Exploration of B Chromosome Origin in Allotriploid Lily Associated with Anomalous Meiosis

Supernumerary (B) chromosomes are widespread in numerous plants, including the Lilium genus. However, their origin remains unclear. This study used traditional and modern cytogenetics to analyze the triploid lily cultivar ‘Eyeliner’ (LAA) to identify the microsporogenesis, fertility, and chromosome composition of its progeny and record a case of potential B chromosome formation. The results indicated anomalous meiosis of LAA in all processes. In microspores, different cells had different numbers of chromosomes and fragments. Moreover, the fluorescence in situ hybridization (FISH) results showed that some fragments contained telomere signals at both ends. The LAA × AA progenies were aneuploid, with one progeny containing a small aberrant chromosome (potential B chromosome). The genomic in situ hybridization (GISH) results showed that the aberrant chromosome originated from the L genome. In contrast, the FISH results showed that the aberrant chromosome contained two telomere signals. This suggests that the anomalous meiosis of the triploid lily forms chromosome bridges, fragments, and small aberrant chromosomes (isochromosome), which eventually form aneuploid gametes containing small aberrant chromosomes passed on to the progeny. This study provides a case in which the potential B chromosomes are derived from the A chromosomes.