Abstract
Colchicine-indced polyploids derived from Oenothera (subgenus Raimannia) diploids with meiotic chromosome configurations 7 pairs, _??_ 10, 2 paris, _??_ 10, _??_ 4, and _??_ 14, were used to study chromosome behaviour of tetraploids in relation to structural heterozygosity. Tetraploid plants showed “gigas” features of morphology related to increased cell size; in octoploids, there was a further increase in cell size but overall size and vigor was reduced and they were infertile.
Cytologically, all tetraploids showed a reduction in chaisma frequency. Meiotic irregularities of tetraploids and octoploids were similar to those found occasionally in diploids but occurred more frequently. Tetraploids derived from the structurally homozygous diploid race showed quadrivalents, trivalents, bivalents and univalents; those derived from completely structurally heterozygous diploids showed a range of chromosome configurations from univalents, through ring pairs and intermediate chains and circles to ch20. Intermediate tetraploids showed an intermediate configuration range although some differences between them could not be related to differences in their diploid progenitors and it was concluded that although chromosome behaviour of tetraploids is largely determined by the degree of structural heterozygosity of the diploid progenitor, the genetic makeup of a race may modify this behaviour.
In tetraploids there was a fertility decrease in pollen and seed set except for pollen of O.mollissima Cayrasco where percentage sterile grains was unchanged; tetraploids derived from structurally heterozygous diploids showed a smaller fertility reduction than those derived from the homozygous diploids.
