Hybrid Breeding

Hybrid breeding takes advantage of the heterosis effect. This effect means that offspring of a crossing has higher yields than the respective parent lines. For hybrid breeding, inbred male and female lines are developed which are as different as possible. These true-breeding (homozygous) lines will then be crossed with each other. 

In order to make sure that the inbred line used as mother parent will only be pollinated by the inbred father parent line, self-pollination must be precluded. To ensure this, castrated or male sterile lines (lines not producing own pollen) are used as mother parent. Unisexual maize e.g. lends itself to manual castration of the mother plant by simply removing the tassels. In species with bisexual flowers (e.g. oilseed rape or rye), genetic sterility mechanisms are being applied.

The offspring of the crossing of the inbred lines are hybrids. Heterosis, i.e. superior performance, will only be strong in this first generation. As a consequence of Mendel's second Law of Segregation, it will already be lost in the next generation. 

Up to now, hybrid breeding has been used mainly for open-pollinating species (maize, oilseed rape, sunflower, rye and sugar beet).