| Medicago sativa L. cv. Qingshui belong to the rhizomatous Leguminous forage,and turn green early. They have fast growth, a mass of developed root, increased branch, high tolerance, and good resistance to trample. But in the meantime, they have many disadvantages, such as smaller plants and blades, higher fiber. The research chooses different colchicines to induce the gemmiferous seed, its radicle and the growth cone of stem tip of Qingshui alfalfa, the aim is to select the best processing organization and method by comparing mutation rate and survival rate. Then identified the variant from morphology, chromosome ploidy and cytology under the treatment. At the same time, evaluate the drought resistance, biomass and quality of variant plant, the purpose is to get more new alfalfa materials who have many bigger leaf, higher biomass and protein, and lower fiber. In this paper, the results of the study are as follows:1. When colchicines deal with the gemmiferous seeds, its radical and growth cone of stem tip, the optimum concentration is 0.1%, and the mutation rate are 28.84%, 35.49%, 20.06%; When deal with the gemmiferous seeds and its radical, the best processing time is 8h, the mutation rate are 27.43% and 31.71%. While the best time is 12 h when processing the growth cone of stem tip, and the mutation rate is 19.15%. When deal with the gemmiferous seeds and its radical, the best processing combination is 0.1%+8h, and the mutation rate are 35.73% and 41.84%, while the best processing combination is 0.1%+12h when deal with the growth cone of stem tip, the mutation is 21.00%.Therefore, it’s the best mutation method to dispose the radicle when using processing combination of 0.1%+8h.2. The plant height, seedling length and root length of mutant seedlings have different degree increase than concrast with the processing of colchicines, and in 0.1% the change most significantly(P<0.05)are 5.81%, 5.74% and 5.81%. The increase are 4.49%, 4.63%, 4.49% and most significantly(P<0.05) than control when processing 8h. And the increase are 9.32%, 8.18%, 9.32% and most significantly than contrast as well in 0.1% colchicine solution for 8h. So the plant height, shoot and root length of variation seedling increased most obviously than contrast in the treatment of 0.1%+8h.3. In different concentrations, different times and different combination of concentration and time, the leaf area, thickness, number and stem diameter of variant seedlings increased. The leaf area and stem diameter have maximum 91.61mm2 and 1.14 mm under concentration of 0.2%; The maximum of leaf thickness and euphylla number are 1.20 mm and 53.63 piece under concentration of 0.1%. The maximum of leaf area, thickness and stem diameter were 90.00 mm2, 1.19 mm and 1.09 mm when processing 12 h, while the maximum of euphylla number is 52.5 piece in 8h. The leaf area, thickness, euphylla number and stem diameter all increased in different degree under the processing combination of colchicines, and the maximum of them are 94.63 mm2, 1.242 mm, 57.7piece and 1.17 mm in 0.1% colchicine solution for 8h. So the leaves and stem diameter of variant seedlings changed most obvious than contrast in the treatment of 0.1%+8h.4. Colchicine treatment can make the tip cell chromosome of alfalfa radicle root mutate, and produce a variety of mutant type(4x<2n<8x, 2n=8x, 2n>8x type). If use the proportion of 2n=8x(octaploid) cell as the double rate, in different colchicine concentrations, the biggest proportion of 2n=8x cell is 10.89% in 0.1%; In different colchicine times, the biggest proportion of 2n=8x cell is 9.78% in 8h; In different treatment the biggest proportion of 2n=8x cell is 13.33% in 0.1%+8h. So the effect is more obviously in colchicine treatment, it is largest in the treatment of 0.1%+8h.5. In different concentrations, different times and different combination of concentration and time, the leaf epidermal cells have changed in different degree, the stoma density reduced relatively, the guard cell size and the chloroplast number increased relatively. Under the combination of 0.1%+8h,the minimum of stoma density is 9.74A/mm2, the maximum of guard cell size and chloroplast number are 34.04um×27.05um(length×width), 1.27(length/width) and 24.50.6. Under the processing of colchicines, the first cutting, the second cutting and the total fresh and total hay biomass of variant seedlings have increased more obviously(P﹤0.05) than contrast in the treatment of 0.1%+8h and 0.2%+4h. The CP content and RFV value of variant seedlings increased more obvious than contrast; however the ADF and NDF content decreased more obviously than contrast. So the processing materials of alfalfa are more excellent than others in the treatment combinations of 0.05%+8h and 0.2%+4h, they have high biomass, CP and RFV, at the same time, in 0.1%+8h the processing materials are good as well.7. Under the processing of colchicines, the leaf RWC, the Pro content and the chlorophyll content of variant seedlings increased compared to the contrast; Meanwhile, leaf MAD accumulation lower than contrast. The higher drought resistance intensity sequence of seedling than contrast based on each index comprehensive evaluation is: 0.1%+4h>0.2%+12h>0.2%+8h>CK. So the drought resistance is comparatively high in the the treatment of 0.1%+4h and 0.2%+12h. |
