Exploring myxomycetes for possible applications as antagonists in bio-control of plant pathogens

Transcription

1 Exploring myxomycetes for possible applications as antagonists in bio-control of plant pathogens Myriam de Haan 1 and Marc Lemmens 2 1) Meise Botanic Garden, Belgium 2) University of Natural Resources and Life Sciences, Vienna, Austria 1

2 Towards bio-control using Myxomycetes Content Introduction to plant pathogens and bio-control Introduction to Myxomycetes Conclusions Content 2

3 Plant pathogens 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. 10 µm Infection of maize ears by Fusarium graminearum Introduction 3

4 Types of antagonism against plant pathogens Type Mechanism Remarks Direct antagonism - Predation E.g. Trichoderma Mixed-path antagonism Indirect antagonism - Antibiotics E.g. cyclic lipopeptides - Lytic enzymes Chitinases, cellulases, proteases - Competition First-come first-serve principle - Induction of host resistance Activation of the natural plant defence reactions Introduction 4

5 Life cycle of a myxomycete Spore Myxamoebae 0,5 mm Germination 10 µm Stalked sporocarp Myxoflagellates Diploid Haploid 0,5 cm Fusion Zygote 100 µm Plasmodium 10 µm

6 Waste deposited in the hypothallus 1 mm Didymium squamulosum 20 µm Macroconidia of Fusarium spp. 20 µm 20 µm Conidia of Alternaria sp. 6

7 Phagocytosis of Fusarium macroconidia 0,5 cm 50 µm Conidia from Alternaria floating in the moving cytoplasmic stream in the plasmodium of a slime mould A Didymium sp. takes up macroconidia via phagocytosis and distributes it in the cytoplasm 7

8 Slime moulds feeding on mycelium of Fusarium day 0 1 week 2 weeks 8

9 Fungicidal activity in the glycocalyx? 1 cm 50 µm 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? 9

10 Antifungal activity in Myxomycetes 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), , Doi /mycosphere/2/6/4 10

11 Slime moulds feed on pollen and anthers Pollen and anthers are used as feed by the Fusarium and strongly promote plant infection start Myxomycetes can feed on pollen and anthers from wheat and maize 16 hours 50 µm 20 µm 11

12 Possible types and mechanisms of antagonism of myxomycetes Type Mechanism Remarks Direct antagonism - Predation Against Fusarium/Alternaria/Yellow rust => uptake of spores Phagocytosis of plant pathogenic bacteria Mixed-path antagonism Indirect antagonism - Antibiotics Fungicides/bactericides. In the glycocalyx? - Lytic enzymes Extracellular: digestion of mycelium - Competition Consumption of pollen and anthers (feed for Fusarium) - Induction of host resistance? 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 12

13 Towards bio-control with slime moulds: Basic strategy 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 13

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 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 14

15 Important for practical applications: SHELVE LIFE Spore 10 µm Two durable structures: Spores and Microcysts - survive 2 years Microcysts Stalked sporocarp Germination Myxamoebae 20 µm Myxoflagellates 10 µm 15

16 Important for practical applications: SHELVE LIFE 0,5 mm Durable structure Stalked sporocarp Sclerotium: - Consists of macrocysts - survive 2 years - fast germination 0,5 cm - coalesce to a large plasmodium Plasmodium Sclerotium 0,25 cm 16

17 Example of a bio-control application 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? External coat Food (beneficial bacteria) Fibroid layer (to allow movement of the plasmodium around the seed) Layer with macrocysts or spores Seed 17

18 Conclusion Publications on the use of slime moulds as antagonists? Why? Zero!! (at the best of our knowledge) 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 Conclusion 18

19 Acknowledgement Hoda Jabbarimalayeri Johann Gangl Imer Maloku Thank you for your attention Acknowledgement 19