HOW MANY TOUGH-RACHIS MUTANTS GAVE RISE TO DOMESTICATED BARLEY

It is commonly agreed that cultivation of wild barley preceded the sel ection of the domesticated, non-brittle spike type. However, how commo n was wild barley cultivation before domestication and how many domest icated mutants gave rise to the barley crop could not be inferred from botanical and archaeological evidence. Some clues, nevertheless, can be obtained from the pattern of allozyme diversity in wild and cultiva ted barley obtained by Kahler and Allard (1981). Parallel variation, i n terms of number of alleles per locus and frequency of the various al leles, was found in wild and domesticated barley. This similarity has been taken as an indication of multiple domestications and the frequen cy of the rarest alleles has been used to estimate that about 100 toug h-rachis different mutants were necessary for the inclusion of the all ozyme diversity of the wild barley in the domesticated crop. Assuming mutation rate of 10(-6) in the locus governing tough rachis, the plant population required to generate these 100 mutants in one year would e xtend over about 200 hectares, or 10 hectares if the 100 mutants have been formed over a period of 20 years. The simplified calculations sug gest that prior to domestication cultivation of wild barley was not a common practice.