The converse of heteroecious, which means that a rust or an aphid is obliged to change its species of host in order to complete its life cycle. An autoecious rust is one that completes its entire life cycle on one species of host. However, entomologists use the term 'monoecious' in place of autoecious when describing aphids. Unfortunately, in botany, monoecious means that separate male or female flowers occur on a single plant (See also dioecious, hermaphodite). Autogamy

(Greek: auto = self; gamy = marriage). Self-fertilisation, or self-pollination. An autogamous species is one in which individual flowers, or plants, are fertilised with their own pollen. However, some cross-pollination always occurs in an autogamous species and variability is always maintained. (See also: allogamy). Auto-infection

Infection is the contact made by one parasite individual with one host individual for the purposes of parasitism. Autoinfection (Greek: auto = self) means that the parasite was born on (or in) the host that it infects; it had no need to travel to its host. Auto-infection is possible only after a matching allo-infection has occurred. The parasite then reproduces asexually to produce a clone in which all individuals are identical. It follows that, in terms of the gene-for-gene relationship, all autoinfection is matching infection. Consequently, vertical resistance cannot control auto-infection, which can be controlled only by horizontal resistance. Because all parasitism involves auto-infection, it must be concluded that horizontal resistance occurs in every host, against every parasite of that host. (See also: allo-infection, autogamy). Autoployploid

A polyploid has more than two sets of chromosomes (e.g., triploid, tetraploid). In an autopolyploid, all the chromosomes are derived from the same species. In an allopolyploid, the chromosomes are derived from two or more different species. Auxin

Auxins are plant hormones. Avena fatua

Wild oats. This species can be a serious weed as it is difficult to control in cereal crops. Avena sativa

Cultivated oats. This species is a hexaploid and the first controlled crosses were made by a Scottish farmer, one Patrick Sheriff, in 1860. Subsequently, most professional work has used pedigree breeding and back-crossing with a view to introducing vertical resistances. However amateur breeding for horizontal resistance is entirely feasible and a male gametocide, as used with wheat, will probably be effective.

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