Controlled-temperature Treatments with Low-cost, Off-the-shelf Equipment for Bud or Seed Forcing Experiments

in HortScience

Inexpensive plug-and-play temperature controllers have recently become available. These allow a chest freezer to be programmed easily to hold a desired set point across a range of biologically relevant temperatures. Installation can be completed in a few minutes using consumer-grade chest freezers. We used these temperature controllers to create five temperature-controlled chambers at 12, 14, 16, 18, and 20 °C. We demonstrated the use of these controlled-temperature chambers with two biologic assays: floral budbreak of peach [Prunus persica (L.) Batsch] stem cuttings and germination of sunflower (Helianthus annuus L.) seeds. We used the budbreak and germination rates at multiple temperatures to estimate base temperatures and thermal time requirements for development.

Contributor Notes

Funding for this project was provided from the Clemson University Creative Inquiry program and a grant to Douglas Bielenberg and Ksenija Gasic from the U.S. Department of Agriculture Specialty Crop Block Grant Program (agreement AM170100XXXXG034) through the South Carolina Department of Agriculture.

We thank Rosa Kome and Marcellus Washington for their invaluable assistance with data collection.

Corresponding author. E-mail: dbielen@clemson.edu.

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    Forty-eight-hour time course of temperature recordings (at 10-min intervals) from chest freezers with installed ITC-308 Outlet Temperature Controllers (Inkbird Tech. Co., Ltd., Shenzhen, P.R. China). Chambers were not opened during the 48-h period. Temperature set points and cooling differentials set as described in Materials and Methods.

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    Peach floral budbreak (left) or sunflower seed germination (right) fraction at constant forcing temperatures. The gray line indicates the median budbreak or germination.

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    Rate of median floral budbreak (left) or median sunflower seed germination (right) at constant forcing temperatures. Regression lines are extended to the horizontal axes to indicate the x-axis value where the development rate is estimated to be zero (Tb, indicated by arrows).

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