Date of Award

12-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Plant and Environmental Science

Advisor

Agudelo, Paula

Committee Member

Tharayil, Nishanth

Committee Member

Gerard, Patrick

Committee Member

Benson, Eric

Abstract

Plant-parasitic nematodes cause significant losses to plant agriculture annually. The limited availability and high cost of synthetic nematicides, along with the environmental risks associated with their use, have created a renewed interest in the search for alternative management tactics. One such alternative tactic is the use of plant extracts. The focus of this research is the evaluation of the nematicidal activity of water extracts from Pokeweed (Phytolacca americana). In vitro and greenhouse tests were performed to evaluate the effects of the extracts on five species of plant-pathogenic nematodes of economic importance: Aphelenchoides fragariae, Ditylenchus dispsaci, Meloidogyne incognita, Pratylenchus penetrans, and Rotylenchulus reniformis. Chapter 1 describes an in vitro method for screening of compounds in aqueous suspensions, using small volumes. The results show differential susceptibility of three species of nematodes to oxamyl, the carbamate nematicide used as positive control. The mode of action of oxamyl is through the inhibition of acetylcholinesterase (AChE). The marked differences in the inhibition potency of oxamyl on AChE of D. dipsaci, P. penetrans and A. fragariae are discussed. Chapter 2 reports the results of screening for nematicidal activity of extracts from six plants: Aloe barbadensis (aloe), Ilex opaca (American holly), Nerium oleander (oleander), Phytolacca Americana (pokeweed), Pueraria montana (kudzu), and Quercus shumardii (red oak). Different plant parts and two extraction methods were evaluated for each plant species on three nematode species. Results showed that extracts from pokeweed leaves were the only ones with consistently high activity against the three nematode species. Additionally, different solvents were evaluated for extraction of compounds from pokeweed leaves, including acetone, ethanol, and methanol. Chapter 3 evaluates water extracts from pokeweed leaves in the greenhouse for activity against R. reniformis and M. incognita on soybean plants. Greenhouse results show the extracts are a promising alternative for management of M. incognita. Extracts were analyzed by chromatography for identification of prominent compounds with reported activity against other microorganisms. Two of the compounds identified, astragalin and chlorogenic acid, were evaluated in vitro individually, but did not show nematicidal activity at the concentrations present in the extracts. Based on in vitro and greenhouse assays, we conclude that pokeweed leaf extracts show nematicidal activity that could be incorporated in an integrated pest management plan for several plant-pathogenic nematode species.

Share

COinS