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Morphological Evidence Concerning the Origin of the B Genome in Wheat

P. Sarkar and G. L. Stebbins
American Journal of Botany
Vol. 43, No. 4 (Apr., 1956), pp. 297-304
Stable URL: http://www.jstor.org/stable/2438947
Page Count: 8
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Morphological Evidence Concerning the Origin of the B Genome in Wheat
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Abstract

Morphological comparison between both cultivated and wild members of the T. monococcum (einkorn) group of wheats on the one hand and the tetraploid emmer wheats on the other, followed by the use of Anderson's method of extrapolation, indicates that the emmer wheats arose as amphiploids between the diploid einkorns and another species or species group having the following characteristics: rachis internodes long and narrow; spikelets with 3 or more florets; glumes with one inconspicuous keel, with more than 6 veins, with the tip 1-toothed, and with a thick margin; lemmas all long awned, the shoulder inconspicuously dentate or blunt; the palea not splitting at maturity; the grain large, thick, and grooved. These characters are all approached or equalled by Aegilops speltoides var. ligustica. The hypothesis is therefore advanced that the tetraploid emmer wheats evolved from amphiploids between T. monococcum and its relatives on the one hand and various diploids similar to A. speltoides on the other. The amphiploidy is believed to have occurred several times, and to have been followed by evolution on the tetraploid level which consisted of hybridization between different raw amphiploids, accompanied by chromosome rearrangements and gene mutation. In this way, it is postulated that the monococcum type A and the speltoides type S genomes became modified to form the A and B genomes of the modern emmer as well as the hexaploid wheats.

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