CHRISTMAS trees from Europe and Japan are rescuing their American brethren
from a fungal enemy. The soil fungus, Phytophthora cinnamomi, threatens
to decimate plantations of Fraser fir in North Carolina. These luxuriant trees
adorn 6 million homes in the US during the festive season, making North Carolina
the second largest supplier after Oregon.
The fungus, which attacks the trees鈥� roots, is posing an increasing threat,
and researchers at North Carolina State University in Raleigh are hoping to stop
it in its tracks.
鈥淚n a recent survey, 6 to 8 per cent of Fraser fir stands were affected, and
Phytophthora seems to be spreading,鈥� says Eric Hinesley, professor of
horticultural science. 鈥淥nce we have it in a field, there鈥檚 no way to get rid of
it,鈥� he says.
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To counter the threat, Hinesley and his colleagues John Frampton and Michael
Benson have enlisted foreign Christmas trees which seem more resistant to the
fungus. They鈥檙e also seeking strains of Fraser fir with natural resistance.
To find suitable relatives, Hinesley screened several in the lab, exposing
them to the fungus. Hardiest of all was the momi fir from Japan. Nordmann fir,
the most popular Christmas tree in Europe, was next most resistant, alongside
its cousin, the Turkish fir.
Next, Hinesley grafted the roots of these resistant varieties onto Fraser fir
trees. To do this, he grew saplings of each resistant variety to a height of
around 30 centimetres, then made vertical slits in each central shoot. Into each
slit, he grafted an 8-centimetre-long twig from the Fraser fir. 鈥淚t means we
have a Fraser fir, but on top of a root system of a different species resistant
to the fungus,鈥� says Hinesley. He planted the grafted trees earlier this
year.
To find Fraser firs that are naturally resistant to the fungus, Frampton
exposed hundreds of seedlings to it. Most died, but around 2 per cent survived,
suggesting they might have resistance that can be cross-bred into elite
trees.
Frampton also visited abandoned plantations and found a few trees which had
survived and might be resistant. 鈥淎ll the trees had gone except one or two,鈥�
says Hinesley. 鈥淛ohn has taken cuttings and rooted them, and is evaluating them
to see if they鈥檙e resistant.鈥