The effect of B chromosomes on homoeologous pairing in species hybrids

Six diploid populations of Lolium rigidum were used in crosses with a standard homozygous line of Lolium temulentum in order to analyse the variation in the effect of B chromosomes on homoeologous pairing in the interspecific hybrid. — Large differences in chiasma frequency were found, both between the progeny of the different populations and, in one case, between the progeny of different plants from the same population. That this variation was due to differences in B chromosome genotype was ruled out by the use of appropriate 1B Lolium rigidum parents. It is concluded therefore that the effect of B's on homoeologous pairing in this interspecific hybrid can be modified quite substantially by the A chromosome genotype of the parents.