Degree Type

Thesis

Date of Award

2019

Degree Name

Master of Science

Department

Plant Pathology and Microbiology

Major

Plant Pathology

First Advisor

Gary P. Munkvold

Abstract

Fungal colonization and mycotoxin contamination are chronic problems that can compromise grain quality and safety in stored maize. Aflatoxins, associated with Aspergillus flavus Link infection, are the most economically important mycotoxins. Insect damage is a major factor that predisposes grain to infection by mycotoxigenic fungi. Indianmeal moth (Plodia interpunctella Hübner) and maize weevil (Sitophilus zeamais Motschulsky) are lepidopteran and coleopteran stored-grain insects, respectively, that can cause considerable damage in stored maize. The effect of Indianmeal moth or maize weevil infestations on A. flavus colonization and vice versa in non-Bt and Bt maize hybrids with lepidopteran and coleopteran events were evaluated in this study. After 28 days of storage at 32°C and 80-85% relative humidity, the presence of Indianmeal moth or maize weevil did not enhance A. flavus colonization in non-Bt or Bt hybrids. No Indianmeal moths or maize weevils survived in grain of Bt hybrids with lepidopteran or coleopteran resistance genes, respectively. Aflatoxin levels in the 106 A. flavus inoculated non-Bt grain increased significantly in the presence of Indianmeal moth or maize weevil (p ≤ 0.01), but aflatoxins in the Bt hybrids were unaffected by insect infestation. A. flavus caused increased mortality, reduced survivorship, and lower growth indices of both insects, hence, limiting their feeding activity in the inoculated grain compared to the uninoculated. As a result, damage (p ≤ 0.0001) and grain weight loss (p ≤ 0.01) were significantly higher in the uninoculated non-Bt hybrid. In the transgenic hybrids, no damage and grain weight loss were observed regardless of the presence or absence of A. flavus, due to 100% mortality of insects. A. flavus effects on insects were evident only in non-Bt hybrid and insect infestation only enhanced aflatoxin contamination in the absence of Bt protection. Mycotoxin reduction in Bt maize has been well-studied in the field but not in storage. This study demonstrated that Bt protection was effective against stored-grain insects Indianmeal moth and maize weevil. The use of Bt hybrids can mitigate the risk of A. flavus infection and aflatoxin contamination related to stored-grain insects.

Copyright Owner

Julie Aiza L. Mandap

Language

en

File Format

application/pdf

File Size

99 pages

Available for download on Wednesday, November 25, 2020

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