SUPERNUMERARY CHROMOSOMES IN DIPLOID AND TETRAPLOID FORMS OF CRESTED WHEATGRASS

Abstract

Supernumerary chromosomes were present in two diploid introductions of crested wheatgrass but absent in the diploid variety Fairway. In five tetraploid populations, they were present in 36.9 to 88.5% of the plants.Diploid plants contained supernumerary chromosomes in pollen mother cells, in primary roots, and in stem tissues, but not in adventitious roots. Supernumeraries in crested wheatgrass were usually smaller than basic chromosomes and they were not heterochromatic. There was good pairing between supernumeraries but not between supernumerary and A-chromosomes. Transmission of supernumeraries through the egg generally occurred in haploid numbers. In pollen, directed non-disjunction of supernumeraries towards the gametes took place with an average frequency of approximately 70%. The degree of transmission depended to some extent on the genotype of the parent and on the numbers of supernumeraries involved. Elimination of supernumeraries from reproductive tissues was generally low but became more pronounced at higher frequencies.