A molecular cytogenetic analysis of chromosome behavior in Lilium ...

Chapter 6The results presented in this thesis mainly focus on the analysis of chromosome behaviour inlily hybrids, including interspecific F1 hybrids as well as backcross progenies, usingmolecular cytogenetic techniques. It has been found that 1) there were no chromosomerearrangements in neopolyploids of Lilium hybrids (Chapter 2); 2) the intergenomicrecombination, which has been found in sexual polyploidized backcross progenies, originatedfrom chiasmata formation and crossing over during meiosis (Chapter 2 and 3); 3) meioticabnormalities, such as non-homologous chromosome pairing involved in multivalents and(few) bivalents, were due to the existence of a reciprocal translocation in the paternal parent‘Connecticut King’; 4) chromosome breakage and anaphase bridging were found to be thecause of chromosome structure variation (Chapter 4); 4) isochromosomes were produced dueto the irregularity of meiosis in the interspecific hybrids of lily (Chapter 5). Such results donot only contribute to fundamental research in allopolyploid evolution and speciation, but canalso benefit plant breeding by solving problems in genetic mapping. In this Chapter, sometopics namely:1) Interspecific hybrids of lily: a model for molecular cytogenetic research2) Chromosome rearrangements and its relevance to genetic mapping3) Sexual polyploidization and its significance in polyploidy mapping4) Meiotic abnormalities in lily interspecific hybrids5) Crossing over and introgression breeding6) Genomic shock, isochromosome formation and B chromosome origin during sexualpolyploidizationwill be discussed and future perspectives will be presented to draw more attention to thetheoretical and practical aspects of homoeologous chromosome interaction.Interspecific hybrids of lily: a model for molecular cytogeneticresearchConventional diploid lily cultivars are being replaced by recently produced polyploidycultivars. The genus Lilium consists of about 80 species and has been classified into 7botanical sections (Comber 1949; De Jong 1974). A noticeable feature is that interspecificcrosses within each section are relatively easy and the resultant hybrids are generally fertile,while crosses between species from different sections are difficult because of the existence ofpre- and post- fertilization barriers (Van Tuyl and Lim 2003). As a result, a number of hybridgroups which show distinct morphological characteristics have been bred throughconventional crossing methods (McRae 1998). However, neopolyploids, derived frominterspecific (between sections) hybridization and polyploidization, are playing a prominentrole in lily breeding with the aim of combining desirable traits of different hybrid groups (VanTuyl and Lim 2003). With the advance of technology, barriers of interspecific hybridization72