In vitro induction of polyploidy by colchicine treatment of shoots and preliminary characterisation of induced polyploids in two Miscanthus species

Grasses from the genus Miscanthus are becoming a key renewable raw material for energy production. The aim of this study was to find a suitable treatment combination that would effectively induce polyploids using in vitro shoots propagated from Miscanthus grass species. The experiments had a three-factorial arrangement (genotype, colchicine concentration, exposure time). In this study, combinations of four colchicine concentrations (156.5, 313, 626 and 1252 μM) and three exposure times (6, 18 and 24 h) were tested in diploid and triploid genotypes belonging to M. sinensis and M. x giganteus. A total of 448 polyploids, as assessed by flow cytometry of regenerates, were obtained for all experiments. The efficiency of polyploidisation in one of the tested genotypes reached 55% after 18 h of treatment with 313 μM colchicine. Regardless of the genotype tested, the treatment with 313 μM colchicine for 18 h seemed to be the most effective combination (14.9%) for generating polyploidy and, together with the 6 h treatment with 313 μM colchicine, was optimal for shoot survival. Stomatal length and pollen grain diameter were identified as suitable parameters for the identification of putative Miscanthus polyploids. The beneficial impact of increased ploidy on agronomic traits was genotype-dependent. In four out of five genotypes tested, the stem diameter significantly increased in colchicine-induced polyploids compared to corresponding controls. The tetraploid forms of two genotypes were found to have significantly greater values of tuft weight (dry matter), significantly greater stem diameter and, in the case of one genotype, even significantly taller stems when compared with controls. Thus, they might be valuable materials in breeding efforts to create high-yielding Miscanthus forms.