Fungal spores exhibit TWO TYPES of dormancy, described as CONSTITUTIVE
(endogenous) and EXOGENOUS.
- Constitutive dormancy:
- Commonly exhibited by SEXUAL FUNGAL
- 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
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
- 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
- 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