Enrichment of Breeding Germplasm

Related species provide adaptation to a wide range of soils and climates, making them historically important as regional rootstocks. Utilization as rootstocks ranges from top-working naturally occurring species trees to propagating related species and species hybrids specifically for commercial use. The breeding of interspecies hybrids that combine the strengths of different species into commercial rootstocks has become increasingly important as almond orchards become more highly managed, to the extent that most modern almond rootstocks are hybrids of two or more species. The interspecies germplasm can be further backcrossed in cultivar breeding programs to introduce useful traits that are not present in more traditional breeding materials. Recent achievements in almond cultivar improvement include the transfer of self-fruitfulness from a closely related species to cultivated almonds, as well as improved nut quality.