Not available – first paragraph follows: Hybridization between cultivated species and related wild species has been of great value for cultivar improvement. Genes that enhance the survival of the wild species by providing disease or insect resistance, salt tolerance, cold tolerance, and the like, often confer the same trait on the cultivar to which they are transferred. Fertility barriers restrict the number of wild species that can contribute genes to any particular cultivated species through normal sexual crosses, but these fertility barriers can often be overcome through the use of special procedures.