Colchicine-induced tetraploidy influences morphological and cytological characteristics and enhances accumulation of anthocyanins in a red-fleshed radish (Raphanus sativus L.)

Red-fleshed radishes (RFRs) are economically important root vegetable in the Brassicaceae family that contain high concentrations of radish-red pigment in their fleshy root. However, the yield of the fleshy root is limited and germplasm resources for radish improvement are lacking. Genome doubling is an effective and efficient breeding tool for the rapid creation of new germplasm resources. Therefore, we aimed to induce tetraploidy in RFRs to improve pigment production. RFR seeds were immersed in aqueous colchicine (0, 0.01, 0.05, 0.10, 0.15, and 0.20% (w/v)) for 24 h followed by cultivation at 25℃ for 7 days, and those with uniform and distinctly swelled and short hypocotyls were selected as putative tetraploids. The putative tetraploids were identified by flow cytometry, and then we further examined the morphological and cytological characteristics of the diploid and tetraploid plants and measured gene expression via reverse transcription quantitative PCR. The results indicated that the most suitable concentration of colchicine (0.05% (w/v)) could induce tetraploidy in RFRs, with a tetraploid-induction rate as high as 34.50%. In addition, tetraploids exhibited a “gigantism” effect in both morphological and cytological traits, including swelled hypocotyls, thicker cotyledons, larger stoma, wider and longer leaves, taller plants, larger flowers, increased pollen size, larger seed pods and seeds, and a larger taproot. Moreover, compared with diploid plants, the pigment content and yield of pigment per plant of tetraploid plants were increased by 65.11% and 216.82%, respectively. Therefore, we present a simple and efficient method for tetraploid induction via soaking radish seeds in 0.05% (w/v) colchicine for 24 h. The results showed that tetraploid plants not only exhibited obvious “gigantism” effects but also significantly enhanced accumulation of anthocyanins, and represent a practical breeding material for improving pigment yield in RFRs.