MEIOSIS IN THE LEEK (ALLIUM-PORRUM L) REVISITED .2. METAPHASE-I OBSERVATIONS

A detailed analysis of metaphase I of meiosis in pollen mother cells o f Allium porrum has confirmed that despite frequent quadrivalent pairi ng (71 per cent) at prophase I and a high mean chiasma frequency (3.5 per tetrasome), the majority of quadrivalents are resolved into bivale nt associations at metaphase I. The present observations also support the view that quadrivalent resolution results from the pronounced prox imal chiasma localization found in this species. However, neither chia sma localization nor quadrivalent resolution are as prevalent as most previous reports have indicated. About 2 per cent of chiasmata, consid erably more than in previous studies, occur in nonproximal chromosome regions in this material, while 12.9 per cent of metaphase I cells con tained one or more multivalents, again exceeding most previous estimat es. Meiotic regularity in this material was also disturbed by an unexp ectedly high frequency of univalents. Overall 25.8 per cent of cells c ontained one or more univalent pairs, giving an overall mean of 0.32 u nivalent pairs per cell. It appears that meiosis in the leek is less r egular than previous reports have indicated. The implications for fert ility, stability and uniformity are not trivial and ought to be consid ered in the context of leek production and breeding.