| Extreme weather phenomena are more common due to the ongoing global warming,and multiple stress conditions exist concurrently during the growing season of crops,posing a serious threat to global agricultural production and food security as well as raising the bar for crop breeding work.Because the stronger physiological adaptability and greater genetic plasticity,the development and utilization of polyploid as an effective way to cope with the major challenges brought about by environmental changes has been valued by breeders.The method of using colchicine to induce polyploidy is simple to operate and has a high induction rate,and is widely used for the induction of polyploidy.With drought resistance and high water use efficiency,broomcorn millet is known as a pioneer crop in arid areas.The development and use of the broomcorn millet’s genetic resources,however,still lags behind that of the major food crops.In order to offer a reference for the creation and use of broomcorn millet polyploid germplasm resources,colchicine was used to induce broomcorn millet and evaluate broomcorn millet with varied ploidy.Colchicine was used in the study to induce seeds after germination in the broomcorn millet cultivar Shaanmi 1 Agronomic traits,physiology,biochemistry,drought resistance,and transcriptomics of broomcorn millet with different ploidy were compared,and the best treatment concentration and time for broomcorn millet induced by colchicine were summarized.The main conclusions are as follows:(1)Treatment of broomcorn millet seeds after dewy by colchicine,regardless of the concentration of colchicine and the length of treatment time,will have a significant impact on the morphology and survival rate of broomcorn millet seedlings,mainly manifested as the development of germ and radicle slows down,the root system becomes shorter,the germ sheath becomes thicker,and the survival rate decreases,and this phenomenon becomes more and more obvious with the extension of time and the increase of concentration.A comparison of the effects of induction after different treatments showed that although the induction treatment for a short time(2 h)may cause changes in the morphology of seedlings,it cannot successfully induce polyploidy.The induction effect will be impacted by prolonged induction treatment(more than 10 h),which will result in excessive toxicity and basic seedling death.Comprehensive survival rate and induction effect,the induction treatment time of broomcorn millet polyploid was the best at low concentration of 6 h.With medium to high concentrations,the induction treatment time was preferably 4 h.(2)The comparison of agronomic traits,physiological and biochemical indexes and photosynthetic parameters of broomcorn millet with different ploidy showed that the increases of ploidy led to a prolonged growth period in agronomic traits,and dwarfism,increase in the number of branches,decrease in the number of stem nodes,thicken the stem,increase in leaf growth,increase in the leaf area,increase in the total root length,increase in biomass,increase in 1,000 grain weight,and decrease in the panicle length,panicle grain weight and setting rate.In terms of cytology and physiological indicators,the epidermal stomata and guard cells of octaploid broomcorn millet leaf increased significantly,but the number of unit area decreased significantly.The relative water content,antioxidant enzyme activity,soluble sugar and soluble protein content of leaves were higher than those of tetraploid.In terms of photosynthesis-related parameters,octaploid broomcorn millet had higher chlorophyll content,photosynthetic electron transfer rate,potential photochemical efficiency,maximum photochemical efficiency,actual photochemical efficiency,stomatal conductance,intercellular carbon dioxide concentration and net photosynthetic efficiency.(3)Transcriptome sequencing of broomcorn millet genes of different ploidy showed that there was no significant difference in the expression of most genes in different ploidy broomcorn millet,but the expression of about 1691 genes(about 2.46%)changed significantly.The functional analysis of these differently expressed genes showed that these genes were mainly related to chloroplast,endoplasmic reticulum,cell membranes and organelle membranes,regulating the circadian rhythm of broomcorn millet,the synthesis and decomposition of metabolites,the capture of light and carbon fixation in photosynthesis,and the synthesis and metabolism of some sub-biomasses.Therefore,our octuplet broomcorn millet may have higher photosynthetic and metabolic capacity,as well as more nutritious inclusions.(4)The comparison of the relative water content of broomcorn millet leaves of different ploidy broomcorn millet under drought stress preliminarily determined that octaploid broomcorn millet has stronger drought resistance than tetraploid.The analysis of transcriptome sequencing technology showed that there were certain differences in the gene expression patterns and expression of broomcorn millet heterogene under drought stress,among which octaploid and control octeptoid under drought stress had the most differentially expressed genes,while tetraploid under drought stress had fewer differentially expressed genes between the control and the control,GO enrichment analysis showed that octploid broomcorn millet initiated relatively few regulatory pathways under drought stress.Compared with tetraploid,the photosynthesis of octaploid broomcorn millet was not significantly affected under drought stress.KEGG enrichment analysis showed that different regulatory pathways appeared in different ploidy chytes under drought stress,mainly related to starch and sucrose metabolism,linoleic acid metabolism,porphyrin metabolism,β-alanine metabolism,ascorbic acid and aldehyde acid metabolism pathways,which may be the key pathways in which octaploid and tetraploid exhibit different drought resistance.In summary,the main conclusions of the study are as follows : Using colchicine to induce white seeds can obtain polyploidy of broomcorn millet with high efficiency.The best induction treatment is to soak in 0.05 % concentration for 6 h.The abnormal plants were selected as candidate plants at germination stage and seedling stage,and then the ploidy was finally determined by flow cytometry,which was a simple and effective identification method in the identification of broomcorn millet ploidy.There were significant differences in morphology,physiological metabolism and molecular regulation among different ploidy broomcorn millet.Except for the prolongation of growth period and the decrease of fertility,octaploid broomcorn millet was superior to tetraploid broomcorn millet in most traits.And octoploid broomcorn millet has stronger drought resistance than tetraploid,and there are significant differences in the regulation mechanism of drought response.With the development of industry and the change of market demand,polyploid broomcorn millet may have broader utilization space in forage and feed production,saline-alkali land and heavy metal stressed farmland management due to its large nutrition and strong stress resistance. |
