An hybrid cultivar is an individual cross-bred from parents that are not closely related.

The parents may be individuals of different species (e.g. horse mare and donkey stud yield a mule) or they may be plants of the same species that have been inbred and possess genes for important traits, known as an “inbred line”.  This is a commonly used practice in plant breeding.

A plant variety always derived from the same two inbred lines is known as a hybrid cultivar. Hybrids are superior to their parents based on a principle called heterosis (hybrid vigour). They possess a higher repertoire of genetic information and are often larger and more resistant to disease. Maize and sugar beet are almost exclusively cultivated as hybrid cultivars.

Breeding hybrid cultivars and producing hybrid seed is a complex process. Because most plants have both male and female sexual organs, self-pollination is a possibility that must be prevented. This usually entails removing the male flower parts from plants that will be used to produce seed.

• Collecting hybrid seed from male-sterile lines facilitates this process. Today, such lines can be created by genetic engineering. To produce fertile offspring from these lines, a gene is inserted into the crossing partner which reverses the sterility.
  
• Inducing male sterility by genetic engineering is possible for crops such as rapeseed and chicory.