Meiosis in the leek (Allium porrum L) revisited .2. Metaphase I observations

A detailed analysis of metaphase I of meiosis in pollen mother cells of Allium porrum has confirmed that despite frequent quadrivalent pairing (71 per cent) at prophase I and a high mean chiasma frequency (3.5 per tetrasome), the majority of quadrivalents are resolved into bivalent associations at metaphase I. The present observations also support the view that quadrivalent resolution results from the pronounced proximal chiasma localization found in this species. However, neither chiasma localization nor quadrivalent resolution are as prevalent as most previous reports have indicated. About 2 per cent of chiasmata, considerably more than in previous studies, occur in nonproximal chromosome regions in this material, while 12.9 per cent of metaphase I cells contained one or more multivalents, again exceeding most previous estimates. Meiotic regularity in this material was also disturbed by an unexpectedly high frequency of univalents. Overall 25.8 per cent of cells contained one or more univalent pairs, giving an overall mean of 0.32 univalent pairs per cell. It appears that meiosis in the leek is less regular than previous reports have indicated. The implications for fertility, stability and uniformity are not trivial and ought to be considered in the context of leek production and breeding.