Chromosome pairing in Lolium perenne x L. temulentum diploid hybrids: genetic and cytogenetic evaluation

A Lolium perenne genotype (E5/2/5/10), which had been selected for low chia sma frequency over a number of generations and which was suspected of conta ining one or two heterozygous dominant genes with a significant effect on c hiasma frequency, was crossed with L, temulentum (Ba3081) to create a hybri d population of 47 diploid plants. The mean chiasma or paired arm (PA) freq uency of homoeologous chromosomes at meiosis in the population was 9.1/cell (1.3 PA/chromosome pair) with a distribution skewed towards high PA freque ncy. More than 90% of the hybrid chromosomes paired at meiosis in spite of the disparity in chromosome length and DNA quantity between the two species . Overall, the distribution of PAs between chromosomes for a given number o f PBs/cell favoured the production of rod bivalents over ring bivalents and univalents, indicating that there is a mechanism present that maximizes th e total number of bivalent associations formed. Molecular marker analysis u sing AFLPs and isoenzymes did not identify any clear major gene effect on P B frequency in the hybrid population. It was concluded that the control of PA frequency in E5/2/5/10 was not a simple genetic mechanism.