Evidence for autotetraploidy in Plantago media and comparisons between natural and artificial cytotypes concerning cell size and fertility

The hypothesis of autotetraploidy in Plantago media (2n = 12 and 2n = 24) was tested. The two cytotypes are morphologically very similar. Rare 4X and 3X hybrids were obtained in inter-ploidy crosses. The reproductive isolation between 2X and 4X is post-zygotic and can be broken down and introduced by colchicine treatment. The studied diploid and tetraploid populations shared the same alleles for nine allozyme loci. Together this provides strong evidence for autotetraploid origin of tetraploid P. media. Fertility of colchicine tetraploids was comparable to natural tetraploids and slightly lower than natural diploids. In contrast to colchicine tetraploids, natural tetraploids did not show gigas-characteristics. Tetraploid hybrids between diploids and natural tetraploids showed partial gigas-characteristics. The possible reasons for the differences in cell size between cytotypes are discussed. Differentiating characters between the natural cytotypes were not affected by colchicine treatment and are therefore not a direct consequence of polyploidization.