In 1928 Georgi Karpechenko made first intentional intergeneric allopolyploid Raphanobrassica by crossing radish Raphanus sativus 2n=18 RR with cabbage Brassica oleracea 2n=18 CC, both from Brassicaceae family with similar chromosome numbers. Initial F1 hybrid RC 2n=18 was highly sterile with 9 radish and 9 cabbage chromosomes but no homologous partner for synapsis, showing mostly univalents at metaphase I and abortive gametes. Karpechenko discovered a few fertile seeds where somatic doubling had occurred spontaneously, yielding allotetraploid RRCC 2n=36 containing full diploid sets of both parents. Each chromosome now had exact homolog to pair, regular bivalent formation resumed, and fertility restored substantially. Although agronomically useless because roots like cabbage and leaves like radish opposite to desired combination, experiment proved possibility of creating new species through allotetraploidy, inspiring later synthesis of fertile Brassica hybrids, triticale, and serving as cytogenetic demonstration of allopolyploid speciation mechanism and intergeneric hybridization barrier breakdown via doubling. Karpechenko's experiment inspired later synthesis of Brassica napus, Nicotiana tabacum, and Triticale, demonstrating that hybridization plus whole genome duplication restores fertility and creates instant reproductive isolation from parents, mechanism now recognized as major driver of plant speciation and crop evolution in angiosperms under natural conditions.
Ref:
Karpechenko GD 1928 Z Pflanzenzucht – Raphanobrassica. Stebbins GL. Chromosomal Evolution
