In vitro polyploid induction in Allium grayi Regel using colchicine

Allium grayi Regel is a seasonally limited small perennial herb of the subfamily Allioideae, and is endemic to Matsu, Taiwan. The species possesses nutritious, ornamental value, and biological pharmacological activity. This study evaluated for the first time to induce polyploidy using the dissected bulb of A. grayi as explants in vitro, with the expectation of increasing the bulb size. Sterile bulbs were divided into four equal parts and pre-cultured under different durations before being soaked in a one g/L colchicine solution for 12 or 24 hours. Survival, regeneration, variation, and tetraploid induction rates were recorded, while ploidy levels were determined by flow cytometry and stomatal traits were measured microscopically. The results showed that pre-cultured treatment after dissecting the sterile bulbs increased the variation rate of the plants, with the group that was left static for 10 days before immersing in a one g/L colchicine liquid medium for 24 hours showing the best results. The variation rate reached 100%, and the induction rate of tetraploid plants reached 20% by flow cytometry examination. Among 123 regenerated shoots, 13 were chimeras and three stable tetraploid lines were established, all exhibiting larger stomata and lower stomatal density than diploids. These tetraploid lines provide great potential for future breeding and improvement of Matsu native shallot cultivars.