Doctoral Dissertations

Date of Award

12-2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Entomology, Plant Pathology and Nematology

Major Professor

Bonnie Ownley

Committee Members

Gwinn Kimberly D, Bernard Ernest C, Butler David M, Parwinder Grewal

Abstract

Beneficial microbial endophytes live inside plants and establish a mutualistic relationship with the host plant, obtaining nutrition and shelter, and providing protection to the host against biotic and abiotic stresses. Beneficial endophytes have emerged as alternatives to chemical pesticides for control of plant pests and diseases. The insect pathogenic fungus, Beauveria bassiana (Bb), is endophytic in some plant species. Remarkably, endophytic Bb can protect host plants against both insect pests and plant pathogens. However, less is known about the effectiveness of Bb against phytopathogens, especially plant-parasitic nematodes. Therefore, to better understand the body of published research on endophytic Bb, three separate meta-analyses were performed to determine: 1) the rate of colonization of various plant species by endophytic Bb; 2) the efficacy of endophytic Bb against insect pests, and 3) the suppression of plant pathogens by endophytic Bb. Furthermore, efficacy of Bb against root knot nematodes was tested with an in vitro bioassay. Meta-analysis revealed that Bb most effectively colonizes eudicots, angiosperms, the family Brassicaceae, and the edible crop, faba bean. Colonization was most effective in leaves and plants with fibrous roots, and when Bb was applied to foliage of whole plants. Meta-analysis of endophytic Bb efficacy against insects revealed that Bb was most effective against the insect order Hemiptera, family Aphididae, especially cotton aphids. Meta-analysis on phytopathogens indicated that endophytic Bb could significantly suppress plant disease, especially aphid-borne potyvirus. In nematode assays, Bb inhibited Meloidogyne incognita egg hatch, and hatch was indirectly proportional to the ratio of Bb conidia to nematode eggs. In summary, endophytic Bb has activity against insect pests and plant pathogens, including plant-parasitic nematodes. Meta-analyses provided a comprehensive view of the current knowledge on endophytic Bb research. These findings provide a valuable tool in further development of Bb as a sustainable plant disease management strategy.

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