Diverse chromosome complements in the functional gametes of interspecific hybrids of MT- and A-karyotype Lycoris spp.

The karyotype and numeric changes in chromosomes among taxa of Lycoris (spider lilies) have been attributed to whole-arm rearrangements; however, the history of karyotype evolution of Lycoris is still ambiguous. In the natural habitat, one-third of Lycoris taxa are interspecific hybrids that are mainly sterile and extremely diverse in morphologies. Lycoris are geophytes with the reproductive stage initiated inside the bulbs during the storage period, which brings some inconveniences in collecting meiotic materials for studying chromosome pairing. The partial fertility of an artificial F1 interspecific hybrid between L. aurea (2n = 14) and L. radiata (2n = 22) provides an alternative option for tracing the meiotic process in F1 hybrids. The chromosome compositions of those functional gametes generated by the F1 hybrid could be recovered according to the chromosome complements of backcross progenies. We perform genomic in situ hybridization (GISH) analysis on somatic chromosomes of 34 BC1 plants (2n = 14–22) to reveal chromosomal divergences in number and composition of those functional gametes. GISH results also indicated a high homology between the MT- and A-genomes of Lycoris, reflecting on the partial fertility and frequently homoeologous recombination at meiosis of the F1 interspecific hybrids. The diverse chromosome complements and recombinant patterns presented in these functional gametes suggested that interspecific hybridization is an important force in driving diversification among Lycoris species. We suggest that the MT-karyotype genome may be the ancestral type in Lycoris, and some other chromosomal rearrangements in addition to centromeric fission may have played roles in the karyotype evolution of Lycoris.