Morphological, anatomical, physiological, and cytological studies in diploid and tetraploid plants of Plantago psyllium

Plantago psylliumis is under development as the source of mucilage, but has not been entirely domesticated. Since mucilage content is low and variable in the medicinal plant, it is imperative to apply breeding approaches to accelerate the domestication process and improve the mucilage content in the seeds. One approach to achieve these purposes is polyploidy induction, which can increase the size of plants and their phyto-medicines. To conduct this approach and evaluate the effect of in vitro-induced polyploidy on different traits of P. psylliumis, a gradient of colchicine concentrations, 0.1, 0.3 and 0.5% (w/v), was used to treat the terminal buds for 6, 12 and 24 h. The terminal buds were separately treated with different trifluralin concentrations, 7.5, 15 and 22.5% (w/v), for 12, 24 and 48 h. The optimal treatments of 0.5% colchicine for 24 h, and of 22.5% (w/v) trifluralin for 72 h resulted in an induction efficiency of 23% and 19%, respectively. Chromosome counting revealed successful chromosome duplication in tetraploids (2n = 4x = 24), in contrast with intact diploids (2n = 2x = 12). Duplication of DNA size in tetraploids was also proved by flow-cytometry analysis. The tetraploids size was larger than their intact diploids for spike, seed and pollen grain, leaf thickness, and plant height. The stomata of tetraploids were larger with lower density than diploids. The chloroplast number in guard cells, along with chlorophyll and carotenoid content all were higher in tetraploids. In final, our study suggests that tetraploidization could be useful to improving the seed mucilage content for commercial use. Key message We firstly fulfilled the in vitro induced tetraploidy in P. psyllium by 0.5% colchicine for 24 h and 22.5% (w/v) trifluralin for 72 h, and improved the mucilage content in the seeds.