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Fusarium oxysporum as an Opportunistic Fungal Pathogen on Zinnia hybrida Plants Grown on board the International Space Station.

Authors
  • Schuerger, Andrew C1
  • Amaradasa, Bimal S2
  • Dufault, Nicholas S2
  • Hummerick, Mary E3
  • Richards, Jeffrey T3
  • Khodadad, Christina L3
  • Smith, Trent M4
  • Massa, Gioia D4
  • 1 Department of Plant Pathology, University of Florida, Exploration Park, Merritt Island, Florida, USA.
  • 2 Department of Plant Pathology, University of Florida, Gainesville, Florida, USA.
  • 3 AECOM Management Services, Kennedy Space Center, Florida, USA.
  • 4 NASA Exploration Research and Technology Programs, Kennedy Space Center, Florida, USA.
Type
Published Article
Journal
Astrobiology
Publisher
Mary Ann Liebert
Publication Date
Sep 01, 2021
Volume
21
Issue
9
Pages
1029–1048
Identifiers
DOI: 10.1089/ast.2020.2399
PMID: 33926205
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

A plant production system called Veggie was launched to the International Space Station (ISS) in 2014. In late 2015, during the growth of Zinnia hybrida cv. 'Profusion' in the Veggie hardware, plants developed chlorosis, leaf curling, fungal growth that damaged leaves and stems, and eventually necrosis. The development of symptoms was correlated to reduced air flow leading to a significant buildup of water enveloping the leaves and stems in microgravity. Symptomatic tissues were returned to Earth on 18 May 2016 and were immediately processed to determine the primary causal agent of the disease. The presumptive pathogen was identified as Fusarium oxysporum by morphological features of microconidia and conidiophores on symptomatic tissues; that is, by epifluorescent microscopy (EFM), scanning electron microscopy (SEM), metabolic microarrays, and ITS sequencing. Both EFM and SEM imaging of infected tissues showed that germinating conidia were capable of stomatal penetration and thus acted as the primary method for infecting host tissues. A series of ground-based pathogenicity assays were conducted with healthy Z. hybrida plants that were exposed to reduced-airflow and high-water stress (i.e., encased in sealed bags) or were kept in an unstressed configuration. Koch's postulates were successfully completed with Z. hybrida plants in the lab, but symptoms only matched ISS-flown symptomatic tissues when the plants were stressed with high-water exposure. Unstressed plants grown under similar lab conditions failed to develop the symptoms observed with plants on board the ISS. The overall results of the pathogenicity tests imply that F. oxysporum acted as an opportunistic pathogen on severely high-water stressed plants. The source of the opportunistic pathogen is not known, but virulent strains of F. oxysporum were not recovered from unused materials in the Veggie plant pillow growth units assayed after the flight.

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