Monitoring and managing genetic diversity in Sitka spruce

Summary Description:

This study will quantify baseline levels and changes in genetic diversity during the course of the UK's Sitka spruce genetic improvement programme.  Using microsatellite markers, the study will first determine the quantitative measures of genetic diversity in native QCI populations and unimproved commercial stands of Sitka spruce in the UK to estimate any reduction in genetic diversity that occured in the introduction process.

The project will then go on to measure how this introduced genetic diversityhas changed as a consequence of the different tree improvement strategies, either seed orchards or vegetative propogation, employed to produce stock.

The study will provide important information to help guide the future development of the Sitka spruce improvement programme.

Project Outcomes:

Lay Summary of Thesis:

This thesis presents the final results of the PhD project that conducted the first systematic genetic assessment of the British breeding programme for Sitka spruce (The programme). The main emphasis was on defining levels of neutral genetic diversity.

The importance of maintaining neutral genetic diversity has been widely included in modern breeding programmes. This is because neutral genetic diversity provides a higher adaptive potential of trees inside The programme for any potential environmental changes.

The project's main aim, was to compare assumptions based on the population genetic's theory and written records by different stakeholders of The programme with the results from genetic monitoring.

Presented genetic monitoring consisted of molecular and non-molecular methods of observing a plant's genotype and phenotype. While molecular markers provide more exact estimates of genetic diversity, the simpler non-molecular observations are a complementary tool for managers' everyday use in The programme. Together they allow for a better interpretation of the results.

1. British breeding programme was divided into three components:

2. Clonal archives - store reference genetic material used by The programme.

3. Clonal seed orchards - produce the highest percentage of forest reproductive material (FRM) sold on the British market.

Control-cross programme - produces highly improved FRM from two selected parents and is of lower genetic diversity.

These three components were examined by sampling them at different stages of The programme. Either at its a) reference stage by sampling individual plus trees; b) production stage by sampling seed production in the orchards, seedlings growing on the nursery beds, cuttings from clonal hedges and finally, at the c) plantation stage by sampling trees for wood production.

To assess the extent of genetic diversity reduction, all three components sampled at three stages were compared with the natural populations from USA and Canada and British unimproved populations. These served as a benchmark for genetic diversity.

The following main results of the PhD project are presented in no particular order of importance for understanding and improving The programme:

1. High levels of genetic diversity were measured at all stages of The programme (Chapter 1). At the seed orchard FRM production level, diversity is at its highest level, exceeding diversity stored at natural populations.

2. Genetic diversity reduction of seed orchard FRM is driven by the unequal contribution of parents planted inside the orchards (Chapter 2 & Chapter 3). Adverse events such as frost or drought reduce levels of genetic diversity since several parents contribute significantly more to the sampled seed crop. The lower production of seeds often exhibits genetic diversity loss. In such cases, mixing different seed years would improve the genetic diversity of FRM on the British market.

3. Genetic diversity levels observed at the highly improved FRM planted on forest plantations suggest several errors being made at The programme that contributed to lower genetic gain than expected. This result shows the importance of introducing molecular methods in FRM tracking.

4. Genetic diversity levels observed in control-cross operations in the tree nurseries suggest several contamination points. While certain levels of pollen contamination are somewhat expected, the levels presented in Chapter 4 could be further reduced.

5. Among molecular methods tested in this thesis, microsatellites performed consistently well and provided a good option for assessing genetic diversity, parentage analysis, and quality tracking. On the other hand, the SNP Sequenom assay used for the first time in this PhD project needs additional testing and optimization for consistent results.

6. Levels of contamination from beyond the orchards are low (Chapter 3). Results suggest a high probability of mother trees being pollinated by nearby trees. 240 m was the longest distance between a mother and a father tree measured in this project.

7. Transitioning from unimproved or seed orchard's FRM plantations to continuous cover stands keeps desired genetic diversity in natural regeneration.