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United States Department of Agriculture

Agricultural Research Service


Location: Application Technology Research

2012 Annual Report

1a. Objectives (from AD-416):
Objective 1: Evaluate plant nutritional requirements to optimize production and enhance quality. Sub-objective 1a: Elucidate the optimal tissue concentration of P and B in different light environments for major production species and how their susceptibility to foliar and root pathogens are influenced by nutrient status and light. Sub-objective 1b: Determine the uptake, accumulation, and potential benefit of silicon in ornamental crops and explore the potential for its use as a buffer to Cu toxicity and an alternative approach to pathogen control. Objective 2: Develop new and/or improved methods to detect, quantify, and manage biotic and abiotic stresses in ornamental crops grown in soilless and/or hydroponic greenhouse culture. Sub-objective 2a: Evaluate the use of existing non-destructive sensor technology and develop new molecular probes to measure and predict the impact of biotic and abiotic stresses on ornamental crops. Sub-objective 2b: Improve the Virtual Grower software model to enable growers to optimize their production systems by making more informed economic decisions about energy use, plant growth, pest management, and other production inputs. Objective 3: Evaluate existing and alternative growth medium amendments to determine the potential to deliver Si and buffer pH without negatively impacting beneficial microorganisms or crop growth.

1b. Approach (from AD-416):
Impatiens, geranium, vinca, and zinnia will be grown in media amended with different concentrations of phosphorus and boron under different light environments to determine optimum supply and tissue concentrations of these nutrients. Plants containing different amounts of these nutrients will then be inoculated with Pythium, Phytophthora, Botrytis, and powdery mildew to determine host susceptibility. These same plant species will also be grown with supplemental silicon in the fertilizer solution or incorporated into the substrate as rice hulls or Si-containing slags, and inoculated with the same pathogens or expose them to elevated Cu concentrations in the rootzone to determine if Si plays a role in a plant’s ability to withstand pathogen attack and Cu toxicity. Plants grown in different amounts of light and exposed to the aforementioned pathogens will be monitored with various sensors (e.g. digital cameras, infrared temperature probes, fluorometers, chlorophyll meters) and molecular tools to detect initial onset of stress symptoms. Finally, the production methods developed within these tests can be incorporated into the existing computer decision support software Virtual Grower to help growers make decisions in crop management.

3. Progress Report:
Alternative root substrate materials in soilless media systems were evaluated for their value in the production of floricultural and nursery crops. Focus for this year was on: 1) determining the potential of wheat straw (WS) to function as a plant growth regulator (PGR) in bedding plant production, and 2) to study the function of biochar, added to commercial sphagnum peat:perlite growing media, to moderate nutrient supply and retention of the major elements nitrogen (N), phosphorus (P), and potassium (K). Four experiments evaluating the response of plants to phosphorus deficiency and subsequent recovery were completed using tomato as a model crop. Phosphorus deficiency results in plants reallocating resources to their root systems, resulting a larger percentage of root mass per plant and an increase in proteins that scavenge for P and shift N uptake from nitrate to ammonium forms. The shift in N form results in decreased root-zone acidity causing sudden pH decline. It was found that it takes about 4 days for photosynthesis to be impacted by P deficiency and 4 days after P re-supply, photosynthesis begins to return to normal rates. Plants experiencing P deficiency for a long enough time to display visible symptoms will never fully recover even after more than 2 weeks of P re-supply. Experiments were completed that evaluated the potential for a short-term Ultra Violet (UV) light exposure on seedlings to provide long-term plant growth regulation. The ornamental industry relies heavily on chemical growth regulators. Plants respond to UV light by decreasing photosynthesis and stopping cell division and expansion. In extreme cases (high UV doses), cellular damage or death can occur. Greenhouse environments are nearly devoid of UV light, making UV a potential tool to add to the production system to control growth. It was found that some species (e.g. spinach) are extremely sensitive to UV exposure while others barely respond (e.g. petunia). By varying the doses and potentially providing multiple low doses, plant growth could be controlled by non-chemical means. In cool climates such as the northern portion of the US, greenhouses are used to produce bedding plants during the winter months. These structures quickly deplete the production area in carbon dioxide (CO2), which is essentially plant food for photosynthesis. Adding CO2 is not often done in the floriculture industry, in part due to the belief that ornamental species do not respond to CO2. This is erroneous but the belief persists because plants become root-bound in production containers; with no more “sinks” to put the available CO2, plant photosynthesis is down-regulated. Seedling production in elevated CO2 was evaluated in controlled environments using traditional, commercial seedling trays. It was found that plants do respond to elevated CO2 by more rapid growth earlier in production. Potentially, this means that seedlings (and by extension, other phases of growth) could be produced more rapidly by using supplemental CO2. The additional CO2 consumed was found to be more than offset by the reduced need for heating fuel caused by the shorter production timeframe.

