U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska
Date of this Version
M.L. Badenes and D.H. Byrne (eds.), Fruit Breeding, Handbook of Plant Breeding 8, 771; DOI 10.1007/978-1-4419-0763-9_20.
The pecan, Carya illinoinensis (Wangenh.) K. Koch, is the most economically important member of the Carya genus and is the most valuable native North American nut crop. The Carya genus is a member of the walnut family, Juglandaceae, and comprises 20 species. Over 98% of the world’s annual pecan production is produced in the southern USA and northern Mexico. Pecan is a diploid (n = 16), monoecious, long-lived tree species. Owing to its heterodichogamy, pecan is primarily cross-pollinated, resulting in high heterozygosity with severe inbreeding depression when selfed. Establishment of commercial pecan orchards during the nineteenth century was mainly by planting open-pollinated nuts from mother trees possessing desirable characteristics. These orchards consist of trees with widely varying production and quality attributes due to the heterozygosity of pecan. Vegetative propagation became popular ca. 1900, and most newly planted orchards consist of a chosen combination of clonally propagated superior varieties. Clonally derived orchards are more productive and produce nuts of much higher quality than remaining native or seedling orchards. Thirteen Carya species, including pecan, are native to the USA. The National Clonal Germplasm Repository for Pecans and Hickories which preserves over 300 pecan cultivars, landraces, and species accessions was established in 1984 to describe and preserve this underutilized resource. Objectives of pecan breeding are higher yields and nut quality, and resistance to diseases and insects. Pecans are attacked by a wide range of disease and insect pests causing substantial losses to the crop. Various levels of resistance to scab and aphids are available in improved pecan varieties, and breeding programs are focusing on developing new cultivars with high levels of resistance in combination with good horticultural attributes. Another major effort in pecan breeding is the development of earlier maturing cultivars with the potential to bear more consistently over years.