Optimizing herbaceous annual cutting physiology, morphology, and rooting with supplemental light during propagation

Christopher J Currey, Purdue University

Abstract

Propagative material for the U.S. alone has a wholesale value of over $439 million USD. Energy costs are one of the largest expenses in greenhouse production and, therefore, producers of rooted cuttings are interested in minimizing production time. Growth and development of adventitious roots on cuttings is strongly influenced by temperature and light, while subsequent growth and development of rooted cuttings is impacted by the environmental conditions experienced during propagation. Cuttings are propagated in winter and spring when the ambient solar and greenhouse photosynthetic daily light integrals (DLI) are at seasonally low levels. There is limited, but promising, evidence that increasing the DLI during propagation of cuttings increases root development and growth of cuttings of annual bedding plants. The specific objectives of this research are to identify the growth, morphological, and physiological responses of un-rooted cuttings to varying DLIs and supplemental light quality. Three research goals were established to support my objectives: 1) identify species-specific responses from a broad group of vegetatively propagated annuals to DLI during root development; 2) characterize the effect of DLI during root development on biomass accumulation and allocation, photosynthesis, and carbohydrates of cuttings; and 3) quantify the effect of supplemental light source and quality during root development on cuttings. Increasing the DLI during propagation with supplemental lighting increased root and shoot growth of nine herbaceous annuals by up to 1137% and 384%, respectively. Additionally, the quality of rooted cuttings, as assessed by the quality index, increased for nearly each of the nine species used in the study by up to 960% (Diascia). Further studies showed increasing the DLI during root development enhanced biomass accumulation and altered biomass allocation of Impatiens, Pelargonium, and Petunia by increasing the root mass ratio by up to 195% (Petunia), while starch concentrations increased by up to 946% (Impatiens) with DLI. Additionally, I found that net photosynthesis (Pn) of Impatiens cuttings could increase by up to 150% and 250%, respectively, as DLI increased by ≈6 or 13 mol·m-2·d-1, respectively. Lastly, there were few significant morphological or physiological differences among rooted cuttings of Impatiens, Pelargonium, and Petunia cuttings propagated under HPS lamps or different LEDs, as well as for flowering plants grown from cuttings propagated under the different supplemental lighting treatments. By identifying the growth and physiological adaptations of herbaceous stem tip cuttings of annual bedding plant species to DLI and supplemental light quality during root development, the aims of the research are two-fold. The first is to provide insight into the physiological mechanisms related to root growth and DLI during propagation. Secondly, improve the quality of rooted cuttings while increasing the efficacy and efficiency of environmental and cultural inputs in greenhouse production.

Degree

Ph.D.

Advisors

Lopez, Purdue University.

Subject Area

Horticulture|Agriculture|Plant sciences

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