Research Update

 

Jason Smith and Jeff Gillman

 

 

 

As we move from spring into summer it is time to once again review the research articles from the past spring that are of interest to the nursery industry.  The past few months have yielded several articles that provide beneficial information. In particular, there have been articles dealing with growth regulation of Russian sage during production, use of compost as a media amendment for container production, mulching affects on water use in containerized plants, micropropagation of Echinacea, cultivar specific effects of mycorrhizal fungi on rooting of miniature roses, and photodegradation of ferric ethlelenediamine-tetraacetic acid (FeEDTA) in commercial soluble fertilizers.

            As we provide these reports, we ask you to remember that we are reporting research conducted by others and neither endorse nor refute their work. If you have any questions about the research we are reporting, please look at the original article (citations are provided at the end of the reports). Several of these reports were based on research done in climates very different from Minnesota, so please keep this in mind. In some reports there may be use of compounds that are inconsistent with manufacturers’ labels. We strongly discourage the use of any compound in a way that does not agree with the manufacturers’ labels.

  • Plant growth retardants (PGRs) are often used to discourage rapid, leggy growth which requires intensive maintenance in nursery production. Several brands are on the market for use, but how does the grower decide what is the most efficient way to use retardants since the labels give a range of concentrations? In this study, the authors attempt to answer this question by treating nursery and greenhouse grown Russian sage (Perovskia atriplicifolia Kar.) with PGRs (Cutless, Sumagic, B-Nine/Cyclocel, and Pistill at various concentrations). Three production regimes were tested: (1) plants in 4 inch pots grown in the greenhouse and half transplanted into the landscape at 6 weeks after treatment (WAT). The PGRs were applied as a foliar spray when the new growth reached 1 inch. Growth index (GI) was determined at 2 week intervals starting at 2 WAT and half of the plants were planted in the landscape at 6 WAT to determine the persistence of treatments in landscape plantings. Growth regulation by Cutless was inconsistent in the greenhouse studies.  The results obtained  also suggest that PGR effectiveness is greatest with greenhouse grown plants and PGR combinations (B-Nine/Cyclocel) may be more effective 1. 
  • Due to increased cost and environmental concerns, alternatives to peat-based potting media are needed. In this article, the authors have investigated the use of compost (biosolids and yard trimmings) as an amendment of commercial peat or coir-based media and its affect on the growth of two subtropical perennials. Peat- and coir-based soilless mixes, available commercially, were amended with 25%, 50%, 75% or 100% compost (made up of biosolids and yard trimmings, 1:1, by weight). Young plugs of cat whiskers (Orthosiphon stamineus) and  angelonia (Angelonia angustifolia) were planted in the respective media in 1.3 gallon pots. The media were evaluated for pH, electrical conductivity (EC), percent moisture, total carbon (C), and total nitrogen (N). Plant growth and development was measured 8 weeks after transplanting by evaluating primary stem length, dry weight, flower number and chlorophyll content. As the percentage of compost increased, the pH, EC, % N,  and %C increased and moisture content decreased. Growth decreased when the plants were grown in media with  high percentages (75-100%) of  compost. Flowering was not affected by any of the treatments and the plants were visually acceptable when grown in all but 100 % compost.2
  • Hanging baskets of annuals are popular addition to many landscapes, however they require frequent watering. Virginia Lohr and Caroline Pearson-Mims at Washington State University assessed the effectiveness of mulching on the water use of basket-grown Impatiens wallerana ‘Impulse Rose’. In this study, the authors grew transplants in 7.5 inch azalea pots, mulched with either pine bark mulch or sphagnum moss. The controls contained no mulch. Both mulches reduced frequency of irrigations when the plants were small (when the canopies didn't cover the surface of the soil). Although mulching educed the need for watering, it had no effect on plant growth or flowering.3
