Author
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KRUG, BRIAN - University Of New Hampshire |
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WHIPKER, BRIAN - North Carolina State University |
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FONTENO, BILL - North Carolina State University |
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MCCALL, INGRAM - North Carolina State University |
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Frantz, Jonathan |
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Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/15/2010 Publication Date: 5/19/2011 Citation: Krug, B., Whipker, B., Fonteno, B., Mccall, I., Frantz, J. 2011. Incidence of boron deficiency in bedding plants caused by drought stress or abscicic acid application. Acta Horticulturae. 891:141-147. Interpretive Summary: Growers have reported boron (B) deficiency in pansy plug production with the incidence of the deficiency especially prevalent in the high heat and humidity conditions of summer. Past studies have reported that soil moisture has an impact on boron availability. To simulate drought conditions, pansy plants were grown in a peat based growth substrate that was allowed to dry down to 40, 30, or 20% container capacity (CC), 10 or 20 days after planting or in continuously dried conditions. Boron tissue concentration was not affected by any induced drought stress, with the exception of those allowed to dry to 40% CC 20 days after planting. To simulate drought stress, a growth regulator based on the hormone abscisic acid (ABA) was applied as a substrate drench or foliar spray at concentrations of 150 or 300 ppm to pansy plants 10 or 20 days after planting. All treatments resulted in lower tissue concentrations of B compared to an untreated control. Plants treated 10 DAS with a substrate drench at 300 ppm or a foliar spray of 150 ppm and plants treated 20 DAS with a foliar spray at both concentrations had a reduction of water uptake. Plants had less transpiration per leaf area when ABA was applied as a 300 ppm substrate drench 10 days after planting and as foliar spray at both concentrations at either application time. The lower B tissue concentrations coupled with lower transpiration rates were similar to circumstances in greenhouse production of fall pansy crops. This research helps explain the observation of B deficiency most commonly appearing in August when high temperatures and relative humidity cause the plants to transpire less. Technical Abstract: Growers have reported boron (B) deficiency in pansy (Viola ×wittrockiana) plug production, specifically in plugs grown in the high heat and humidity conditions of summer. Past studies have reported that soil moisture has an impact on boron availability. To simulate drought conditions, 'Dynamite Yellow' pansy plants were grown in a peat based substrate that was allowed to dry down to 40, 30, or 20% container capacity (CC), 10 or 20 days after sowing (DAS) or on a continual basis. Boron tissue concentration was not affected by any induced drought stress, with the exception of those allowed to dry to 40% CC 20 DAS. To simulate a physiological response to drought stress, exogenous abscisic acid (ABA) was applied as a substrate drench or foliar spray at concentrations of 150 or 300 mg L-1 to 'Dynamite Yellow' pansy plants grown in a peat based substrate 10 or 20 DAS. All treatments resulted in lower tissue concentrations of B compared to an untreated control. Plants treated 10 DAS with a substrate drench (300mg L-1) or a foliar spray (150 mg L-1) and plants treated 20 DAS with a foliar spray (150 or 300 mg L-1) had a reduction of transpiration. Plants had lower ratios of transpiration/leaf area when ABA was applied as a 300 mg L-1 substrate drench 10 DAS and as foliar spray at both concentrations at either application time. The lower B tissue concentrations coupled with lower transpiration rates were similar to circumstances in greenhouse production of fall pansy crops. Boron deficiency is most common in August when high temperatures and relative humidity cause the plants to transpire less. |
