.bosistoana cuttings for clonal plantings.
The time-frame between seedling progeny testing and clonal deployment could be shortened if selections in progeny trials could be felled and the coppice harvested for cutting production.
Coppice shoots on an E. bosistoana stump.