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.
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