In Vitro Assay Development to Screen Early and Late Leaf Spot Pathogens for SDHI, DMI, and QoI Resistance Management
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Authors
Effi, Gideon
Issue Date
2026-01-20
Type
Thesis
Language
en_US
Keywords
Plant diseases , Fungicide resistance , Fertilization in vitro , Nothopassalora personata , Passalora arachidicola , Peanuts--Diseases and pests , Academic theses
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Abstract
ABSTRACTFungicide resistance in plant pathogens poses a significant threat to global food security. Early leaf spot, caused by Passalora arachidicola, and late leaf spot, caused by Nothopassalora personata, are major diseases of peanuts (Arachis hypogaea). In vitro studies of these slow growing pathogens have been limited. This study optimized two assays: a microtiter plate assay for measuring biomass in liquid medium and a resazurin assay for detecting fungal metabolism, with a focus on incubation periods and inoculum concentrations. We performed a fungicide resistance study comparing germination assays, biomass inhibition assays on solid media, and optimized assays. Isolates were exposed to various concentrations of SDHI, QoI, and DMI, and the effects of different inoculum types (conidia and homogenate) on biomass inhibition assays were examined. Our optimization study revealed that for the microtiter plate assay, the ideal incubation periods were 6 days for P. arachidicola and 8 days for N. personata. In the resazurin assay, optimal incubation was 2 days for P. arachidicola and 3 days for N. personata. In the assay comparison study, the assays generally did not differ in their ability to detect sensitivity to effective fungicides (P ≥ 0.59), except for N. personata with pydiflumetofen (P = 0.033). Significant differences were found between assays for ineffective fungicides (P ≤ 0.006), except for P. arachidicola with azoxystrobin (P = 0.239). Four out of six cases for effective fungicides showed that the inoculum did not affect results, while three out of five instances indicated it did matter for ineffective fungicides. Consequently, the choice of in vitro assay and inoculum can impact conclusions. The resazurin assay is more sensitive in detecting resistance than the other assays, while the homogenate shows more resistance than the conidia.
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This dissertation is protected by the Copyright Laws of the United States (Public Law 94-553, revised in 1976). Consistent with fair use as defined in the Copyright Laws, brief quotations from this material are allowed with proper acknowledgement. Use of the materials for financial gain with the author's expressed written permissions is not allowed.