Date of Award

2019-01-01

Degree Name

Doctor of Philosophy

Department

Environmental Science and Engineering

Advisor(s)

Jorge L. Gardea-Torresdey

Abstract

Nanotechnology has a great potential in ensuring food production, security and safety globally. Over the past decade, research on the use of nanomaterials to supply nutrient elements and protect plants from pest and diseases has significantly increased. Tomato (Solanum lycopersicum) is one of the most consumed vegetables in the world and United State is one of its largest producers globally generating billions of dollars annually in revenue.. Tomato plants are affected worldwide by Fusarium wilt caused by Fusarium oxysporum f. sp. Lycopersici. There is growing concern about excessive use of conventional pesticides in controlling Fusarium and other diseases in tomato production. Nanoparticles have been reported to potentially increase plant growth and yield, and improve the nutritional value by enhancement of essential micronutrient required by the plants. However, little is known about the impact of nanoparticle elements on disease suppression, in tomato. This research was aimed at evaluating the potential of nanoscale elements in suppression of Fusarium wilt disease in tomato, enhance macronutrient use efficiency, and increase its yield.

The research was developed in two phases. In the first phase, three week-old Bonny Best cultivar seedlings were exposed, by root or foliar pathways, to CeO2 nanoparticles and cerium acetate at 50 and 250 mg/L prior to transplant into sterilized soil. One week later, the soil was inoculated with the fungal pathogen F.oxysporum f. sp. lycopersici (1 g/kg) and plants were cultivated to maturity in a greenhouse.. Disease severity was significantly reduced by 250 mg/L of nano-CeO2 and CeAc applied to the soil (53% and 35%, respectively) or foliage (57% and 41%, respectively), compared with non-treated infested controls. In addition, Fusarium infection decreased fruit height (10%), dry weight (42%) and lycopene (17%), and increased the total sugar (60%) and Ca content (140%) in infested untreated control, compared with the non-infested untreated control (p ≤ 0.05). Foliar exposure to NP CeO2 at 250 increased the fruit dry weight (67%) and lycopene content (9%) in infested plant, compared with the infested untreated control. Foliar exposure to CeAc at 50 mg/L reduced fruit fresh weight (46%), and water content (46%), and at 250 mg/L increased fruit dry weight (94%), compared with infested untreated control. Fruit lycopene content also increased by 11% in infested plants exposed to CeAc at 50 mg/kg via root, compared with untreated infested control. Total sugar contents decreased in fruits of infested plants exposed via roots to NP CeO2 at 50 mg/kg (63%), at 250 mg/kg (54%), CeAc at 50 mg/kg (46%), and foliarly at 50 mg/L (50%) and 250 mg/L (50%), compared with infested untreated control. Overall, the findings show that nano-CeO2 has potential to suppress Fusarium wilt, improve the chlorophyll content in tomato plants and has negligible effects on the nutritional value of tomato fruit.

In the second phase, we investigated the physiological and biochemical effect of copper oxide nanoparticles on tomato plant grown in F. oxysporum infested soil. Bonny Best tomato seedlings (three weeks old) were exposed to copper oxide nanoparticles (nCuO at 250 or 500 mg/L, root and foliar), CuSO4 (25 or 50 mg/L, foliar) and commercial fungicide, Kocide 3000, and transplanted into pots containing 1 kg sterilized soil mixture (1 natural: 2 potting mix). Seven days after the transplant, a group was inoculated with Fusarium (1 g/kg soil ~100,000 colonies) and cultivated in a greenhouse until the flowering stage (5 weeks after transplant). The root and shoot physiological parameters, biomass, plant height, chlorophyll content, enzyme activities (polyphenol oxidases and catalase), total proteins, micro, and macro elements were evaluated. Chlorophyll content reduced by 11% in infested control, relative non-infested control but increased in plants exposed to CuSO4 at 25 mg/L (8%) and 50 mg/L (9%), compared with infested untreated control (p ≤ 0.05). Chlorophyll content was elevated in plants treated foliarly with nCuO at 250 (10%), 500 (14%), and CuSO4 (15%), and via root to nCuO at 500 mg/kg (14%), compared with plant treated with Kocide 3000. Root exposure to nCuO at 500 mg/kg increased Shoot fresh weight by 18%. Root fresh weight increased in plant exposed to foliar treatment with nCuO at 250 mg/L (36%), and root exposure at 250 and 500 mg/kg by 33%, compared with untreated infested control. Root polyphenol oxidase and catalase activities increased plant exposed via root to nCuO at 500 mg/L (178%), and foliarly with CuO at 250 mg/L (138%), respectively, compared with untreated infested control. Overall, nCuO improved the chlorophyll content, increased plant biomass, and improve defense mechanism against the pathogen.

This study revealed that the tested nanoparticles (CeO2 and CuO) has the ability to suppress Fusarium wilt disease in tomato, improve its chlorophyll content, and increase its yield and alter the nutritional content, and rely on antioxidant and microbial properties of Ce and Cu. These findings opens an opportunity for utilization of these nanoparticle as fungicides. Therefore, formulations containing nanoparticle micronutrients may proffer a new strategy that can suppress plant diseases and increase the yield. However, more research work needs to be done to fully understand the mechanism behind the nanoparticle-pathogen interaction in plants.

Language

en

Provenance

Received from ProQuest

File Size

143 pages

File Format

application/pdf

Rights Holder

Ishaq Olarewaju Adisa

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