Origin, Genetic Diversity and Evolution in Almond Tree

Almond (Prunus dulcis [Mill.] D. A. Webb) originated in Central Asia and later got distributed to Persia, Mesopotamia, and, via trade routes, to the European primitive civilisations, with the Mediterranean Basin being considered its centre of diversification. Selection throughout the centuries has led to a larger and sweeter kernel—the edible part of the fruit. The first ex situ collection of almonds was described at Yalta (Russia) in 1935 followed by California (US), France, Spain, Italy, Portugal, Greece and in general all the Mediterranean or countries with a Mediterranean climate. More than 1500 almond cultivars are maintained in the germplasm collections worldwide, with 80% of the diversity being held among the Asian and European banks. The almond genetic diversity was studied first using microsatellites or simple sequence repeats (SSRs) and amplified fragment length polymorphism (AFLPs), followed by single nucleotide polymorphism (SNP) markers, culminating in the publication of the almond genome sequence in 2020. Breeding efforts in almond cultivars have extensively pursued late blooming and pollen self-compatibility, and more recently tree architecture and disease resistance. Rootstock breeding programmes have mainly focused on the resistance to biotic and abiotic stresses and interspecific hybrids of almond, peach and other Prunus species are used as rootstocks all over the almond growing regions. Apart from Central Asia and the Mediterranean Basin, the cultivation of almonds extends nowadays to many regions with warm climates like California, Argentina, Chile, South Africa and Australia.