The 2020 Open4st project investigated nursery, field, figured wood and r4st database strategies to prepare for future regional field trials with select hybrid aspen materials. The importance of establishing regional field trials is explained in the 2018 document, “Low-Resource Aspen Breeding and Nursery Selection Strategies”, which also provides a historical Open4st project perspective. These 2020 tests were statistically non-significant and are considered as pilot tests to investigate if further testing is warranted.
2020 Bell Nursery Summary
Context of the 2020 Nursery: Most of the 2020 Bell Nursery cutting material was planted on 5/02/2020 in a 1000 square foot composted, roto-tilled nursery (40' x 25'') with rows on 36" centers having dual rows of cuttings 4" apart and cuttings planted 5 to 6 inches apart in each row. The ramet cuttings were 8" long with diameters ranging from 6mm to ~14 mm. All material was cut from heeled in whips in mid March, banded with their planting label and stored in a refrigerator at 30 degrees F. until Spring planting. The internal 4" between the rows was covered with MiracleGro Sphagnum Peat Moss. The area between the double rows was treated with glyphosate to control mid-summer weeds. The nursery was irrigated with a 9' tall sprinkler. The nursery is slightly sloped from South to North allowing excellent drainage with the rows and a drainage ditch on the North side. Miracle Gro 20-20-20 soluble fertilizer was applied to the rows in late June and twice in July similar to past years.
Summary 2020 Nursery Results: A total of 1259 dormant cuttings and rooted mini-stools were planted in the 2020 nursery of which 403 survived that were of robust ministool grade (>3' tall). However the mean effective overall survival was 55% which included weaker trees 1-3' in height. Some of the 25xr P. x rouleauiana (AxG) materials have a chlorotic leaf condition, which has managed by selecting less chlorotic clones since the seedlings were produced in 2016. This is likely a genetic condition since it has been consistently observed on specific clones at consistent rates. The late season excess rain caused mildew on some of the large AxG leaves. See 2020-Bell-Nursery Photos and vw_2020_8_stock_summary).
Dormant Cutting Woods IBA Rooting Test: A dormant cutting propagation test was conducted in the 2020 Bell nursery using Woods Rooting Compound with 3 treatments and a control (Table 1). The test involved 317 8” dormant cuttings stored at 30 F. Cuttings, soaked 18 hours, air dried, dipped in the Woods solutions via 3 rates then immediately rinsed in water and planted in the nursery. The mean survival rate was 66%. While this test is not significant due to the small sample size, it is interesting to note the mean rooting rates had a 4.6 population standard deviation suggesting that the Woods Rooting compound did not significantly affect propagation rates for this test. A 2020 16 day indoor propagation test with 4” dormant cuttings and 3 Woods Compound rates showed interesting results with 3 of 6 treatments rooting at 100% and no rooting for the non-treatment control (see: 2020-Woods1 Rooting Test). A similar indoor test will be repeated on a larger scale for 2021 using 6” dormant cuttings, T5 lights and outplanting the surviving stock to the nursery and/or a field planting site. See: vw_2020_2_5_nursery_woods_summary.
Table 1. 2020 Bell Nursery Dormant Cutting Woods IBA Rooting Test
2020 Figured Wood Tests
There were 82 aspen clones tested for figured wood via the split wood test with 7 clones identified as having a mean undulation figured rate of 2 or higher (3 is highest). Ten figured aspen clones have been carried forward in the 2020 nursery.
Four 2020 Field Plantings
There were 307 aspen trees planted on 4 field test sites in 2020 with a mean one year survival rate of 97% and 65 cm mean height (Table 2). The material was a mix of 1-0, 14” dormant cuttings (DC) and 14” 1-0 root pruned cuttings referred to as “ministools” (See photo: 14” rooted ministools). Field trees were also protected with 18” and 36” white fabric, bamboo staked tree shelters (see Multi-Stage Aspen Planting Strategies).
Table 2. 2020 Open4st Field Trial Summary: 307 Trees, Four sites, Four Stock Types
Field Trial Master Summary Table Data: This r4tst online database table lists summary statistical data for all open4st plantings grouped by the clone names with the number of sites, years planted and number of stock types. It also includes the summary data, "avg_field_cuttings_ft" column for the mean 12" field cuttings per tree and the "sites_plustree_survival_score" metric which employs a weighted formula to gauge clonal performance across a variety of sites, plus tree scores and survival rates. The need for this data was driven to help understand the un-replicated nature of the trials at this early stage. Hopefully, future replicated regional field trial data will provide a clearer picture of the clone and site interactions.
Tentative 2021 Field Trial Strategy
The tentative 2021 field strategy is to plant about 300 trees consisting of the top 20 2020 nursery selections and previous elite clones on two local sites using 1.5’ protective tree sleeves. Twelve of these clones (see: vw_2020_future_field_trial_clones) will also be ramped up in the 2021 Bell nursery to produce about 50 trees per clone by 2022 (~600 total trees). The 14” ministool 1-0 materials could be available in the Spring of 2022 for future field trials depending on resources and the clonal trial design. These diverse aspen materials represent 12 different clones from 9 different families, hybrids and pure species.