  • Purple coneflower (Echinacea spp.) has recently become very popular as an ornamental and for medicinal use. This popularity has resulted in the need to develop rapid propagation techniques to facilitate availability of elite germplasm. In this study the author, James Harbage at South Dakota State University  describes a method for rapid miropropagation of purple coneflower . Seedling and stem explants were initially taken from greenhouse grown stockplants. The explants were treated with 15 % household bleach with 0.1% Tween 20®  followed by rinsing in sterile deionized water  for 30 seconds. The explants were placed on sterile medium containing Murashige and Skoog (MS) minerals, myoinositol, thiamine HCl, bezyladenine (BA), sucrose and Difco Bacto agar. Aseptic cultures were isolated from explants via four methods: (1) intact, (2) after removal of the outer seedcoat, (3) after removal of the outer seedcoat and integument layer and (4) after removing the outer seedcoat, integument layer and endosperm layer. Data was taken at 4 weeks on the number of shoots produced and the percentage of contamination. Several variables were measured in other experiments where the author looked at the effect of cytokinin, mineral composition and concentration on shoot formation , shoot formation responses to subculture frequency, and auxin, light and temperature influences on rooting. The results indicate that high contamination rates can be expected from shoot tip explants, but not nodal segments. Contamination decreased with the amount (number of layers) of seedcoat removed. Cytokinins reduced the number of roots, but increased the number shoots. The concentration of the minerals affected the shoots with half strength MS increasing shoot counts and leaf size being greater on full strength MS. Reducing the number of subcultures from 4 to 2 increased shoot formation. Auxins did not promote root formation on E. purpurea (no rooting occurred on the other species) and light and temperature had no effect. The author suggests with future improvements in rooting techniques, the methods described here could be useful for rapid micropropagation of this genus.4  
  • Root colonization by VA mycorrhorizal fungi (VAMF) is known to be most beneficial when the roots are colonized early in their formation. In this study, the author, C.F. Scagel at the U.S.D.A. Horticultural Crops Research Laboratory in Corvallis, Oregon, attempted to evaluate the effectiveness of inoculating miniature rose cuttings of different cultivars with VAMF .Two node cuttings from 5 different cultivars were taken and sanitized by dipping in 10% bleach for 20 minutes then rinsed with water. The cuttings were given the following treatments: no VAMF or hormone (control), a hormone treatment (1:10 dilution of Woods Hormone Solution) and no VAMF (HOR), and a commercial inoculum of VAMF (Glomus intraradices) and a hormone treatment (1:10 dilution of Woods Hormone Solution) (HOR-VAM). At 28 days after the start of the experiment, the cuttins were harvested and were rated as rooted, callused, or dead. The number of primry and secondary lateral roots was counted for each cutting.  The fresh and dry weights of both roots and shoots were measured. The percentage of root length with evidence of colonization by VAMF was estimated. The number of cuttings with roots increased on two cultivars that are normally slow to root when treated with both hormone and VAMF. The number of cuttings with roots and number of roots per cutting increased on the other three cultivars with this treatment (compared to hormone alone). The author points out however, that the increases in root initiation and root growth were no always associated with colonization of roots with VAMF.5
  • Soluble fertilizers are often stored in many different places in nurseries. How do these conditions affect their components and ultimately effectiveness ? Joseph Albano and William Miller investigated photodegradation of FeEDTA, iron chelate, a common component of commercially produced soluble fertilizers. In this study, the authors the authors prepared 100X stock solutions of commercial fertilizers for soilless media and placed the solutions in 1L high density polyethylene bottles. The fertilizers were irradiated (with fluorescent plus incandescent light)  and the controls were non-irradiated. The solutions were analyzed after 10 days. The results obtained show that irradiation resulted in a loss of FeEDTA, a loss of soluble Fe and formation of a tan precipitate made mostly of Fe (with a little Mn, and Zn).This did not occur in non-irradiated samples. On average, 88% of total Fe, 12 % of total Mn, and 12% of total Zn was lost due to irradiation. The Fe:Mn ratio changed from 2:1 in non-irradiated solutions to 1:4 in irradiated solutions. The authors recommend that soluble fertilizers be stored in fertilizer tanks that are impervious to light to avoid loss of expensive and important components of these fertilizers.6

 

 

1  Burnett, S.E., G.J. Keever, C.H. Gilliam, and J.R. Kessler, Jr. 2001. growth regulation

of Russian sage during greenhouse and nursery production. Journal of Environmental     Horticulture 19(1): 24-28.

2 Wilson, S.B., P.J. Stoffella and D.A. Graetz. 2001. Use of compost as a media 

       amendment for containerized production of two subtropical perennials. Journal of

       Environmental Horticulture 19(1): 37-42.

3 Lohr, V. I., and C.H. Pearson-Mims. 2001. Mulching reduces water use of containerized

       plants. HortTechnology 11(2): 277-278.

4 Harbage, J.F. 2001. Micropropagation of Echinacea angustifolia, E. pallida, and E.

       purpurea from stem and seed explants. HortScienece 36(2): 360-364.

5 Scagel, C.F. 2001. Cultivar specific effects of mycorrhizal fungi on the rooting of

       miniature rose cuttings. Journal of Environmental Horticulture. 19(1): 15-20.

6 Albano, J.P. and W.B. Miller. 2001 Ferric ethylenediamine-tetraacetic acid (FeEDTA)

       photodegradation in commercially produced soluble fertilizers. HortTechnology

       11(2): 265-267.