Embryogenic cultures of lily (Lilium spp.): optimising callus initiation, maintenance, and plantlet regeneration

Summary

To facilitate genetic improvement in lily (Lilium spp.), the efficiency of regeneration from callus cultures induced from a range of explants was optimised for three important cultivars: Oriental hybrid lily ‘Sorbonne’, Oriental hybrid lily ‘Bernini’, and Oriental × Trumpet hybrid lily ‘Robina’. Filaments, pedicels, styles, ovaries, and anthers were used as explant material to identify and optimise the parameters that influence somatic embryogenesis. The results showed that embryogenic competence was dependent on cultivar, explant type, and developmental stage. The highest numbers of embryogenic cultures were induced from filaments of ‘Sorbonne’ (22.8%), ‘Bernini’ (16.5%), and ‘Robina’ (17.8%). The youngest filaments (developmental Stage I) gave the highest embryogenic response in each genotype, showing a three-to-four-fold increase compared with Stage V explants. Of the three regions of the filament used as explants, only the basal region produced embryogenic cultures. The highest proliferation frequency of embryogenic callus was obtained on 1.0× Murashige and Skoog (MS) medium supplemented with 2.0 mg l^–1 picloram (PIC; 4-amino-3,5,6-trichloropicolinic acid) and 60 g l^–1 sucrose. These cultures also produced the highest numbers of regenerated plantlets when transferred to plant growth regulator (PGR)-free 1.0× MS medium supplemented with 1.0 g l^–1 activated charcoal (AC) and 30 g l^–1 sucrose. Histological and scanning electron microscopic (SEM) observations of the various developmental stages of somatic embryo development showed the four typical stages: globular, heart-shaped, torpedo, and cotyledonary.