Scientists at Teagasc's Kinsealy Research Centre have turned back the clock for old trees, reversing the ageing process and making old plants act like saplings, writes Dick Ahlstrom.
An Irish research team has "reset" the biological clocks of old trees. Plant material taken from near century-old ash trees has been made to root and grow as well as any seedling.
The discovery could have implications for the forestry industry, which needs high quality trees for processing. The goal is to find the best trees and then propagate fresh plant material from them to grow new forests.
"The ash is a very important tree for Ireland," explains Dr Gerry Douglas, senior research officer at Teagasc's Kinsealy Research Centre. "We are planting about 1.5 million ash trees a year," he says. "These are fresh forests, but we have noticed that the quality of these forests could be improved."
There is widespread interest in this important tree species right across Europe, he says. Douglas coordinates an EU project aimed at improving the ash tree, a four year, €1.2 million effort involving 15 partners in six countries.
"It is all dedicated to ash trees," he says. "Ash is a very important tree for Europe. They run from the Atlantic in the west to Russia in the east, and from Scandinavia to the Mediterranean."
The research into improving the ash tree involves several approaches, he says. One is a "European provenance trial" involving all six partners and tree seeds collected from 60 different regions across Europe. Each country will plant a "core" sample of 30 seed types and one member, France, will try to plant all 60 varieties. The object is to find the small collection of ash varieties that give the best results across the widest range of localised climates.
While this will identify those varieties with the widest growing range, this won't help improve the quality of ash already standing in deciduous plantations. For this advanced propagation techniques had to be applied.
In theory, propagation should be a simple process. First you find a superior tree with the best shape and timber yield, take cuttings to propagate fresh plant material from it and then grow an entire forest sired by this one superior tree. Unfortunately this doesn't work, explains Douglas.
"We would like to take cuttings from them, but they don't root when they are from old trees." The cuttings survive in compost but do not root and so are never viable. By comparison, cuttings taken from immature saplings root nearly 100 per cent of the time.
Mature trees lose the characteristics of youth as they mature. Just as a juvenile can't produce seed, a mature tree can't behave like a sapling, explains Douglas. "They can do things in the juvenile stage they can't do in the mature stage. Rooting is a juvenile trait."
Another is the ability to grow straight. Some mature tree cuttings from branch tips will grow at an angle from the perpendicular as if still a branch rather than a fresh cutting. "We want to recover the juvenile characteristics both in rooting but also in growth pattern," says Douglas. It now looks as if the Kinsealy team have achieved this goal, turning back the biological clock of the ash.
He could have tried very specialised micropropagation, the treatment of cells taken from the ash trees and then cultured to produce plantlets. This is both expensive and laboratory-based, however, and too elaborate for mass production of viable plant material.
Instead, Douglas put together a more round-about method that took more steps but is now producing rooting ash saplings, viable clones derived from a mature tree. His group actually looked at plant material from 60 superior trees but in just 15 cases could the material be coaxed into growth.
The process starts with "crown cuttings" from the tops of mature trees. These are grafted to sapling root stock and buds are then taken from these grafted plants when they begin to grow. The buds in turn are sterilised to suppress disease and then treated with nutrients and growth regulators to stimulate the production of shoots.
These shoots, in turn, are taken as cuttings and then rooted in the normal way. Once roots form they are brought on as plantlets in the greenhouse until ready for planting outside. As with ordinary cuttings, they can be bulked up quickly. A single ash tree bud grafted and then brought on in this way can be used to produce hundreds of thousands of plantlets within six months, says Douglas.
So far, Douglas and the team at Kinsealy have collected viable cuttings from five mature superior trees, with cutting success ranging from 70 per cent up to 100 per cent. "We feel fairly confidently that we have taken two characteristics back to juvenility," he says. The plantlets have rooted well and are also growing straight and true, with no drift off the perpendicular, he says.
The research group are well aware of the risks associated with monoculture if cloned versions of a single tree are used in all future ash plantations. This could lead to a loss of diversity, something he is not going to accept. "We do not want to narrow the genetic base of the ash tree," he says.
With this in mind, the Irish team is working with 90 trees from all over the island of Ireland and genetic studies are underway to assess diversity on the level of genes. The French participants have also carried out a "paternity" analysis in a 20 acre stand of ash to understand relatedness between individual trees.
Every tree in the 20 acres was fingerprinted and seed was collected from 25 individuals. The researchers found that 83 per cent of the pollen that ripened the seed came from outside rather than inside the 20-acre stand. Seed setting seemed to favour pollen arriving from beyond the closest trees.
Increasing the proportion of superior trees in a given stand has a major impact on the value of the stand. A poor quality tree is usually only good for firewood and is only worth about €20 per tree. A superior tree will deliver one to 1.2 cubic metres of timber which, if veneered, would fetch €500, says Douglas.