Breeding trials and clonal propagation of selected species: 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.

NZDFI’s selected species on which to focus genetic improvement are:

  • E argophloia              Western white gum
  • E bosistoana              Coast grey box
  • E globoidea                White stringybark
  • E quadrangulata         White-topped box gum
  • E tricarpa                     Red iron bark

Trial sites – location and establishment

Between 2009 and 2012 NZDFI established base breeding populations of these species across ten sites. In 2016, a further three breeding trials were established. Over 70,000 trees have been planted to ensure that broad-based selection of elite trees is possible. The key species are:

  • E. bosistoana             192 families, 32,100 seedlings
  • E. globoidea               161 families, 26,640 seedlings
  • E. quadrangulata      104 families, 15,576 seedlings

We also plan 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 NZ’s eastern drylands. This range of sites will allow analysis of the stability of superior genotypes under contrasting environmental conditions by identifying the relative contributions of genetic and environmental effects.

Breeding population design

Each site 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

Before thinning - 6-year old E quadrangulata breeding trial at the Atkinson trial site

Thinned E quadrangulata breeding trial, Alexander trial site

Thinned E quadrangulata breeding trial, Alexander trial site

Early assessment of individual traits

In 2014 the first of a series of assessments, thinning and wood sampling operations commenced in the fastest growing sites, and these continued in 2015/16. Data analysis following these assessments is guiding the selection of plus trees at these sites.  Plus tree selections are being grafted by Proseed NZ for deployment in seed orchards while they also research vegetative propagation of NZDFI species in their new propagation facility at Amberley.  The assessment of wood quality traits in young trees has also started with a focus on early heartwood and growth stresses.

This early work will underpin our understanding of the genetic architecture (degree of genetic control and association between traits) for each species so that estimates of genetic superiority can be made for our genetically improved trees.

2015 and 2016 trial establishment, Murray's Nursery, Woodville

A further series of trials of E.bosistoana and E. quadrangulata families were planted in 2015 and 2016 under a Sustainable Farming Fund project. The primary objectives of these trials were to:

  1. screen at a young age for growth strain
  2. determine the heritability of this trait
  3. 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. 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.

More information on the Growth Strain project

The move to clonal propagation

Testing and deployment of genotypes can be undertaken with seedlings, clones or a combination of both. Producing planting stock by vegetative propagation (clones) of outstanding individual genotypes identified in progeny tests maximises the selection gains. In our first attempt at producing E.bosistoana cuttings for clonal plantings, the coppice from young seedlings was used.

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.

E.bosistoana is reported to coppice readily and we have observed this after thinning operations in the progeny trials. To test the potential to harvest coppice from older trees for clonal propagation, 33 trees were felled in the breeding population trial at Cravens Rd in October 2019. These trees were 10 years old and have a stump diameter average of 200 mm. The area around each stump was sprayed to maintain it clear of weeds to promote coppice regrowth.  Cuttings have now been set from this material by Proseed (in 2020) to progress the production of clonal tree stocks.

Read more about propagation work at Proseed

 

Coppice shoots on an E. bosistoana stump.