Københavns Universitet
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PhD thesis defense

Jing Xu, IGN, defends her thesis about Christmas tree traits

PhD thesis defense — Jing Xu defence on 9 May at IGN


Date & Time:

Auditorium Von Langen, Department of Geosciences and Natural Resource Management, Rolighedsvej 23, 1958 Frederiksberg C

Hosted by:
Section for Forest, Nature and Biomass


Jing Xu defends her thesis,

Genetics of susceptibility to Neonectria neomacrospora and Christmas tree traits in Abies sp.

Senior Researcher Ulrik Braüner Nielsen, IGN
Associate Professor Ole Kim Hansen, IGN
Senior Adviser Iben Margrete Thomsen, IGN

Assessment Committee:
Professor Harry Wu, SLU, Umeå – Sweden
Professor Fikret Isik, North Carolina State University, USA
Senior Researcher Jon Kehlet Hansen (chair), IGN

Since the start of breeding Nordmann fir Christmas trees in Denmark in 1992, new challenges have arisen in the field of Christmas tree production. One of the most important is the challenge posed by the fungal pathogen Neonectria neomacrospora, which causes canker disease in true firs (genus Abies). This pathogen developed into an epidemic in 2011, affecting many Christmas tree stands in Denmark. Management of this canker disease is essential to ensure profitable Christmas tree production. In addition, the silver fir woolly adelgid, Dreyfusia nordmannianae, traditionally the most important pest in Nordmann fir Christmas trees in Central and Northern Europe, makes it very hard to avoid the use of pesticides. A way to deal with this adelgid is to attain more resistant plant material. Abies bornmülleriana seems less susceptible to this adelgid, making it a promising alternative species for Christmas tree production in Europe. Knowledge about genetic variation that can be used to develop breeding strategies (based on the testing of clones or progeny) for selecting more resistant individuals for deployment in the next breeding cycle is highly demanded. The present thesis includes five papers aimed at providing such knowledge based on a combination of quantitative genetics and tree resistance breeding studies.
Our studies have shown that N. neomacrospora is an aggressive pathogen in Abies species, and requires attention for the cultivation and conservation of the Abies species. Luckily, pronounced genetic variation in the susceptibility to N. neomacrospora has been observed in species, clones and family levels. The presence of a significant G×E interaction for susceptibility to N. neomacrospora in Nordmann fir suggests the need to implement breeding and deployment programs to select superior clones for specific environments. Both the natural damage evaluation and the experimental infestation test showed an interplay between the insect and the fungus on the Nordmann fir. It suggests that an effective pest management against D. nordmannianae might also reduce the risk of N. neomacrospora infections, and future studies on this topic could have important implications for suitable breeding programs for Nordmann fir Christmas trees and forest pest management. Combining modern quantitative genetic breeding methods and parentage analysis via DNA-markers (QFTs) to improve the genetic material available for Christmas tree production proved efficient in A. bornmülleriana. Backward selection is preferred due to the benefit of having a shorter time horizon for the delivery of improved genetic material, and using postharvest needle retention evaluations to potentially modify the selection is highly recommended. Here we propose to combine the results based on QFTs with selective seed harvest and paternity tests to give the best possible starting point forthe production of clonal A. bornmülleriana plants using somatic embryogenesis. Tests of N. neomacrospora susceptibility are desirable to confirm the suitability of using A. bornmülleriana as an alternative species for Christmas tree production in Europe.

The thesis is available for inspection from the PhD administration office 04.1.413 at Øster Voldgade 10