Autopolyploid induction via somatic embryogenesis in Lilium distichum Nakai and Lilium cernuum Komar

Abstract

New ornamental varieties of high quality can be created via artificial polyploid induction. In the present study, the first system of polyploid induction with somatic embryogenesis of Lilium distichum Nakai and Lilium cernuum Komar. was developed. Somatic embryos were cultured on MS with 0.41 μmol L−1 picloram and 1.07 μmol L−1 NAA by scales (5 mm2). After 40 days, somatic embryos were transferred to MS with 2.21 μmol L−1 BA for somatic embryogenesis. As determined from observations of paraffin sections, embryonic cells of L. distichum originated from outer cells at first, and somatic embryogenesis occurred through an indirect pathway. In L. cernuum, embryonic cells originated from inner cells at first, and somatic embryogenesis occurred through a direct pathway. Polyploids were successfully formed from somatic embryos and scales by the soaking and mixed culture methods with different colchicine concentrations (0.01%, 0.05%, and 0.1%; v/v) and durations (24, 48, and 72 h). The polyploid induction rate reached 57.14% and 46.15% with 0.05% colchicine treatment in L. distichum (48 h) and L. cernuum (24 h), respectively. Tetraploids (28.57% and 23.08%) and aneuploids without chimeras among the obtained polyploid plantlets were identified by chromosome counts of root-tip tissue squashes in L. distichum and L. cernuum. Tetraploid plantlets of L. distichum exhibited broader leaves, longer guard cells, larger stomata and higher stomatal conductance than diploid plantlets. Tetraploid plantlets of L. cernuum showed 1.76 × higher chlorophyll content, significantly more leaves, longer guard cells, larger stomata and lower stomatal conductance than diploid plantlets. For the first time, we established a somatic embryogenesis system for L. distichum and L. cernuum using somatic embryos and scales to induce polyploids by soaking and mixed culture. Combinations of colchicine concentrations and periods of time were compared to select the best treatment combination. Comprehensive morphological observations, stomatal observations and root-tip tissue squashes were used to identify the ploidy of doubling plants. Our results provide a foundation for improving the ornamental value of two wild lily species, creating new Lilium germplasm and improving the reproduction coefficient of these resources.