Abstract
Chromosome associations and chiasma frequencies at first metaphase (MI) were studied in allotetraploid reciprocal hybrids between perennial ryegrass (Lolium perenne, Lp) and Italian ryegrass (L. multiflorum, Lm), and parent autotetraploid perennial ryegrass. Preferential chromosome pairings were assessed in Lp × Lm and Lm × Lp hybrids. The reciprocal hybrids were found to have significantly higher frequencies of bivalent pairing and lower frequencies of quadrivalent pairing and chiasmata. The mean frequencies of total bivalents at MI were 6.820, 9.885 and 10.040 and total quadrivalent frequencies were 3.320, 1.775 and 1.760 in the autotetraploid parent and the Lp × Lm and Lm × Lp hybrids, respectively. The frequencies of chiasmata were 25.075, 23.455 and 23.315 in the parent and the Lp × Lm and Lm × Lp hybrids, respectively. The frequencies of preferential chromosome pairing in the Lp × Lm and Lm × Lp hybrids were 42.69 and 44.85%, respectively and the results indicate a significant degree of preferential bivalent association in the hybrids. An inverse relationship was found between the frequency of total bivalent and quadrivalent associations in the parent and the Lp × Lm and Lm × Lp hybrids. These reciprocal hybrids are potentially important breeding materials for developing new hybrid cultivars.
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