A parasite of a parasite. One of the principle agents of biological control. For example, rust is a parasite of coffee leaves, and it has a hyper-parasitic grub that eats its spores. There is also a hyper-hyper-parasite, a wasp that parasitises this grub. If coffee trees are sprayed with insecticides, the effects of this hyper-parasitism are lost. See also: Predator. Hypersensitive fleck

A small necrotic speck, just visible to the naked eye, which indicates a hypersensitive reaction of a gene-for-gene relationship to a non-matching allo-infection. Hypersensitivity

The process in which a group of cells surrounding an infection site dies very rapidly, and the infecting parasite dies with them. The infection then fails. This is a common mechanism of vertical resistance against allo-infections in leaves, but note that not all vertical resistance is due to hypersensitivity (e.g., Fusarium and Verticillium wilts), and not all hypersensitivity is due to vertical resistance. See also: Hypersensitive fleck. Hypha

A single strand of microscopic fungal mycelium.

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