Origin and Domestication of Wild Bitter Almond. Recent Advancements on Almond Bitterness

Almond is one of the oldest species to be domesticated. Wild almonds species accumulate the bitter and toxic compound amygdalin, a cyanogenic diglucoside. The key event enabling almond domestication was the selection of sweet kernel genotypes. Genetic studies demonstrated that the edible sweet almond kernels originated from a dominant mutation, in a locus found in the linkage group five, locus name as Sweet kernel (Sk). In a combination of techniques involving biochemistry, biotechnology, mapping genetics, molecular biology, etc., the Sk gene has been elucidated, codifying for a transcription factor of the bHLH family. A non-synonymous point mutation (Leu to Phe) in the bHLH2 prevents transcription of the two first genes of the amygdalin biosynthetic pathway, the P450 PdCYP79D16 and PdCYP71AN24. With this discovery, a molecular marker has been developed to be used in any almond breeding program, bringing to the field only sweet almond trees.