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Title: Elevated relative humidity increases the incidence of boron deficiency in bedding plants

Author
item KRUG, BRIAN - University Of New Hampshire
item WHIPKER, BRIAN - North Carolina State University
item MCCALL, INGRAM - North Carolina State University
item Frantz, Jonathan

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2013
Publication Date: 3/1/2013
Citation: Krug, B.A., Whipker, B.E., McCall, I., Frantz, J. 2013. Elevated relative humidity increases the incidence of boron deficiency in bedding plants. HortScience. 48:311-313.

Interpretive Summary: High relative humidity is believed to lead to lower concentrations of the essential element boron in plants, but the link has not been conclusively established. In greenhouses, it is common to mist or fog young plants or seedlings to avoid plant stress, but this practice leads to elevated humidity. As this practice has increased with seedling production, so have the observations of boron deficiency in a few highly susceptible species including pansy, petunia, and gerbera. These crops were grown experimentally with high (about 100% relative humidity) and ambient (about 75% relative humidity) conditions. Results showed that increased relative humidity lead to less water loss in those seedlings and those plants also had less boron in their tissue. This provides convincing evidence that the distorted growth observed in pansy petunia and gerbera plug production is the result of limited B caused by excessive humidity.

Technical Abstract: High relative humidity (RH) can cause lower concentrations of B accumulating in plants. The common greenhouse practice of controlling excess temperatures by applying mist irrigation to youngplants (plugs) results in elevated RH levels. Reports of boron (B) deficiency have become more prevalent over the last few years in pansy (Viola ×wittrockiana), petunia (Petunia ×hybrida), and gerbera (Gerbera jamesonii) plug production, especially with plugs grown in high heat and humidity conditions of summer. 'Dynamite Yellow' pansy, 'White Storm' petunia, and 'Festival Apricot' gerbera plugs were grown in high or ambient RH conditions to determine the effect. Results indicate that an increase in RH decreased the amount of water the plant loses due to transpiration resulting in lower concentrations of B in shoot tissue. In Expt. 1, B concentrations in leaf tissue were 9.43, 10.56, and 17.81 mg per L in pansy, petunia, and gerbera plants, respectively, grown in high RH conditions. These values were significantly lower than pansy, petunia, and gerbera plants grown in ambient RH conditions (19.94, 25.49, and 42.71 mg per L, respectively). Similar trends were observed when the experiment was repeated. This provides conclusive evidence that the distorted growth observed in pansy petunia and gerbera plug production is the result of limited B caused by excessive humidity.