Overview
Most aspens don't propagate from dormant stem cuttings like other poplars but can be propagated via their roots. This paper describes techniques to propagate and ramp-up aspens from small diameter juvenile roots.
Research Papers Regarding Rootling propagation
The Effect of Root Segment Origin, Size, and Orientation in Aspen Rootling Propagation
Ten years of aspen tree improvement in Alberta-JeanBrourad (PDF)
Jean Brouard's Summary of Rootling Propagation Process
The following is a brief email summary of the aspen rootling process from Jean Brouard to Brad Bender on 7/5/2012:
The rootling method works like this:
1. Obtain some juvenile root tissues.
2. Use a piece of root 5-cm long and 2 to 5 mm in diameter.
3. Place it in your container vertically with the proximal side (to main axis of the mother plant) upwards.
4. If you water it and keep it warm, new shoots will develop from the root segment. New roots will develop from the root surface. At the end of one growing season you should have a plug with one stem and a well established root mass.
5. This method works for all aspen species I have tested: P. tremuloides, P. tremula, P. davidiana (actually P. tremula var davidiana) and also for hybrids including those of P. tremuloides with P. alba and P. grandidentata. It also works with hybrid poplar (Walker poplar) and balsam poplar (P. balsamifera). It should work more generally for any suckering species e.g. cherry, willow, elm?
1. Obtain some juvenile root tissues.
Juvenility of root tissues is important – anyone can produce suckers on roots of any age. Shoots from roots is easy! However, mature roots lose their ability to generate adventitious roots. Thus suckers from a mature root will have to be coaxed into producing new roots: this is done by severing the juvenile suckers, treating with fungicide, rooting hormone and kept in a well lit and well ventilated condition with frequent misting until new roots are formed. This is the traditional steckling method for aspen. It is a steckling method because stem cuttings are used (even though they are juvenile sucker stems). The disadvantage of this method is that it is fiddly, the suckers are fragile and it requires considerable care, attention and time. In practical terms one can collect 1-2 m long roots 2-5 cm in diameter. Place them in trays of vermiculite and harvest the suckers as they are produced. We developed the rootling method because we wanted to screen hundreds of clones and we needed sufficient ramets of each clone for balanced and fair comparisons. The first clones to go through the process produced much more robust stecklings than the last ones in a season so that we ended up confounding timing of propagation with genetic differences. It also occasionally occurred that we collected roots from more than one parent plant in the wild. Thus we sometimes started with a mixture of genotypes – also undesirable when doing genetic tests.
However, the steckling method does work. We still use it to grow mother plants that will be grown in containers as a source of root tissue for subsequent rootling propagation.
Collection of juvenile root tissue for direct rootling propagation is difficult. It does work but it is more fiddly. There is also the problem of staggered collection times which can confound genetic differences.
In summary: SHOOTS from ROOTS is EASY
ROOTS from SHOOTS is DIFFICULT
So use JUVENILE ROOTS which retain the capacity to generate new ROOTS
The steckling method relies on the fact that juvenile roots regenerate both
shoots and roots.
The best source of juvenile roots is a donor plant or mother plant grown in a container. We have used 1 gallon and 2 gallon pots. This works, but you get a limited volume of roots and they are all coiled up and tangled. We have used larger containers (e.g. trays) and these produce more roots. The very best method is to use hydroponics or aeroponics. This generates plenty of clean tangle-free roots that can be harvested at leisure and at the appropriate stage of physiological development (and size). Hydroponics works (I have used it) and it has the great advantage that the roots are readily visible and can be observed at any time for length and size since nothing needs to be dug up and disturbed.
2. Use a piece of root 5-cm long and 2 to 5 mm in diameter.
Size is important!
If it is too small you will get low success. If it is too big you will get low or no success.
The essential issue is the ability to generate adventitious roots – only young roots have this ability. Old woody roots lose the ability to generate new fine roots. It is possible that the issue is one of balance. Since any root maintains the ability to sucker it is easy to get new shoots that make excessive demands on the parental roots with respect to water and nutrients. So if the root segment is too large (e.g. over 1 cm in diameter, the developing suckers will suck the root dry and there will be no resources available for developing roots.
Essentially the beauty of using juvenile root segments is that both root and shoot initiation start at the same time and there are no excessive demands from the developing shoots.
Maybe, the juvenile root segments are successful because they still have the capacity absorb water and nutrients where large woody roots have an anchoring function and a reproductive function (through suckers after disturbance from fire or wind).
Open4st Aspen Rootling Propagation
Overview
Below is a summary of the Open4st indoor aspen rootling process. It is intended as a general guideline that will be updated over time.
Materials: