Probing meiosis in hybrids of Lolium (Poaceae) with a discriminatory repetitive genomic sequence

A moderately repetitive genomic DNA sequence (designated pLPBB2-123) derive d from Lolium perenne L. (Poaceae) is considerably more abundant in the gen ome of this species than in that of the closely related L. temulentum. The repetitive sequence probe is clearly able to discriminate between the genom ic DNA of both species in Southern analysis, and effectively 'paints' only the chromosome set of L. perenne in diploid and triploid hybrids with L. te mulentum. Fluorescence in situ hybridisation of this sequence onto homoeolo gous chromosomes during meiosis I of the hybrids shows that the sequence is evenly distributed along all of the chromosomes of L. perenne and appears to have little effect on the structural integrity or recombination potentia l of hybrid bivalents. Discrimination between chromatin of different parent al origin in hybrid bivalents shows for the first time a progressive relaxa tion of relational coiling of homoeologues throughout meiotic prophase. It also highlights structural irregularities that can now be unequivocally ass igned to the longer chromosomes of L. temulentum. The advantages of the use of specific differentially amplified sequences instead of whole genome pro bes are discussed within the context of introgression breeding programmes w ithin the Lolium/Festuca complex.