Manipulating air and root-zone temperature for energy-efficient floriculture crop production

Given the high energy costs for greenhouse floriculture production, growers are constantly searching for more energy-efficient methods of production. For example, some growers will lower greenhouse air temperature set points or grow crops in unheated high tunnels (HTs) or outdoors in order to minimize or eliminate heating costs. Unfortunately, development can be delayed and morphology can be altered if the mean daily air temperature (MDT) is reduced. We proposed that reducing MDT in combination with root-zone heating (RZH) could be an energy-efficient method for producing high-quality floriculture crops without significant delays. Unheated HT and unprotected outdoor production are very low-cost systems for bedding plant production, but little information is available on crop developmental and morphological effects. The objectives of this study were, therefore, to quantify growth and development of 1) red poinsettia cultivars finished under reduced MDT in combination with RZH (Experiment 1); 2) several petunia cultivars and recombinant inbred lines grown under reduced MDT in combination with RZH (Experiment 2); and 3) cold-tolerant and cold-intermediate annual bedding plants grown in an unheated HT or unprotected outdoor growing area with or without an acclimation period (Experiment 3). In Experiments 1 and 2, time to flower decreased with increasing root-zone temperature across species and cultivars. Overall, high-quality poinsettias can be produced without delay if MDT is reduced by 5 °C, but a RZH set point of ≥24 °C is employed during the finish stage. Similarly, MDT can be reduced to 15 °C for petunia production when a RZH set point of 27 °C is utilized. In Experiment 3, flowering of all species was delayed when plants were grown outdoors compared to in the HT. However, high-quality annual bedding plants could be produced outdoors, depending on species, given the increased daily light integral (DLI) and air movement to keep plants compact. When plants were given a one-week acclimation period in the HT prior to outdoor production, almost all species were delayed less than 1 week compared to those grown in the HT only. When producing crops outdoors, growers must be aware of the risk of delay or crop loss due to extreme weather. Generally, high-quality floriculture crops can be produced with minimized cost for heating in a greenhouse with reduced MDT in combination with RZH, as well as in an unheated HT or outdoors, depending on species and weather conditions

Transcriptome Analyses of Mosaic (MSC) Mitochondrial Mutants of Cucumber in a Highly Inbred Nuclear Background.

Cucumber (Cucumis sativus L.) has a large, paternally transmitted mitochondrial genome. Cucumber plants regenerated from cell cultures occasionally show paternally transmitted mosaic (MSC) phenotypes, characterized by slower growth, chlorotic patterns on the leaves and fruit, lower fertility, and rearrangements in their mitochondrial DNAs (mtDNAs). MSC lines 3, 12, and 16 originated from different cell cultures all established using the highly inbred, wild-type line B. These MSC lines possess different rearrangements and under-represented regions in their mtDNAs. We completed RNA-seq on normalized and non-normalized cDNA libraries from MSC3, MSC12, and MSC16 to study their nuclear gene-expression profiles relative to inbred B. Results from both libraries indicated that gene expression in MSC12 and MSC16 were more similar to each other than MSC3. Forty-one differentially expressed genes (DEGs) were upregulated and one downregulated in the MSC lines relative to B. Gene functional classifications revealed that more than half of these DEGs are associated with stress-response pathways. Consistent with this observation, we detected elevated levels of hydrogen peroxide throughout leaf tissue in all MSC lines compared to wild-type line B. These results demonstrate that independently produced MSC lines with different mitochondrial polymorphisms show unique and shared nuclear responses. This study revealed genes associated with stress response that could become selection targets to develop cucumber cultivars with increased stress tolerance, and further support of cucumber as a model plant to study nuclear-mitochondrial interactions