4. Accomplishments
1. Wheat straw soil amendment can act as a plant growth regulator. Researchers determined that wheat straw (WS), amended at up to 20-30% (v/v) can serve to limit plant growth and elongation of several bedding crops during the period of production without adversely affecting subsequent grow out or normal development (flowering). Initial retention and release of nitrogen (N), phosphorus (P), and potassium (K) was determined by repeated leaching of soilless growing media, peat-based substrate that was amended with biochar, in laboratory columns over time. These studies demonstrated that a variety of biochar materials, derived from various feedstocks, temporarily retained and then released N and P. Based on these results, whole plant growth studies were initiated, utilizing five crops, grown in soilless media amended with varying amounts of a biochar selected for its high P and silicon (Si) content. In these studies it became apparent that, although the readily available P and Si could be taken up by the plants, the longevity of its effectiveness as a fertilizer source (P) was limited to about four weeks. Plant tissue content of P was below the horticulturally acceptable level after this point. Follow up studies in market packs utilizing six representative crops, confirmed this short term fertilizer effect. Nursery-scale studies have been initiated late in the fiscal year utilizing the findings of the greenhouse trials in which two additional variables are being addressed; the addition of additional microelements and cultural practice modification to reduce leaching of the highly-soluble P. This research gives plant producers another tool to produce plants in a sustainable manner with less chemical inputs and reliance on overseas material while developing quality products for the floriculture consumer.

2. Ultra-violet light is a viable option for non-chemical plant growth regulation. We determined that ulta-violet (UV) light may be useful as a non-chemical plant growth regulator. Traditional floriculture crop production relies upon synthetic plant hormones or hormone derivatives for controlling plant growth and development. As a proof-of-concept, single doses of UV light were applied on seedlings of 10 crop species. After exposure, photosynthetic integrity, leaf expansion, and overall growth were evaluated. Immediately after exposure, photosynthesis decreased, and remained low 1 to 10 days. Leaf expansion also decreased leading to reduced overall growth in the following weeks. Depending on the species, UV light suppressed growth in a predictable manner similar to a chemical plant growth regulator (lower photosynthesis, decreased leaf expansion, changed height, no delay in flower development). This research provides a new method for non-chemical plant growth regulation.

Review Publications
Roberts, B.R., Linder, R.S., Krause, C.R., Harmanis, R. 2012. Humectants as post-plant soil amendments: effects on growth and physiological activity of drought-stressed, container-grown tree seedlings. Arboriculture and Urban Forestry. 38(1):6-12.

Locke, J.C., Altland, J.E., Bobak, D.M. 2011. Seedling geranium response to nitrogen deprivation and subsequent recovery in hydroponic culture. HortScience. 46(12):1615-1618.

Raikhey, G., Krause, C.R., Leisner, S. 2011. The Dahlia mosaic virus gene VI product N-terminal region is involved in self association. Virus Research. 159:69-72. DOI:10.1016/j.virusres.2011.04.026.

Frantz, J., Kandahar, S., Leisner, S. 2011. Silicon differentially influences Cu toxicity response in silicon-accumulator and non-accumulator species. Journal of the American Society for Horticultural Science. 136:329-338.

Zellner, W., Frantz, J., Leisner, S. 2011. Silicon delays tobacco Ringspot virus systemic symptoms in Nicotiana tabacum. Journal of Plant Pathology. 168(15):1866-1869. DOI:10.1016/j.jplph.2011.04.002.

Last Modified: 06/26/2017
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