Production of Polyploids and Unreduced Gametes in Lilium auratum × L. henryi Hybrid

Intergenomic F(1) hybrids between L. auratum x L. henryi and their BC(1) progeny were investigated through genomic in situ hybridization technique (GISH) to determine their potential value in lily breeding. We confirmed that F(1) intergenomic hybrids possessed a set of chromosomes (x=12) from both parents and that flowers of the F(1) auratum × henryi hybrid showed an intermediate morphological phenotype. Pollen size, viability and germination ability were measured through microscopic observations. F(1) intergenomic hybrids produced a relevant frequency of 2n-gametes, which were successfully used to perform crosses with Oriental hybrids, resulting in the triploid Oriental Auratum Henryi (OAuH) hybrid. Twenty BC(1) plants were generated by crossing between four different Oriental hybrid cultivars and F(1) AuH hybrids using an in vitro embryo rescue technique, after which the genome constitution and chromosome composition were analyzed by GISH. All plants were triploid, showing 12 from female parents (diploid Oriental hybrid) and 24 from male parents (diploid F(1) AuH hybrid). Overall, 16 out of 20 BC(1) progeny possessed recombinant chromosomes with 1-5 crossover sites per plant. Cytological analysis of 20 BC(1) plants by GISH verified that the occurrence of 2n pollen formation in all F(1) AuH hybrids was derived from the FDR (first division restitution) mechanism, in which the genome composition of all BC(1) plants possess 12 Oriental + 12 L. auratum + 12 L. henryi chromosomes. Allotriploids derived from the AuH hybrid were used as female for crossing with the diploid Oriental hybrid cultivar 'Sorbonne' and considerable numbers of plants (0-6.5 plants per ovary) were only obtained when female OAuH (BC(1)) triploids were used. Taken together, the results of this study indicate that production and analysis of F(1) AuH hybrids and their progeny through sexual polyploidization can be useful for efficient creation of important horticultural traits.