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A Lolium perenne genotype (E5/2/5/10), which had been selected for low chiasma frequency over a number of generations and which was suspected of containing one or two heterozygous dominant genes with a significant effect on chiasma frequency, was crossed with L. temulentum (Ba3081) to create a hybrid population of 47 diploid plants. The mean chiasma or paired arm (PA) frequency of homoeologous chromosomes at meiosis in the population was 9.1/cell (1.3 PA/chromosome pair) with a distribution skewed towards high PA frequency. 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 of PAs/cell favoured the production of rod bivalents over ring bivalents and univalents, indicating that there is a mechanism present that maximizes the total number of bivalent associations formed. Molecular marker analysis using AFLPs and isoenzymes did not identify any clear major gene effect on PA 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.

A genetic map of Lolium has been produced using isozyme, restriction fragment length polymorphism (RFLP) and random amplified poiymorphic DNA (RAPD) markers applied to a segregating family derived from an F[sub1] hybrid plant of L. perenne × L. multiflorum provenance, crossed on to a doubled haploid L. perenne A total of 106 markers, out of a total of 160 polymorphic loci analysed, have been ascribed to seven linkage groups covering a map distance of 692 CM. Two of these groups may be allocated to chromosomes 2 and 6 of the Loliurn genome. The remaining unallocated markers, the majority of which showed severe segregation distortion, could be associated into small groups of two or three markers which showed no linkage with the main groups at a LOD of 24.8 or, if associated, could not be mapped in a satisfactory manner. This high incidence of disturbed segregations could be accounted for by the use of an interspecific hybrid between two species of differing genome size, with consequent cytological imbalance. [ABSTRACT FROM AUTHOR]