There are
at least five reasons why fungi may cause catastrophic plant disease.
(1) They
sporulate prolifically, the spores providing copious inoculum which may infect
further plants.
(2) Their
latent period, i.e. the time between infection and the production of further
infectious propagules, usually spores, may be only a few days.
(3) The
spores, if they are wettable, may be spread as high-density inoculum in surface
water or in droplets by rain-splash. Alternatively, non-wettable spores may be
carried long distances by the wind.
(4) They
may produce compounds that are phytotoxic and/or a battery of enzymes that
destroy the plant’s structure.
(5)
Biotrophic pathogens, such as the rusts and mildews, draw nutrients away from
the economically valuable part of the plant by the production or induction of
growth regulators such as cytokinins and consequently depress yields.
