Embed Size (px)
Citation preview
1
Myriam de Haan1 and Marc Lemmens2
Exploring myxomycetes for possible applications as antagonists in bio-control of plant pathogens
1) Meise Botanic Garden, Belgium 2) University of Natural Resources and Life Sciences, Vienna, Austria
Myriam de Haan & Marc Lemmens
Content 2
Towards bio-control using Myxomycetes
Content
• Introduction to plant pathogens and bio-control • Introduction to Myxomycetes • Myxomycetes as possible antagonists • Conclusions
Myriam de Haan & Marc Lemmens
Introduction 3
Plant pathogens
Infection of maize ears by Fusarium graminearum
An example of plant disease is illustrated here: maize ear rot
Maize ears can be colonised for example with the fungus Fusarium graminearum.
The ear is infected by macroconidia, and the fungus produces mycotoxins which are toxic for humans and animals.
Myriam de Haan & Marc Lemmens
10 µm
4
Type Mechanism Remarks
Direct antagonism
- Predation
E.g. Trichoderma
Mixed-path antagonism
- Antibiotics
E.g. cyclic lipopeptides
- Lytic enzymes
Chitinases, cellulases, proteases
Indirect antagonism
- Competition
“First-come first-serve principle”
- Induction of host resistance
Activation of the natural plant defence reactions
Types of antagonism against plant pathogens
Introduction Myriam de Haan & Marc Lemmens
0,5 mm 10 µm
0,5 cm
100 µm
10 µm
Stalked sporocarp
Spore
Germination
Myxamoebae
Myxoflagellates
Fusion
Zygote
Plasmodium
Haploid Diploid
Life cycle of a myxomycete
Myriam de Haan & Marc Lemmens
Conidia of Alternaria sp.
Myxomycetes as possible antagonists 6
“Waste” deposited in the hypothallus
Macroconidia of Fusarium spp.
Didymium squamulosum
Myriam de Haan & Marc Lemmens
20 µm 20 µm
20 µm 1 mm
Phagocytosis of Fusarium macroconidia
A Didymium sp. takes up macroconidia via phagocytosis and distributes it in the cytoplasm
7 Myxomycetes as possible antagonists Myriam de Haan & Marc Lemmens
Conidia from Alternaria floating in the moving cytoplasmic stream in the plasmodium of a slime mould
0,5 cm
50 µm
8
Slime moulds feeding on mycelium of Fusarium day 0
2 weeks
1 week
Myriam de Haan & Marc Lemmens Myxomycetes as possible antagonists
9
Fungicidal activity in the glycocalyx?
Myxomycetes can ingest fungal spores (e.g. Alternaria sp.) via phagocytosis red arrow Non-digested parts are deposited in the slime sheath (exocytosis) green arrow Spores look intact but are not germinating Germination of fresh Fusarium macroconidia deposited on the slime sheath was
retarded => fungicide activity?
Myriam de Haan & Marc Lemmens Myxomycetes as possible antagonists
50 µm
1 cm
10
Herrera NA, Rojas C, Franco-Molano AE, Stephenson SL, Echeverri F. (2011) Physarella oblonga centered bioassays for testing the biological activity of myxomycetes.
Mycosphere 2 (6), 637–644, Doi 10.5943/mycosphere/2/6/4
Antifungal activity in Myxomycetes
Myriam de Haan & Marc Lemmens Myxomycetes as possible antagonists
11
Slime moulds feed on pollen and anthers Pollen and anthers are used as feed by the Fusarium and strongly promote plant infection
start
16 hours
Myxomycetes can feed on pollen and anthers from wheat and maize
Myriam de Haan & Marc Lemmens Myxomycetes as possible antagonists
50 µm
20 µm
12
Type Mechanism Remarks Direct antagonism
- Predation Against Fusarium/Alternaria/Yellow rust => uptake of spores Phagocytosis of plant pathogenic bacteria
Mixed-path antagonism
- Antibiotics
Fungicides/bactericides. In the glycocalyx?
- Lytic enzymes Extracellular: digestion of mycelium
Indirect antagonism
- Competition
Consumption of pollen and anthers (feed for Fusarium)
- Induction of host resistance
?
Possible types and mechanisms of antagonism of myxomycetes
The presence and combination of several mechanisms of antagonism make Myxomycetes interesting candidates for a possible practical application as antagonists used in bio-control of plant pathogenic fungi and bacteria
Myriam de Haan & Marc Lemmens Myxomycetes as possible antagonists
13
1) Collecting Myxomycetes: mainly soil-born species isolated from maize
2) Identification of the species and long-term storage
3) Myxo-farming (production of bio-mass): - spores - induction of microcysts - induction of sclerotia (macrocysts) - induction of sporulation
4) In vitro tests, greenhouse and field tests
Towards bio-control with slime moulds:
Basic strategy
Myriam de Haan & Marc Lemmens Myxomycetes as possible antagonists
14
Collecting myxomycetes from maize
• Mist irrigation system is used to promote Fusarium diseases on
the maize ear => also promotes slime mould development
• Over 500 specimens from maize were collected in 2015-2017
• On maize mainly Didymium and Physarum spp.
• Isolated slime moulds species on maize plants are soil born
• Therefore they must be able to survive in the soil and compete with the soil micro-organisms
Myriam de Haan & Marc Lemmens Myxomycetes as possible antagonists
10 µm
Spore
Germination
Myxamoebae
Myxoflagellates
Myxomycetes as possible antagonists
Important for practical applications: SHELVE LIFE
Two durable structures: • Spores and Microcysts
- survive 2 years
15
10 µm
20 µm
Myriam de Haan & Marc Lemmens Myxomycetes as possible antagonists
Stalked sporocarp
Microcysts
0,5 mm
0,5 cm
Stalked sporocarp
Plasmodium
Important for practical applications: SHELVE LIFE
Durable structure • Sclerotium:
- Consists of macrocysts - survive 2 years - fast germination - coalesce to a large plasmodium
16
Sclerotium 0,25 cm
Myxomycetes as possible antagonists
Myriam de Haan & Marc Lemmens Myxomycetes as possible antagonists
17
• Possible application: protect seeds of agricultural crops against invasion of soil-born pathogens during germination
• Seed treatment or seed dressing is a chemical treatment, typically with a fungicide, with which seeds are treated (or "dressed") prior to planting
• Use of macrocysts/spores for seed dressing: - possible alternative solution to classical dressing methods - after germination in the presence of water a plasmodium will develop - control of soil-born plant-pathogenic bacteria and fungi?
Example of a bio-control application
? ©
External coat Food (beneficial bacteria) Fibroid layer (to allow movement of the plasmodium around the seed) Layer with macrocysts or spores
Seed
Myriam de Haan & Marc Lemmens Myxomycetes as possible antagonists
Conclusion 18
Conclusion
Publications on the use of slime moulds as antagonists?
Zero!! (at the best of our knowledge)
Why?
• “What the heck are Myxomycetes?” Slime moulds are not well known
• Usually not commercially available (in contrast to bacteria, yeasts and fungi)
• Taxonomy: - experienced taxonomists are rare - research for molecular identification is still in the early stages
• Myxo-farming for production of bio-mass, few studies even less results
Myriam de Haan & Marc Lemmens
Acknowledgement 19
Acknowledgement
Hoda Jabbarimalayeri Johann Gangl Imer Maloku
Thank you for your attention
Myriam de Haan & Marc Lemmens
