Seed production

See: Seed industries. Seed testing

Seed offered for sale is usually tested in a seed testing laboratory. The main test is for germination percentage, but other tests can include seed health, freedom from weed seeds, identity and purity of cultivar, etc. Seed-borne parasites

Some parasites are carried in the seed, both true seed and vegetative seed tubers etc. True seed can be contaminated, infected, or infested. Contaminated seed carries pathogen externally and these can be destroyed by seed dressings. Infected seed carries pathogens internally and can be disinfected by heat treatment. Infested seed carries post-harvest insects. However, seed-borne parasites are the exception rather than the rule and the use of true seed eliminates most parasites.

In the cereals, loose smuts produce infected seed, while covered smuts produce contaminated seed.

Seed tubers, setts, etc that are used for vegetative propagation will carry any parasite that happened to invade the parent plant. This explains why the need for seed health certification is so much more important with crops that are vegetatively propagated, and which have suffered a major vertifolia effect because of inappropriate breeding. Segregation

In plant genetics, the term 'segregation' refers to the separation of specified traits within the population of the next generation. Selection

The selection of individuals within a plant population can be positive or negative. Positive selection identifies the individuals to be kept, usually as parents of the next breeding cycle. Negative selection identifies individuals that must be eliminated, or at least prevented from producing pollen, to ensure that they are not represented in future generations.

These terms can also be applied to selection within variable populations of tree crops. For example, a cocoa plantation might be suffering from witch's broom disease (Crinpellis perniciosa). A positive selection would identify the most resistant trees for propagation in a new plantation. A negative selection would identify the most susceptible trees for elimination, on the grounds that they were causing severe parasite interference, and their removal would greatly reduce the overall disease incidence. Selection coefficient

The proportion of plants selected in the screening population during recurrent mass selection . A selection coefficient of 10% means that the best 10% of the plants in the screening population are kept to become parents of the next generation. Selection coefficients of 1% and 0.1% are often used, and they exert very strong selection pressures. Selection pressure

Pressure (in the sense of coercion, persuasion, or bringing pressure to bear) that induces changes in the genetic composition of a mixed population. The mechanism of selection pressure is that the fittest individuals have a reproduction advantage, while less fit individuals have a reproduction disadvantage. Thus, in the face of parasitism, resistant individuals are advantaged, while susceptible individuals are disadvantaged. Selection pressures can function only in a population that is genetically diverse and genetically flexible.

Selection pressures can be either natural (i.e., in a wild ecosystem) or artificial (i.e., in a plant breeding program). The term selection pressure usually refers to micro-evolution. Natural selection pressures produce new ecotypes, and artificial selection pressures produce new agro-ecotypes, or cultivars. Selection pressures can be positive or negative. Positive selection pressure leads to the accumulation of a quantitative variable (e.g., horizontal resistance) that is deficient, while negative selection pressure leads to the decline of a variable that is excessive or otherwise unnecessary (e.g., horizontal resistance in the absence of a parasite). See also: Vertifolia effect. Selection, family

See: Family selection. Self-compatible

Flowers, or plants, that are self-compatible are able to pollinate themselves. See also: Self-incompatible. Self-fertile

See: Self-compatible.

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