Domestication of emmer wheat and evolution of free-threshing tetraploid wheat

Abstract

We describe here the initial steps of cultivation of wild emmer in the Levant, i.e., the western part of the Fertile Crescent, as well as genetic changes caused by spontaneous mutations, leading to its domestication and to the development of free-threshing tetraploid wheat, Triticum turgidum. Review of archaeological findings from the Pre-Pottery Neolithic A (PPNA) (10,300-9,500 BP; uncalibrated) indicates that wild emmer was first cultivated in the southern Levant. Domesticated emmer (with a nonbrittle spike) appeared several hundred years later in the early PPNB (9,500-9,000 BP), and for a millennium or more was grown in a mixture with wild emmer in many Levantine sites. After the appearance of domesticated emmer, types with naked, free-threshing grains emerged in the late PPNB (9,000-7,500 BP). We support the model in which domestication occurred independently in several sites across the Levant. According to this view, the genes for non-brittleness were transferred to numerous wild emmer genotypes through countless spontaneous hybridizations, followed by human selection. Consequently, domesticated tetraploid wheat evolved as polymorphic populations rather than single genotypes. The relatively wide genetic basis of the young crop has enabled it to tolerate biotic and abiotic stresses and to succeed under cultivation. The archaeological findings of wild emmer cultivation and domestication do not support the idea of development within a small core area, but rather indicate the polycentric origin of agriculture in the Levant.

Keywords:

• free-threshing wheat
• Pre-Pottery Neolithic
• spike non-brittleness
• wheat domestication
• wild emmer
• tetraploid wheat
• Triticum turgidum ssp. dicoccoides
• ssp. durum
• wheat evolution