Entomology, Department of
First Advisor
Joe Louis
Second Advisor
Kyle Koch
Third Advisor
Paul Ayayee
Date of this Version
5-2024
Citation
A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science
Major: Entomology
Under the supervision of Professor Joe Louis
Lincoln, Nebraska, May 2024
Abstract
Sorghum (Sorghum bicolor) is a vital cereal crop globally, facing challenges from invasive pests such as the sugarcane aphid (SCA; Melanaphis sacchari). To elucidate mechanisms of sorghum resistance to SCA, we examined the role of plant defenses and the influence of aphid-associated microbes in modulating sorghum defenses. Lignin is a complex heterogenous polymer present in nearly all plant cell walls that plays a critical role in protecting plants from various stresses. In this study, we investigated the role of the caffeoyl coenzyme-A O-methyltransferase (CCoAOMT), one of the core enzymes in monolignol biosynthesis pathway that leads to lignin formation, in sorghum defense against SCA. Gene expression studies demonstrated upregulation of SbCCoAOMT upon SCA infestation, leading to reduced aphid reproduction and settling. Electrical penetration graph (EPG) analyses showed restricted aphid feeding from sieve elements in SbCCoAOMT-overexpressing plants. While lignin accumulation was observed in response to SCA feeding, feeding bioassays with phenolic compounds indicated direct adverse effects on SCA reproduction. Our results suggest that SbCCoAOMT overexpression-mediated enhanced accumulation of phenolic acids may have negatively impacted SCA growth and reproduction. Additionally, using SCA-resistant (SC265) and susceptible (SC1345) sorghum lines, we investigated variations in SCA gut microbiomes during feeding and the role of aphid-associated microbes in modulating sorghum defenses. Our analysis revealed that the SCA fed on susceptible and resistant sorghum lines had Pseudomonadaceae and Rhizobiaceae, respectively, as the most abundant bacterial families. Our integrated approach highlights the potential of modulating plant defenses and aphid-associated microbes to bolster sorghum resistance to SCA and offers insights into developing aphid-resistant sorghum varieties.
Advisor: Joe Louis
Comments
Copyright 2024, Edith Ikuze. Used by permission