Hybridization of Senecio squalidus and S. viscosus and Introgression of Genes from Diploid into Tetraploid Senecio Species

Natural triploid hybrids (Senecio × londinensis Lousley) between S. squalidus L. (2n = 20) and 5. viscosus L. (2n = 40) are fairly frequently found in Britain. Under glasshouse conditions both natural and artificial hybrids displayed very low levels of seed fertility and gave rise to morphologically diverse F2 plants at about the triploid or pentaploid chromosome levels. By the F4 generation, progeny of a F2 pentaploid plant had somatic chromosome numbers near to the tetraploid level and considerably increased pollen and seed fertilities. Such fertile tetraploid segregants of S. × londinensis permit the introgression of S. squalidus genes into S. viscosus, and may indicate the course of introgression into other tetraploid species of Senecio.