Subsistence farming

Farming which feeds the farmer and his family but produces few surpluses for sale. The converse is usually called commercial farming. Similarly, one speaks of subsistence crops and cash crops. Almost all subsistence farming is now in the tropics. Subsistence crops are often mixtures of several different species , and each species is usually cultivated as a landrace. Subsistence crops are thus genetically diverse, and genetically flexible. Because they are cultivated without any use of pesticides , they have high levels of horizontal resistance. However, their yields and quality are usually considerably less than the modern cultivars of commercial farming. Subsistence crops are thus about half way between a commercial crop pathosystem and a wild pathosystem. Subsystem

A lower systems level. Thus, a functioning gene-for-gene relationship constitutes the vertical subsystem of a plant pathosystem, which is itself a subsystem of an ecosystem. Succulent

In a botanical context, a succulent is a drought-resistant plant that usually contains a considerable store of water. This store is usually protected with very sharp spines, or some form of toxin or deterrent taste. Cacti are typical succulents. Sucker

An underground shoot arising from either from the roots or the subsurface stem of a tree or shrub. Suckers are often an important means (occasionally the only means, e.g., date palm) of vegetative propagation . Sucking bugs See: Miridae. Sugar

The sugars are sweet-tasting, soluble, crystalline carbohydrates. There are a number of different sugars in the human diet, the most common being sucrose, extracted from either sugarcane or sugar beet. Sugar beet

See: Beta vulgaris. Sugarcane

See: Saccharum officinarum.

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