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OFRI researchers working on tree improvement have made progress in solving a challenging problem when it comes to propagating jack pine seedlings that have desirable genetic traits: They’ve improved a method to root cuttings, which has been notoriously difficult to do with jack pine. And they’re the first researchers to test how well jack pine rooted cuttings perform in the field.
According to OFRI Research Geneticist Pengxin Lu, leader of the jack pine rooted cutting study, this advancement will help speed production of jack pine seedlings with desirable traits, such as improved growth and reduced branchiness, which in turn will help forest managers grow healthier, more productive, and more valuable future forests.
“In Ontario, tree improvement programs have traditionally focused on growing bigger trees more quickly.” Lu notes. “For jack pine, that focus is shifting to improving the quality of individual trees and minimizing growing costs. Our ability to improve jack pine tree form and branchiness and propagate elite seedlings using this method is going to be very useful for future forest renewal.”
So what’s a rooted cutting anyway?
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| Researchers led by OFRI Research Geneticist Pengxin Lu have improved a method to get jack pine to produce proliferated dwarf shoots, which grow out from base of needle clusters or fascicles (A). They then used these shoots to produce seedlings that are genetically identical to the donor trees (B). |
A rooted cutting is a part of a tree—often a branch tip—that is cut off and placed in soil to develop roots and become a new tree, one that is genetically identical to the donor tree. Rooting cuttings is one form of vegetative propagation or asexual reproduction.
According to Lu, being able to root cuttings is very useful to tree improvement. Trees grow slowly and can take years to decades to produce seed. And even when researchers are able to completely control pollination, they can’t be sure the seed will produce new trees with the same characteristics as the parent tree.
To speed tree improvement, researchers use shortcuts to produce genetic copies of trees with desirable traits. Rooting cuttings is one of these shortcuts, as it results in new trees in much less time than growing trees from seed.
“Large-scale vegetative propagation has so far been done via rooted cuttings and more recently, via somatic embryogenesis,” Lu explains. “Rooted cuttings help to fast track breeding programs and achieve greater genetic gains by focusing on quickly and efficiently propagating exceptional individuals with optimal genotypes.”
Why has rooting jack pine cuttings been so difficult?
In nature, many tree species can reproduce themselves via vegetative propagation. Aspen, for example, produce new trees by suckering—sending up shoots from their roots. But jack pine and several other conifer tree species reproduce only from seed, not via sprouting up from a root or other part of an existing tree. And jack pine’s ability to root falls rapidly with age, making it challenging to propagate vegetatively even in a research greenhouse.
Their key to success? Dwarf shoots!
According to Lu, other researchers have had promising results with vegatively propagating various pine species by cutting off the new, green shoots at the ends of branches and rooting them. However, this method does not work well for jack pine.
In the late 1990s, researchers discovered that using proliferated dwarf shoots—ones stimulated to grow out from the base of needle clusters or fascicles—increased rooting rates in jack pine. So Lu decided to give that a try.
To promote dwarf shoots, he removed the apical buds from the tips of donor seedlings. When shoots reached at least 4 centimetres long, he cut them off and planted them in growth medium. After several months in an OFRI greenhouse, up to 70 per cent of the cuttings rooted.
“We didn’t know how these rooted cuttings would perform,” Lu says, “because the only research done before us was on a small scale, and no trees were field tested. Our concerns were that even if we could get the proliferated dwarf shoots to root, the cuttings might grow slowly and turn into multi-stemmed trees with poor form. We were also unsure how well they would survive and grow when planted. So we decided to propagate at a large scale and establish field trials for long-term testing.”
According to Lu, the rooting portion of the study was very successful: “We achieved similar rooting rates as those reported in previous research elsewhere but without applying growth hormone treatment, which simplified the rooting procedure and reduced our costs.”
…and how did the trees from proliferated dwarf shoots perform in the field?
