Spore Dormancy

Fungal spores exhibit TWO TYPES of dormancy, described as CONSTITUTIVE (endogenous) and EXOGENOUS.

Constitutive dormancy:
  • Commonly exhibited by SEXUAL FUNGAL SPORES.
  • Is imposed by some INHERENT (ENDOGENOUS) CHARACTERISTIC of the spore itself which prevents it from germinating.
  • Spores may fail to germinate even when environmental conditions appear favourable for growth.
  • Some may require a period of ageing or a specific activation trigger, such as heat-shock or cold-shock.
  • E.g. uredospores of Puccinia graminis, cause of rust disease in cereal crops:
    • Ensure they don't germinate while in close proximity to one another and consequently compete for a limited supply of nutrients in the environment.
    • Because they contain METHYL-CIS-FERULATE, a water-soluble and volatile inhibitor of germination.
    • Germinate once thoroughly dispersed from one another and methyl-cis-ferulate has leached out of the spore and become diluted in the environment.
Exogenous dormancy:
  • Commonly exhibited by ASEXUAL FUNGAL SPORES.
  • Imposed by an UNFAVOURABLE ENVIRONMENT (i.e. exogenous factors).
  • Factors influencing dormancy include availability of moisture and nutrients, as well as temperature and pH.
  • Spores germinate only if and when environmental conditions are favourable for growth.
  • E.g. conidia of Aspergillus species.
Fungistasis (mycostasis):
  • A phenomenon LINKED TO EXOGENOUS DORMANCY.
  • It is the inhibition of fungal growth without any effect on viability of the fungus.
  • Spores may fail to germinate in natural environments (e.g. soil or leaf surfaces) because of the activities of other micro-organisms.
  • This inhibition may be due to INHIBITORY METABOLITES produced by other micro-organisms and/or COMPETITION for a limited amounts of nutrients available.
  • The EFFECT IS REVERSIBLE - once the inhibitory substances are removed (or become diluted) or additional nutrients become available the spores will germinate (or the mycelium will resume growth).

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