Physiological and Environmental Factors Affecting Shoot Tissue Boron Concentration of Pansy (Viola x wittrockiana), Petunia (Petunia x hybrida), and Gerbera (Gerbera jamesonii) Plugs.
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Date
2008-01-02
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Abstract
The overall objectives of these studies were to characterize and determine the causes of abnormal growth observed in pansy (Viola x wittrockiana), petunia (Petunia x hybrida), and gerbera (Gerbera jamesonii) plug production. Observed symptoms included distorted, curled and thickened leaves, abortion of apical meristems and proliferation of lateral shoots. Symptoms have been attributed to a calcium (Ca) or boron (B) deficiency. Calcium and B deficiencies were induced; plants deficient in Ca became discolored and eventually necrotic, while symptoms on plants deficient in B were similar to those observed in plug production.
It is improbable that insufficient B is the cause of B deficiency; growers use complete liquid fertilizer at every irrigation. High substrate pH causes B in the substrate to be unavailable to the plant. When germination substrate was incorporated with four increasing rates of dolomitic limestone, substrate pH increased and the shoot tissue concentration of B decreased. Plants take up B passively through the transpiration stream; therefore B uptake is linked to the rate of transpiration. Plants were exposed to 3 degrees of drought stress either by drying the substrate or the use of polyethylene glycol. Shoot concentrations of B were not effected by either drought stress treatment. Abscisic acid was applied as a foliar spray or substrate drench, each at 2 different concentrations, to decrease transpiration. Abscisic acid resulted in a decrease of both transpiration and shoot B concentration.
High relative humidity (RH ) can also decrease plant transpiration; plug production requires elevated levels of RH to ensure germination and to maintain hydration of young seedlings. Plants were grown in ambient or high RH; plants grown in high RH had lower shoot tissue concentrations of B. To attempt to counteract the effect of high RH, air flow was increased on a constant basis. Providing constant airflow did not increase transpiration or shoot tissue concentration of B.
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Hoagland's, Hydroponics, Nutrient deficiency
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Degree
PhD
Discipline
Horticultural Science
