Polyploid induction for breeding in Agapanthus L’Héritier and Dianthus L.

Abstract

An investigation of polyploid induction in two plant genera was conducted. The purpose in Agapanthus was to produce sterile triploids in the F1 generation as a means to reduce the invasiveness of this plant. For Dianthus the polyploidisation of two yellow-flowered diploid species would provide a bridge to enable crossing with the hexaploid garden pink D. plumarius, to introduce yellow-coloured flowers into the range of garden pinks. For each of the diploid species, a doubling of their genomes to produce tetraploids was required. The tetraploids were then to be back-crossed to the diploid progenitors, producing triploid plants. For Agapanthus that was the goal. Dianthus required a further doubling of the triploid genome to create fertile hexaploids, which would enable them to be hybridised with the garden pink. Seedlings of Agapanthus and Dianthus were treated with either colchicine or oryzalin at predetermined concentrations and treatment times. Distinctive phenotypic appearance was used as the basis for selecting survivors for polyploid assessment. Guard cell lengths and their chloroplast numbers in the epidermis were measured. Chromosome numbers in root tips (Agapanthus) and shoot tips (Dianthus) were examined. Flow cytometry was then used to confirm the polyploid status. Colchicine treatment produced 50% mortality in Agapanthus seedlings, but oryzalin was more toxic, leaving only 12.5% surviving. No entire tetraploids were created, but diploidtetraploid chimeras were found in 10% (colchicine) and 5% (oryzalin) of the surviving treated plants. In contrast, mortality in Dianthus knappii with colchicine treatment was 5% and polyploid formation was 14%, including one entire tetraploid. Oryzalin caused 11% mortality in D. knappii, and 44% in D. basuticus. Chimeric polyploids were evident in 22% of D. basuticus, but only 1.7% were found in D. knappii treated with oryzalin. The successful induction of polyploids depends on choice of agent, its concentration, and the duration of treatment. Clear differences in each species response were apparent, even between species of the same genus. Research into these aspects is ongoing.