3 December 2018

Research to stop Christmas trees from losing needles


Nordmann Fir is the Christmas tree of choice among Danes. However, the variety has been losing needles from the innermost part of its branches, a problem that costs tree growers between 20 and 50 million kroner in lost annual revenue. Now, researchers at the University of Copenhagen are looking into whether bad genes might be to blame for this widespread damage.

The Danes' favourite Christmas tree, Nordmann Fir, suffers from "bare shoulders" – a phenomenon that has been common in Danish Christmas tree plantations since 2014.
The Danes' favourite Christmas tree, Nordmann Fir, suffers from "bare shoulders" – a phenomenon that has been common in Danish Christmas tree plantations since 2014.

No one would pay full price for a half bald Christmas tree. The deficiency disease that causes Nordmann Firs to shed needles on the innermost part of branches is known as "bare shoulders". The industry estimates that between 20 and 50 million kroner are lost annually due to price reductions or the inability to sell the affected trees.

In recent years, the industry has attributed this tree balding or discoloration to a lack of magnesium, a problem they thought they could fertilize themselves out of. However, the code to this plant disease has yet to be cracked. Researchers from the University of Copenhagen’s Department of Geosciences and Natural Resource Management now point out that magnesium deficiency is not the entire explanation, and that some Christmas trees are just more genetically predisposed to acquiring "bare shoulders" than others.

"We see that while some trees in stands of Christmas trees get ‘bare shoulders’, neighbouring trees in the same row do not, despite sharing the same soil and fertilizer. Therefore, we believe that trees with certain genotypes are more predisposed to being affected. For example, it is thought that trees have differing abilities to capture or make use of magnesium," explains Associate Professor Ole Kim Hansen of the Department of Geosciences and Natural Resource Management.

Removing bad parents

Researchers now want to examine the role of genetics so as to be able to weed out trees that are genetically predisposed to bare shoulders. This would allow for an improvement of Danish seed stocks and ensure that the Christmas tree industry has access to better genetic material.

"To identify problem trees, we have started measuring data from other ongoing Christmas tree trials out in the field. It is still at a preliminary stage, but we hope to have the opportunity to expand our research so that we can minimize the risk of damage,"says Ole Kim Hansen.

The researchers also want to use DNA markers on trees in commercial Christmas tree plantations. DNA-markers can identify parent trees to trees with bare shoulders. These "bad parents" can then be removed from the seed stocks that were originally supplied to the plantation.

Interaction between heritage and environment

When we humans get sick, it is often due to an interaction between genetics and environment. The same goes for plants. As a result, researchers will combine their genetic studies with work to analyze soil nutrients and needles from individual cultivation sites. By doing so, they will be able to examine the level of magnesium, which likely plays a major role in determining which trees end up with bare shoulders. The work builds on previous research, in which fertilisation alone was the focus.