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  • Author or Editor: Lawrence E. Datnoff x
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The objectives of these studies were to evaluate the effects of silicon on drought and shade tolerance of st. augustinegrass (Stenotaphrum secundatum). Studies were conducted during 2001 in a glasshouse at the University of Florida Turfgrass Research Envirotron in Gainesville. For both drought and shade evaluations, calcium silicate slag (CaSiO3) was pre-incorporated into pots with commercial potting soil at the rate of 3.36 kg·ha-1 (0.069 lb/1000 ft2). `FX-10' and `FHSA-115' st. augustinegrass were planted into 15.2-cm-diameter × 30.5-cm-deep (6 × 12 inches) plastic pots for the drought study and subjected to minimal irrigation. Under severe drought stress, silicon-amended plants had better responses than non-amended plants. Little improvement was seen under moderate drought stress. `Floratam' and genotype 1997-6 were placed under full sunlight or 50% to 70% shade. There was no benefit from use of silicon under shaded conditions. These findings suggest that silicon might provide improved tolerance to st. augustinegrass under severe drought stress.

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Corky root (CR) of lettuce (Lactuca sativa L.) is caused by the bacterium Rhizomonas suberifaciens. Current management strategies involve the use of resistant cultivars and crop rotation. The use of transplants as a method to grow CR-susceptible cultivars in CR-infested fields was recently demonstrated. The objective of this study was to evaluate corky root destruction of root systems of direct-seeded and transplanted lettuce. Direct seeded, and three and five week old transplants of CR susceptible `Shawnee' and CR resistant `South Bay' crisphead lettuce were grown in a naturally CR-infested field. Root systems were evaluated at head harvest maturity. When direct seeded, South Bay developed 104% more total lateral root length than did Shawnee. When transplanted at three and five weeks, South Bay developed 50% and 61% more total lateral root length than Shawnee, respectively. Total lateral root length for Shawnee transplanted at five weeks was 100% greater than direct seeded Shawnee. Comparatively, total lateral root length for South Bay transplanted at five weeks was 58% greater than direct seeded South Bay. Tap root lengths and dry weights were not different among planting systems. Transplanting is a possible method for reducing the impact of CR on lettuce lateral root development.

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Experiments were conducted during two different time periods to determine if hybrid phalaenopsis orchid (Phalaenopsis spp.) liners accumulate silicon (Si) and if this element can affect liner growth. A total of 800 liners were evaluated and Si fertilization was performed by applying potassium silicate (KSiO3) as a drench with three treatments (0.5%, 1.0%, and 2.0% v/v) and a control (water, no Si fertilization). The application of KSiO3 affected overall growth of phalaenopsis orchid liners, where Si content of the plant ranged from 0.5% to 1.7%. Overall, Si applied at 0.5% and 1.0% increased fresh weight and dry weight (DW) and at 1.0% Si significantly increased DW of root, shoot, and whole plant over the control. Increases in DW ranged from 27% up to 118%. Results from the second experiment were similar. Other plant parameters evaluated such as leaf number and size, root number, and length were unaffected by Si application. Although leaves of phalaenopsis orchid liners treated with Si appeared darker green when compared with the control, no significant differences were observed in chlorophyll content of leaves. Reduced growth was observed when 2.0% Si was applied affecting Si tissue concentrations and substrate electric conductivity. The data obtained from this study indicate that hybrid phalaenopsis orchid liners are Si accumulators and that this element influences their growth. Further studies are warranted to address the long-term effects of Si fertilization on the complete life cycle of hybrid phalaenopsis orchids.

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