CHROMOSOME-PAIRING AND CHIASMA FORMATION IN AUTOPOLYPLOIDS OF DIFFERENT LATHYRUS SPECIES

Chromosome pairing and chiasma formation were studied in natural and i nduced tetraploids (2n = 28) of Lathyrus odoratus (induced), Lathyrus pratensis (natural and induced), Lathyrus sativus (induced), and Lathy rus venosus (natural), as well as in triploids of L. pratensis and dip loids of L. odoratus, L. pratensis, and L. sativus. All natural tetrap loids appeared to be autotetraploids and their meiotic metaphase I beh aviour was very similar to that of the induced autotetraploids, with a verage numbers of pairing partner switches exceeding 4 or even 5. Mult ivalent frequencies were high, but the numbers of chiasmata were not m uch higher than necessary to maintain the configurations. Interstitial chiasmata were common, but not predominant. Fertility was reduced, bu t sufficient for predominantly vegetatively reproducing species. The t riploids of L. pratensis had an even higher multivalent frequency than the tetraploids, but still produced some viable progeny at or close t o the tetraploid level, suggesting that in mixed populations of diploi ds and tetraploids, triploids can contribute to gene flow between the ploidy levels. There was no significant correlation between chiasma fr equency and ring bivalent frequency in the diploids and multivalent fr equency in the corresponding tetraploids. In the tetraploids, chiasma frequency and multivalent frequency were negatively correlated.