Interspecific hybridization in Papaver: 1. F1hybrids of P. somniferum with perennial species of sect. Oxytona

The artificial F1 hybrids Papaver somniferum × bracteatum, P. somniferum × orientale and P. somniferum × pseudo-orientale were produced, using various strains of each species. Seed set and germination were lowest in the second and highest in the first combination, but the germination also depended greatly on the P. somniferum strain used. The chromosome numbers counted on the hybrids were 2n = 18, 2n = 25 and 2n = 32, respectively. Morphologically, all the hybrids were more or less intermediate between the parents, but the effect of the paternal species clearly strengthened as their ploidy level rose. Semilethal dwarfism occurred in all three combinations, the frequencies of the dwarf individuals being 53.4, 2.8 and 6.4%, respectively. In all, about 33% of the hybrids flowered towards the end of their first growing season, but most of them produced new basal shoots after flowering. In greenhouse conditions the hybrids from all combinations showed a potential for perennial growth, although they never survived the winter outdoors. Reduced or abnormal flower parts were common in all hybrid combinations, and only about 3—4% of the pollen grains had normal size, shape and stainability. The frequencies of uni-, bi- and multivalents at metaphase I showed that the amount of pairing increased with the ploidy level of the paternal parent, the percentages of paired chromosomes in the three hybrid combinations being 31, 44 and 60, respectively. The chromosomes of P. somniferum show some pairing with those of all three species of sect. Oxytona.