The fungal group Mycelia sterilia
– its interactions with crop plants and their pathogens
 

Olga Vinnere, Jamshid Fatehi and Berndt Gerhardson

Plant Pathology and Biocontrol Unit, SLU

P.O. Box 7035, Uppsala, Sweden

What others say

What are Mycelia sterilia?

Mycelia sterilia is a large group of fungi that share the property of being defective in forming true spores and consists of fungi of various morphological types (Hawksworth et al., 1983). The classical fungal systematics, which is mainly based on the comparison of the morphology of spores, conidiogenous cells and fruiting bodies, therefore cannot be applied for the classification of these organisms. Spore formation has been induced in laboratory under very specific conditions in some members of this group. The discovery of distinct but rare sexual forms in some members of M. sterilia has revealed that the group is not homogenous and they are, indeed, belonging to different, distantly related classes of fungi.

The advent of molecular techniques such as sequencing of the ribosomal genes and their spacers could be a potential approach for the classification of M. sterilia and identification of the isolates of this group.

What do Mycelia sterilia do and how?

These fungi are ubiquitous. Some members of M. sterilia, such as Rhizoctonia and Sclerotium, are important plant pathogens worldwide. On the other hand, some isolates of sterile fungi associated with roots have been reported as efficient plant growth promoters on many crops (Jacobs, 1994; Barrow, 1995). Several isolates of sterile mycelia have also been found to act as biocontrol agents against pathogenic fungi such as Gaeumannomyces graminis, Pythium ultimum, etc. (Dewan and Sivasithamparam, 1989; Martin et al., 1984). In such cases the mechanisms involved in biocontrol may include: i) ability to compete with pathogens for space; ii) ability to compete for nutrients; iii) antifungal activity through the metabolite production; iv) ability to promote plant growth by supplying the host plant with nutrients and/or plant growth-promoting compounds.

 What we are doing:

* Isolations from roots of agricultural crops and wild herbaceous plants in Sweden and Latvia:

  • 1 min 1% NaOCl surface sterilisation
  • weak medium (Water Agar)
  • lactic acid and streptomycin added
    •

* Selection of sterile isolates and subsequent attempts to induce sporulation:

  • Near UV light (l =380-420 nm)
  • different media (Malt Extract Agar, Minimal Medium, Potato Carrot Agar, Oatmeal Agar, 1/5 Potato Dextrose Agar)
  • addition of plant tissue (lupine stems)
  • combination of all above

* Greenhouse experiments:

* Plants of four different genera (tomato, rape, wheat and peas)

* Metabolite profile (in collaboration with AgriVir AB)

* DNA and Pectic Zymogram analyses

Our results after one year:

* Large collection of fungal isolates obtained

* Among them there are many slowly sporulating fungi, but very few "truly sterile" strains;

* Many slowly sporulating, non-pathogenic isolates belong to Phoma spp.;

* Several isolates are plant growth promoting, there are also plant pathogenic ones;

* There is a sort of host plant specificity (?);

* Metabolites of several isolates have a sort of antifungal activity.