Tree help

Assisted conception of coniferous trees can be a boon for both the environment and the lumber industry

 
Last Updated: Saturday 04 July 2015 | 02:50:09 AM

FIRST, it was the test tube baby. Now, Canadian scientists are trying to do the same thing with coniferous trees. Assisted conception of conifers, they say, is all set to become the next big thing in forestry. By overcoming barriers between species, their technique could allow plant breeders to produce new hybrid conifer varieties.

Some species of conifer can interbreed, while others cannot, even though they have similar chromosomes and could theoretically produce viable off-spring. The main barrier is a structure called the nucellus, a layer of tissue through which pollen must extend a long tube to reach the female gametophyte. Pollen of the right species grows through the nucellus, but alien pollen is usually rejected.

Danny Fernando, John Owens and Patrick von Aderkas all plant embryologists at the University of Victoria in British Columbia, have now learnt how to get round this species barrier. They removed the nucellus from Douglus fir gametophytes which they then placed in a dish with pollen from the same species. After much trial and error, they found the right conditions to get pollen grains to germinate and extend their tubes into the gametophytes, reaching the ova inside. A five per cent solution of sucrose at pH 5.8 worked best, the researchers reported (Theoretical and Applied Genetics, Vol 96, p 1057).

A week after fertilisation, the researchers dissected the tiny plant and found they were developing normally. None of the plants has yet been grown into a young tree, but von Aderkas is confident that this should not be difficult. Similar embryos are routinely dissected from cones grown by botanists in laboratories, he says.

Fernando is now using the same method to cross two pines that do not normally hybridise, the western white pine and the bristleconc. Although the white pine gives much better lumber, it is easily affected by fungal infections called blister rust. By careful breeding and selection of offspring with desirable qualities, Fernando hopes to produce a hybrid combining the white pine's good wood and the bristlecone's natural resistance to the fungus. "We're very optimistic," he says.

The lumber industry is also equally optimistic. "I dare say that this technique would make hybrid development a lot easier," says Barry Herman, a forestry scientist with the timber giant Weyerhauser in Seattle, USA. He says that traditional breeding, which merely involves planting mixed stands of trees from two different species, is extremely inefficient, yielding perhaps just one hybrid per year from a stand of 10,000 trees.

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