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The origin of wheat and its relationship to jointed goatgrass

Stephen Baenziger
Plant Breeder
University of Nebraska
1992 Wheat Technology Conference
The origin of common wheat (Triticum aestivum L.) remains a mystery with many parts of its history unknown. However, the best information currently available indicates that a progenitor (ancestral) species in the Middle East evolved into various diploid (having two genomes where a genome is a complete set of chromosomes) genera and species. Among these diploid genera and species are: the ancestors of durum and common wheat, rye, barley, and numerous botanical grasses. This evolutionary process is known as divergent evolution (one species evolving into many species). After divergent evolution, a reverse process began known as convergent evolution. In this process, many of the diploid species hybridized and formed polyploids (having more than two complete genomes).The best example of an early polyploids is durum wheat (Triticum turgidum) which has four genomes. Another example is jointed goatgrass (Triticum turgidum) which has four genomes. Another example is jointed goatgrass (Triticum cylindricum, also called Aegilops cylindrica) which also has four genomes. Common wheat is a later polyploid nature of wheat is that it is obvious it can and has crossed with different grass relatives.

Jointed goatgrass can and does spontaneously cross with wheat. As wheat is self-pollinated, these crosses are extremely rare. However, under conditions that lead to male sterile wheat (stress, frost, hybrid production fields, etc.) crossing levels will be higher. The hybrid between jointed goatgrass and wheat is usually sterile, though the sterile hybrid can then be crossed by wheat and form seed. Fortunately, goatgrass has barriers to hybridization and later generations are almost always sterile. Because there is so much wheat in relation to jointed goatgrass, most of the hybrids are between wheat as a female and jointed goatgrass as male. Hence genes from jointed goatgrass are diluted in the wheat. Little information is available on hybrids between jointed goatgrass as a female and wheat as a male. In this case, the wheat genes could be transferred to jointed goatgrass which could be harmful if they were for herbicide resistance or improved the weed’s survival.

Two questions are usually asked about wheat and jointed goatgrass: 1. Will wheat or jointed goatgrass breakdown and release its progenitor species? and 2. If the origin of wheat and jointed goatgrass are from the middle east, how did they get to the united states? The answer to the first question is no. Wheat (or for that matter the manmade hybrid, triticale) will not breakdown into to its progenitors. Wheat (and triticale) are reproductively stable. As for the second question, wheat was brought to the United States by immigrants. In the wheat seed there was also seed of common weeds, in this case jointed goatgrass.