Ecogeography, genetic diversity, and breeding value of wild emmer wheat (Triticum dicoccoides Korn ex Asch & Graebn.) Thell.

Wild emmer wheat (Triticum dicoccoides Korn ex Asch. & Graebn.) Thell. is the allotetraploid (2n=4x=28; genome BBAA) progenitor of cultivated wheat. It is fully compatible with the tetraploid (BBAA) durum wheat (Triticum durum), and can be crossed with the hexaploid (2n=6x=42; BBAADD) wheat (Triticum aestivum). In the Fertile Crescent, the centre of origin and centre of diversity of wild emmer wheat, the wild progenitor exhibits a wide phenotypic and genotypic variation and displays a rich adaptive genetic diversity which is ecologically and genetically structured as an "archipelago." The fertile hybrids between wild emmer wheat and domesticated durum wheat point to the early, and probably current, extensive gene flow that must have enriched the genetic structure of both subspecies in the Fertile Crescent. Specific alleles and allele combinations predominate, at the macro-and microgeographic scales, as co-adaptive blocks of genes adapted to diverse biotic and abiotic stresses. Wild emmer wheat is recognized as a source of genes for agronomically important traits. These include genes for large spike and grain size, high grain and protein yield, desirable composition of storage proteins, photosynthetic yield, herbicide response, salt tolerance, drought tolerance, disease (leaf rust, stripe rust, powdery mildew, and soil-born mosaic virus) resistance, profuse tillering, and genes for other quantitative traits. For millennia, the vast genetic diversity in wild emmer wheat must have contributed to the spatially and temporally sustainable wheat production as a major component of dynamic cropping systems in the Fertile Crescent. With the advent of, and easy access to, molecular genetics and breeding tools, wild emmer wheat is expected to contribute the full range of its diversity in quantitative and qualitative traits for a more globally sustainable wheat production. It is expected that the current and future detailed records of phenotypes and genotypes and their spatio-temporal variation patterns in the Fertile Crescent will form an integral part of a relational database that can serve future strategies for in situ conservation, collection, evaluation, and utilization by wheat geneticists and breeders.