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Evaluation of the Ernslaw One Douglas-fir progeny tests

By Jaroslav Klápšte, Mari Suontama, Toby Stovold, Heidi Dungey , May 2018.

Download SWP-T049 (pdf)

Executive summary

This project evaluates a Douglas-fir open-pollinated progeny trial established on two New Zealand sites (Gowan Hill and Tramway), using seedlots from three Oregon (US) seed zones. The material was measured for diameter at breast height (DBH) and scored for forking (FRK), branching pattern (BR), straightness (STR), malformation (MAL) and acceptance (AC). A low level of plant survival was identified at the Gowan Hill site which prevented us from obtaining statistically significant estimates of genetic parameters. Results from this site should be considered with caution. Descriptive summary statistics found slightly better performance for straightness and forking in the interior seed zone compared with both coastal zones at the Tramway site.

Analysis of data from the Tramway site resulted in statistically significant estimates of heritability, indicating the possibility for genetic improvement in the assessed traits. Therefore, genetic improvement through breeding and selection can be achieved. However, it should be noted that open-pollinated experiments can suffer from over-estimated genetic parameters due to unrecognized relatedness from the paternal parent, and it is expected that the real genetic parameters may be lower.

Correlation analysis discovered two clusters of traits:

  • Acceptability (AC), malformation (MAL) and straightness (STR) – indicating a strong focus on stem form rather than productivity in acceptance evaluation; it also uncovered a strong negative correlation of this cluster of traits with forking (FRK), which is a favourable situation that supports the opportunity for simultaneous improvement across all the traits.
  • DBH, FRK and BR were moderately and negatively correlated with MAL – indicating the negative impact of fast growth on stem defects such as forks and ramicorns. Therefore, the selection of fast growing individuals will result in an increased incidence of stem defects and the trade-off between productivity and stem form should be considered.

The unexpected positive correlations between DBH and BR found in our analysis can be explained by the unreliable scoring of the BR at an early age, and we would recommend re-evaluating this trait in a later age when the crown is better developed.

Potential response to selection was generally higher in Tramway due to the higher heritability at this site. The highest improvement in DBH and FRK is achieved in Counties coastal zone. However, the unfavourable relationship between these traits prevents the simultaneous improvement in both traits. The highest response to selection in STR and BR is achievable in the Coastal interior zone and MAL in the Coastal zone.

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