The microscopic spores produced by sexual fusion in many parasitic fungi belonging to the Peronosporles (downy mildews). Most oospores are very hardy, and are formed at the end of a discontinuous epidemic. They are resistant to desiccation and cold, and they enable the fungus to survive an adverse season, such as a tropical dry season, or a temperate winter, when no host tissue is available to the parasite. Being the result of sexual recombination, they also produce a wide diversity of vertical pathotypes at the beginning of the epidemic, when there is a wide diversity of vertical pathodemes to be matched. Oospores should not be confused with conidia that are produced asexually . Open pollination

See: cross-pollination. Open-pollinated crops

This term is synonymous with cross-pollination. Open-pollinated crops can be divided into those that are obligately cross-pollinated, and those that have an optional self-

pollination. It may be generally assumed that cross-pollinated crops do not tolerate inbreeding, otherwise they would be cultivated as pure lines. However, inbreeding is often employed in order to produce hybrid varieties. Many open-pollinated crops are cultivated as clones, because this is the only way of preserving their agriculturally valuable characteristics. Ophiobolus

Ophiobolus graminis is the old name for Gaumanniensis graminis, the fungus that causes "Take-All" disease of cereals. Opium

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