Alternating Pathosystem Discontinuity

An alternating pathosystem can have sequential discontinuity that may be real, functional, or 'alternational'. These terms must now be defined.

The real discontinuity occurs with a genuinely discontinuous host population such as an annual herb, or the leaves of a deciduous tree. During the winter, there is no host tissue available to the parasite. This is the typical situation with the summer host of an alternating parasite.

The functional discontinuity occurs with special mechanisms that change an apparently continuous pathosystem into a discontinuous pathosystem (see 8.11).

The alternational discontinuity results from the alternating parasite being obliged to change its host. Thus, spring alternators cannot auto-infect the winter host, and this parasitism ceases during the summer. The winter host can only be allo-infected in the autumn, and it is parasitised during the winter.

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