Characterizing the regulation of development by temperature requires controlled exposure of replicate plants (whole or in part) to multiple temperature environments simultaneously. Experiments with seeds or other small plant segments can be performed on a thermal gradient table, which can generate many temperatures simultaneously (Welbaum et al., 2016). However, experiments involving larger plant parts, such as cut stems used in forcing experiments of woody perennials, require temperature control of a larger three-dimensional volume, such as an environmental chamber (Anzanello and Biasi, 2016; Primack et al., 2015). Inexpensive access to the number of environmental chambers needed for the parameterizing temperature response curves for development is not common and can limit the scope of experiments. Modifications of consumer-grade freezers or refrigerators to bypass built-in temperature controllers with programmable controllers have been used for a variety of applications, but require a minimum level of technical ability to wire and install safely (Hutten-Czapski, 2017). Newly available plug-and-play temperature controllers allow conversion of a standard chest freezer into a controlled-environment chamber in minutes, with no custom modification.
Our objective in this study was to demonstrate that inexpensive, easy-to-use temperature controllers are able to provide reliable set temperatures for the detailed observation of developmental rates in response to different temperature treatments. We used the observed developmental rates at 12, 14, 16, 18, and 20 °C to estimate a thermal time parameter (base temperature) for the development of two different developmental events: floral budbreak in peach [Prunus persica (L.) Batsch] and seed germination in sunflower (Helianthus annuus L.). Developmental rates were evaluated at the temperatures mentioned to avoid the confounding influence of chilling temperatures on peach floral bud development, which are most effective between 4 and 8 °C (Anderson et al., 1986). Floral budbreak in Prunus sp. is commonly assumed to have a base temperature for development of 4 °C, but this assumption has not been widely tested across diverse species or varieties (Anderson et al., 1986). Recent work demonstrated genotypic variation in the base temperature for vegetative budbreak within fruit tree species, demonstrating the need to develop methods to test our assumptions with widespread screening of germplasm (Anzanello and Biasi, 2016). A base temperature of 6.7 °C is often used in germination modeling in sunflower, but varieties have been shown to have lower base temperatures (Khalifa et al., 2000).
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AnzanelloR.BiasiL.A.2016Base temperature as a function of genotype: A foundation for modeling phenology of temperate fruit speciesSemin. Cienc. Agrar.3718111826
KhalifaF.M.SchneiterA.A.EltayebE.I.2000Temperature–germination responses of sunflower (Helianthus annuus L.) genotypesHelia2397104
PrimackR.B.LaubeJ.GallinatA.S.MenzelA.2015From observations to experiments in phenology research: Investigating climate change impacts on trees and shrubs using dormant twigsAnn. Bot.116889897
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ZhebentyayevaT.N.FanS.ChandraA.BielenbergD.G.ReighardG.L.OkieW.R.AbbottA.G.2013Dissection of chilling requirement and bloom date QTLs in peach using a whole genome sequencing of sibling trees from an F2 mapping populationTree Genet. Genomes103551