The cytology of the genus Briza L. (Gramineae)

Meiosis has been studied in five European and four South American species of Briza. The various species have different chiasma frequencies and different patterns of chiasma localisation. Population studies show that there are significant differences in mean plant chiasma frequency between populations of B. maxima whereas B. media and B. spicata do not show interpopulation differences. B. media is shown to have diploid and autotetraploid races and the distribution of these chromosome races in Europe has been plotted. The South American species studied are all bivalent forming tetraploids and would therefore appear to have an allopolyploid origin. Interchange heterozygosity has been found in B. media and B. elatior, different populations of B. media have been shown to be heterozygous for different interchanges. These topics are discussed in relation to the regulation of recombination.