Yehoshua Anikster and Moshe Feldman
Moshe Feldman and Mordechai E. Kislev
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.
Li Huang, Eitan Millet, Junkang Rong, Jonathan F. Wendel, Yehoshua Anikster and Moshe Feldman
RFLP diversity in the nuclear genome was estimated within and among Israeli populations of wild emmer wheat (Triticum turgidum var. dicoccoides) from a long-term study site at Ammiad (NE Israel), and from several other geographical locations. Using 55 enzyme-probe combinations, high levels of genetic diversity were revealed in wild emmer in general and within the Ammiad site. In spite of high diversity, observed heterozygosity was low and populations consisted of a patchwork of alternate multilocus homozygotes, consistent with the reproductive biology of a predominant self-fertilizing species. Retention of genetic diversity in wild emmer may be promoted by large population sizes, microhabitat diversity, and occasional gene flow through both pollen and seed. Population genetic structure in wild emmer appears to have been influenced by historical founder events as well as selective factors. Multivariate analyses indicated that individuals tend to cluster together according to their population of origin, and that there is little geographical differentiation among populations. Sampling of 12 domesticated land-races and both primitive and modern cultivars of T. turgidum revealed high levels of diversity and a large number of alleles that were not detected in the wild emmer populations. This may reflect a long-term domestication process in which wild, semi-domesticated, and domesticated types grew sympatrically, continuing introgression from wild populations, and perhaps also gene flow from trans-specific sources.