Chromosome doubling in sterile Syringa vulgaris x S. pinnatifolia hybrids by in vitro culture of nodal explants

The aim was to produce tetraploid forms of hybrids of Syringa vulgaris x S. pinnatifolia to restore fertility and enable further breeding to be undertaken. Excised nodal sections of three selections were pre-cultured for 5 days then treated with a range of colchicine concentrations for 1, 2 or 3 days, after which they were washed three times in sterile distilled water and cultured on shoot proliferation medium. Frequent movement to fresh medium was beneficial to survival. Three successive experiments established the range of concentrations of colchicine, 0.05 mM to 0.25 mM, at which tetraploids were likely to be produced. Thus a protocol for the production of tetraploids was established. Cytometric analysis showed that tetraploid forms of two selections were produced.