Date of Award

2018-01-01

Degree Name

Doctor of Philosophy

Department

Environmental Science and Engineering

Advisor(s)

Jorge L. Gardea-Torresdey

Abstract

Sweetpotato [Ipomoea batatas (L.) Lam.] is widely cultivated in many countries worldwide. The world production of sweetpotato is around 127 billion tons and it is ranked seventh in the world as a staple food. After harvesting, sweetpotato storage roots are treated with fungicides to prolong shelf life. Lignin plays an important role in the conservation of the storage roots. One of the practices to activate the lignification pathway is called “curing process.” The roots are placed under 80% relative humidity at a temperature of 29 ºC for a period of 7 to 15 days, followed by a cooling period at 10 - 18 ºC. Until recently, storage roots were protected against pathogens by using the fungicide dicloran, but foods with dicloran residues are no longer accepted in many markets including infant foods, organic foods, and exports. Thus, other fungicides, including copper, have been used. Thus far, only ionic copper compounds had been utilized to protect the plants against the fungus diseases in crop fields; therefore, new copper products—including the nano forms—may have great potential to be used to preserve the quality of the plants in open fields and the roots in shelves. Currently, there is a lack of information concerning the interaction of copper-based engineering nanomaterials (ENMs) with the skin components of the roots, the lignin content, and the interaction with the physiological process like chlorophyll content, photosynthesis, and carbohydrates production. The objectives of this study were: (1) to determine the effects of curing and lignin content of the periderm in the retention of copper ions/particles, and (2) to study the physiological effects of copper oxide (CuO) nanoparticles or compounds in sweetpotato plant growth and production. This study was performed in two phases. In phase I, commercial roots of Beauregard-14, low lignin content) and Covington (COV, high lignin content) were exposed to CuO nanoparticles (nCuO), bulk CuO (bCuO) and copper chloride (CuCl2) at the concentration of 0-125 mg/L, before and after curing. After treatment, root tissues were analyzed by inductively coupled plasma-optical emission spectroscopy (ICP-OES) or scanned with a two-photon microscope to study the possible penetration of Cu particles into the storage root tissues. At 25 mg/L, only bCuO showed higher Cu concentration in the periderm and cortex of B -14 (2,049 mg/kg and 76 mg/kg before curing; 6,769 mg/kg and 354 mg/kg after curing, respectively) and in cortex of COV (692 mg/kg before curing and 110 mg/kg after curing), compared with controls (p ≤ 0.05). In medulla, the most internal tissue, only B-14 exposed to 125 mg/L bCuO showed significantly (p ≤ 0.05) more Cu before curing (17 mg/kg) and after curing (28 mg/kg), compared with control (p≤ 0.05).

In Phase II, slips from the two varieties were planted in plastic pots containing 3 kg of soil each amended with the three copper compounds at 25, 75, and 125 mg/kg and cultivated under full sun exposure. Gas exchange parameters, root production, and nutritional composition of the roots were evaluated at the physiological maturity of the plants. After harvesting, roots were classified by size and analyzed for nutrient element contents or changes in macromolecules.

The interaction of copper compounds with photosynthesis showed that the higher variance was due to differences in lignin content between varieties. The ICP-OES data showed no increase of Cu in medulla, except for B-14 plants exposed to CuCl2 at 125 mg/kg, which had 622% more Cu in medulla, compared with control (p ≤ 0.05). The fresh weight of B-14 storage roots was higher in plants exposed to bCuO at 75 and 125 mg/kg, compared with nCuO at 125 mg/kg, but there were no differences with control. The root length was increased by nCuO at 25 mg/kg in COV, compared with the other treatments.

None of the treatments affected the protein content in storage roots. The sugar content was significantly increased by 75 mg/kg nCuO by 140%, respect to the control (p ≤ 0.05). Starch was reduced by 71% in B-14 and by 80% in COV roots exposed to bCuO at 25 mg/kg). Additionally, at 125 mg/kg, bCuO and CuCl2 showed a reduced number of starch grains per sample, and most of them were misshaped. The prospective use of nCuO during root curing, plus the increase in sugar and root length on soil grown plants suggest that nCuO may represent a good alternative to protect sweetpotato plants during cultivation and increase the shelf life of the roots.

Language

en

Provenance

Received from ProQuest

File Size

94 pages

File Format

application/pdf

Rights Holder

Nestor Javier Bonilla Bird

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