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| Eight years after planting, jack pine grown from proliferated dwarf shoots are thriving on the Sioux Lookout NEBIE site, performing as well as conventional seedlings. |
Lu and his research partners (OFRI Forest Ecology Research Scientist Wayne Bell, Paul Charrette of the Superior Wood Tree Improvement Association, and Megan Thompson of RW Forestry) compared survival and growth of trees grown from proliferated dwarf shoots with that of comparable conventional seedlings grown from seed from commercial stock. The trees were planted on two test sites: the NEBIE plot network site near Sioux Lookout and the OFRI arboretum near Sault Ste. Marie. Bell says, “After eight years in the field, trees from cuttings were keeping pace with conventional seedlings and had acceptable growth form.”
He adds that in the Sault Ste. Marie planting, the rooted cuttings were less branchy than the conventional seedlings, so they will likely produce higher quality wood when mature. “From a silvicultural perspective, this is huge,” he says. “It means we can plant fewer trees per hectare and not have to worry about poor form or excessive branching, greatly lowering plantation establishment costs.”
Lu notes one remaining concern is whether the rooted cuttings planted on sandy soil are as wind firm as conventional seedlings. He says, “We need to monitor the trees over the long term to determine whether tree stability will be an issue.”
For details, e-mail information.ofri@ontario.ca and ask for the journal article entitled Performance of Jack Pine Rooted Cuttings From Proliferated Dwarf Shoots Versus Seedlings Eight Years After Cutting from Canadian Journal of Forest Research.
Did you know...? facts about jack pine
Many Ontarians are very familiar with red and white pine, which are both very common in southern Ontario.White pine especially gets lot of attention, as it is Ontario’s provincial tree and the king of eastern Canada’s forests, soaring to massive heights and living 500 years or more.
But what about jack pine? While it does not live as long or grow as massive as its red and white cousins, the jack pine is scrappy, tough, adaptable, and very useful to people. The oldest known jack pine in Ontario (near Blue Lake near Timmins) is 250+ years old.
Did you know that jack pine…
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| Jack pine cones resemble rams’ horns and are glued shut with resin. They need the intense heat of fire or hot sun to open and release seed. |
- Is the most widely distributed pine species in Canada?
- Is the second most important commercial tree species in Ontario (based on volume harvested)? The most important is black spruce.
- Can grow almost anywhere, including on sand, permafrost, and shallow soils over bedrock? However, jack pine does not like shade or very wet areas. It grows much better in the open than under a canopy of larger trees. OFRI research has shown that jack pine does not grow well with large-leaved aster in clay soil because the aster showers the seedlings with a deadly needle rust fungus.
- Has needles that grow in groups of two, and cones that grow in pairs like rams’ horns (see photo)? When trying to identify an Ontario pine tree, remember:
- White pine needles grow in groups of five.
- Red and jack pine needles grow in groups of two, but jack pine needles are shorter, spread out in a V shape, and tend to be slightly twisted. Red pine needles are longer and straight.
- White pine cones are large and long, red pine are short and wide, and jack pine’s are the smallest (again, think rams’ horns!).
- Rise first from the ashes of forest fires? The jack pine is a pioneer tree species, which means it’s usually the first in the boreal forest to grow back after a fire (see photo). Their cones are serotinous, which means they are glued shut with resin and burst open to release seed in response to an environmental trigger (fire or a hot sunny day). Jack pine have the smallest winged tree seeds of any native North American pine.
- Is very important to the endangered Kirtland’s warbler, one of the rarest members of the wood warbler family? This bird, which is rarely seen in Ontario, nests only in 5- to 20-year-old jack pine stands. Many other birds and mammals make jack pine stands their homes and feed on jack pine seeds and foliage.
- Is used mostly to make paper but also for lumber, medium-density fibreboard, telephone poles, railway ties, mine timbers, fence posts, and firewood? First Nations people used jack pine to frame their canoes.
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| Jack pine is a pioneer species, which means it's the first to rise from the ashes after fire. |
