Studies On Morphological Characteristics And Freezing Tolerance Of Dwarfed Citrus Medica L. Var. Sarcodactylis Swingle And The ISSR And SSR Analysis

Citrus medica L. var. sarcodactylis Swingle (finger citron) is a variation of Citrus medica L. which belongs to Citrus of Rutaceae. At present, finger citrons are mainly cultivated in Guang Dong, Guang Xi, Si Chuan, Zhe Jiang, Jiang Xi, Fu Jian and Yun Nan. The fruits produced in Jin Hua, Zhe Jiang are most famous, and are named "golden finger citron". But the plants are weak in freezing tolerance. In another hand, the green peel finger citrons which are most widely cultivated in Jin Hua have some disadvantages as potted plants, such as big, many thorns, big crown size and branches drooping because of the big heavy fruits. In order to increase the value of golden finger citron, it's necessary to breed species which are not only dwarfed but also can resist cold. We bred a new strain of finger citron induced by radiation. This promising strain had typical dwarfed characters and was suitable to be potted.Firstly, the morphological characteristics of dwarfed finger citrons induced by ¹³⁷Cs-γradiation were compared with the green peel finger citrons, including crown size, node length, thorn amount, length of new shoots, circumference of new treetops, arborizations, length, width, thick- ness and area of the leaves and size of the fruits. The results indicated that the dwarfed finger citrons had some typical characters such as smaller crown size, shorter node length, less thorns, smaller and thicker leaves and smaller fruits. These characters provided much convenience to spread it in miniascape.Secondly, we studied the changes of physiological indexes of the two types under the temperature 4℃, 0℃and -4℃. We measured the changes of the content of soluble sugar, malonaldehyde (MDA) and free proline, the activity of superoxide dismutase (SOD) and the relative electronic conductivity. The results showed that under 4℃the dwarfed finger citrons were liable to be injured, based on the indexes of relative electronic conductivity and SOD. Under -4℃the green peel finger citrons were liable to be injured based on the index of MDA. However based on the index of the content of soluble sugar, the dwarfed finger citrons were less freezing tolerance. The content of free proline had no significant change. Integrating the results, we drew a conclusion that the dwarfed finger citrons were not better than green peel finger citron on frost-resistance.Genetic background of different finger citrons and their relatives was assayed by ISSR and SSR markers to confirm whether the dwarfed finger citrons had genetic stability. The ISSR products were detected with 2% agarose gel electrophoresis. The results indicated that the dwarfed fi- nger citrons were closest to green peel finger citrons and the similarity coefficient was 0.9677. The SSR products were detected with 8% denaturing polyacrylamide gel electrophoresis. The results indicated that the dwarfed finger citrons were closest to white peel finger citrons and the similarity coefficient was 0.9524. The results of these two markers had some difference. Based on the fact that the dwarfed finger citrons were induced by ¹³⁷Cs-γradiation from green peel finger citrons, we considered that the ISSR marker was more suitable for the genetic background research of the finger citrons. Perhaps, the difference of SSR from ISSR was because of the small amount of SSR primers. Based on the results of ISSR and SSR markers, we considered that the dwarfed finger citron induced by ¹³⁷Cs-γradiation from green peel finger citron had genetic stability. The dwarfed characters were not caused by cultivation and environment.In conclusion, this study identified that the finger citrons induced by ¹³⁷Cs-γradiation had obvious dwarfed characters and these dwarfed characters can inherit stably. However, this dwarfed finger citrons were not better than green peel finger citrons on frost-resistance. Our study will contribute to the spread of dwarfed finger citrons as potted plants.