The primary 2021 field field trial will consist of 256 trees representing 20 different hybrid aspen Poplar varieties from 9 different families (see: 2021-PostSE-FieldTrialTrees). The trees will be planted on the Post SE site number 4.1 with 8’ x 8’ centers in randomized 4 tree plots within 4 - 64 tree blocks (8 East/West rows by 32 North to South columns) to test 7 treatments and a control (Table 3). Each 4 tree plot will have 2 control and 2 treatment trees (see: 2021 Trial Map). This site is a challenging upland site with a southern exposure and a West to East downward fertility gradient. It may be a good site to test clone to site variation per treatment and select clones suitable for a drier climate over time. The expectation is to plant a future statistically relevant field trial to the South of the 4.1 site with fewer clones and treatments then later scale the best materials and cultural treatments for regional field trials.
Table 3. 2021 Open4st 256 Tree Field Trial Treatments.
Aspen Rootling Propagation
Most aspens don't propagate from dormant stem cuttings like other poplars but can be propagated via their roots. The following aspen rootling propagation process describes techniques to ramp-up aspens from small diameter juvenile roots. It is intended as a general guideline that will be updated over time.
Materials and Methods:
T5 Lights: 48" Sunblaster 904298 NanoTech T5 High Output Fixture Reflector Combo
Hang one 48” light over the length of 2 flats or 2 lights across the width of 4 flats with 6" to 10" from the plant tops.
Heating Pad: 48” x 20.75” seedling temperature adjustable heating pad
Media: Epsoma Organic seed starter media - mixed 2:1:1 with Epsoma, vermiculite and Perlite (aka EVP).
Fertilzer: Safer Brand Awaken Liquid nutrients - mixed with 1.5 tsp per gallon water (lasts 1 week).
Humidity Domes: 2” and 7” ventilated flat greenhouse dome covers - High humidity is needed for starting rootlings and maintaining the shoots in a less lignified state for easier propagation of the shoots.
24 hour timer: Adjust timer to 18 hours on and 6 hours off. Set light distance to 6" from the top of the flat tray.
Misc supplies: Razor, marker, blue tape (labeling), spray bottle, 1 or ½ gallon jug, (meat) thermometer.
Establish Primary Rootling Stools:
Collect dormant juvenile aspen roots before bud break in early Spring (March in Michigan). High quality root material can be obtained from 1-0 aspens grown in 2” x 5” deep cells or via large scale aspen root propagation.
Cut the roots to 50 mm long by 2-5 mm in diameter and band them so they can be planted with the proximal end up.
Label the 6 cell tray or entire flat with blue tape and a marker with the date, variety and applicable treatment code that will be tracked.
Add the EVP soil media to the trays and moisten it with the liquid fertilizer solution to allow easier planting.
Insert the root cuttings with the proximal end up and set the tray in the flat with about ½” of water to allow it to soak into the media until saturated.
Place the 2” dome over the flat place on a flat bench with 6 hours of darkness and adjust the heating pad to maintain about 60 F. night and 72 F. daytime temperatures. Keep the top dome vents ½ open and sides fully open.
Water by filling the ¼” grooves of the tray bottom with the fertilizer solution every 3 days. Adjust as needed to maintain moisture droplets on all sides and small portions of the top.
It may take about 30 days for the root cuttings to produce transplantable actively growing shoots (aka Active Shoot Propagation or “ASP”). The stool may produce multiple shoots after each harvest and provide several rotations depending on stool health. Move plants out of the domed flat when they have finished producing ASP shoots then grow them to planting size. Repot them as needed to prevent root binding.
Transplanting ASP Shoots:
Cut the shoots from the rootling stools with a clean, sharp razor when they start touching the dome. The best rootable softwood shoots are typically soft, playable and non-lignified.
Actively growing shoot tips (ASP) should include the meristematic tip with at least 3 leaves and a total shoot length at least 1" long. The stem should feel soft and pliable as lignified stems may not root. Ideally, the largest leaf should be at least 1" in length. Sometimes a small amount of sand can be applied around the ASP shoot base to help secure it in the cell.
The new ASP shoots should strike roots within 5 to 10 days. A gentle tug on the shoot may indicate root strike. It is acceptable to use a screwdriver to lift out a shoot within the first 12 days for inspection. Sometimes the previous leaves turn a reddish color indicating poor rooting conditions but the growing meristem should always appear healthy and vigorous.
After 20 days, most shoots could be cut and replanted, or the entire cell hardened off by pruning the tops and transplanted outdoors when new buds are developing. See photos: 2017 Open4st TE Rootling Photos, 2017 Open4st TE ASP Photos
this related worksheet, 2020RootlingASP.
Growing aspens under fluorescent lights produces less lignified shoots compared to greenhouse grown stock. The material can be "hardened" by cutting the stems to about 2" height, leaving several leaves to re-generate new growth from the residual leaf buds. It may also help to direct a light fan across the plants during the light period to emulate outdoor conditions. Be sure to watch soil moisture during this time. The stock should be ready for outdoor transplanting after growing about 2" of new growth, then store the flats in a shaded area for about 2 days before planting in an irrigated nursery.
T5 vs florescent light observations: Standard florescent lights are not as bright as T5 lights but may produce less lignified softwood ASP shoots that are easier to strike roots. However, the stronger T5 lights should produce a healthier plant that can be more suited to outdoor transplanting. Perhaps stools should be started with the T5 lights at 10" from the plant tops to produce less lignified shoots then grow the shoots with the lights at 6" from the tops to produce good roots. More research is needed to understand optimal indoor rootling propagation.
Table 4 describes a hypothetical rootling ASP rampup scenario under optimal conditions.
Table 4. Hypothetical Rootling with ASP Rampup Scenario