The purpose of this comprehensive study was to investigate the effects of silicon-based fertilizer applications in promoting host-plant resistance to certain piercing-sucking insects feeding on horticultural/floricultural crops. Silicon is a major component of every terrestrial environment and may be present at low concentrations when growing horticultural/floricultural crops in greenhouse production systems. It has been hypothesized that using silicon-based fertilizers may promote host plant resistance in greenhouse-grown crops due to a silicon deficiency associated with low monosilicic acid concentrations in nutrient and hydroponic nutrient solutions.
In order to evaluate the effects of silicon-based fertilizers on phloem-feeding insects, a silicon determination procedure, the 'modified Hallmark' procedure, was developed specifically designed to assess total silicon concentrations (mg kg-1 Si) in plant tissues. The 'modified Hallmark' silicon determination procedure proved to be inexpensive, consistent, and reliable, in its assessment of total silicon concentrations in plant tissues. The 'modified Hallmark' procedure was compared to two different inductively coupled plasma-optical emission spectroscopy (ICP-OES) silicon determination procedures conducted by independent laboratories using two National Institute of Standards and Technology (NIST) reference materials; pine needles (NIST #1575) and peach leaves (NIST #1547), a rice straw standard (LSU#5), and five different horticulture/floriculture plant species. The 'modified Hallmark' silicon determination procedure commonly reported the highest silicon concentration values or within 15% of the two ICP-OES procedures. Furthermore, 10 horticulture/floriculture plant species were assessed using the 'modified Hallmark' procedure to establish baseline silicon concentrations when grown under greenhouse conditions and determined that zinnia, Zinnia elegans, and aster, Symphyotrichum novae-angliae plants accumulate substantial amounts of silicon (5,365 and 4,797 mg kg-1 Si respectively) compared to coral flower, Heuchera hybrid, and French marigold, Tagetes patula (556 and 625 mg kg-1 Si respectively). In addition, the 'modified Hallmark' procedure costs significantly less, approximately $50,000 less, when compared to ICP-OES procedures and equipment.
The 'modified Hallmark' silicon determination procedure allowed for correlations to be made linking insect pest performance, as indicated by insect life history parameters, to total plant silicon concentrations. The insect life history parameters of female egg load, size (mm), development time, (days), mean proportions of pupation (%), and mean proportions of adult emergence (%) were assessed from citrus mealybug and greenhouse whitefly pests feeding on coleus, poinsettia, and fiddleleaf fig plants. There appears to be no benefit of applying silicon-based silicon fertilizers to prevent population outbreaks of these insect pests feeding on these crops grown under greenhouse conditions. The accumulation properties of silicon in coleus, poinsettia, and fiddleleaf fig plant varied greatly ∼1,000 to 7,000 mg kg-1 Si) depending on the plant species and silicon rate treatment application. Coleus and poinsettia plants may be classified as silicon 'rejectors' (<5,000 mg kg-1 Si), and the fiddleleaf fig plants may be classified as silicon 'neutral' (5,000 to 30,000 mg kg-1 Si). It is apparent from the current study that silicon-mediated insect resistance may be dependent on the silicon accumulating properties of individual plant species; however, all of the plant species investigated in this comprehensive study did not accumulate sufficient amounts of silicon to result in any determinable silicon-mediated pest resistance.
Applications of silicon-based fertilizers to coleus, poinsettia, and fiddleleaf fig did not increase plant growth and development parameters such as moisture content (g), plant height (cm), and the number of mature leaves. The results of these studies clearly demonstrate that applications of silicon-based fertilizers to certain plant species including coleus, poinsettia, and fiddleleaf fig plants do not inhibit feeding of certain phloem-feeding insect pests such as citrus mealybug and greenhouse whitefly. Although, silicon may function as a protective or mechanical barrier associated with increased epidermal leaf thickness/toughness and strengthening cell walls in certain plant species, these effects are not universal. The proposed hypothesis that the presence of silicon in plant tissues inhibits insect feeding, and thus, development and reproduction, particularly phloem-feeders with piercing-sucking mouthparts such as citrus mealybug and greenhouse whitefly was not supported by the current study. The use of supplemental silicon-based fertilizers applied to greenhouse-grown crops do not provide host-plant resistance to certain insect pests.
|Advisor:||Cloyd, Raymond A., Swiader, John M.|
|School:||University of Illinois at Urbana-Champaign|
|School Location:||United States -- Illinois|
|Source:||DAI-B 70/02, Dissertation Abstracts International|
|Subjects:||Organismal biology, Horticulture|
|Keywords:||Citrus mealybug, Euphorbia pulcherrima, Greenhouse whitefly, Greenhouse-grown crops, Planococcus citri, Plant silicon, Poinsettia, Silicon, Silicon-based fertilizer, Trialeurodes vaporariorum|
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