Studies On Genetic Diversity Of Citrus Resource In Hunan And Characters Of Nutrition, Photosynthesis

There is a plentiful germplasm resources in Hunan. The wild species and ancient cultivar species of Poncirus Raf., Citrus L.Fortunella Swingle were discovered by investigation and sorting out. The discovery of C. ichangensis Swingle. Daoxian wild tangerine. Mangshan wild mandarin. F.hindsii(champ.)Swingle. etc. has been laid down a material basis for Hunan as being one of citrus native centers in the world.The geographical distribution of the wild citrus resources in Hunan Province has two distinct lines of demarcation. One is the demarcation line between the north and the south, which lies roughly in latitude 26°N.To the south of this line. It is the Nanling Mountains. We believe that the Nanling Mountain in China must be one of the native centers of subgenus Eucitrus. The other is demarcation line between the east and the west, which situated roughly longitude 113°E. To the east of this line are the hilly areas in the south east part of China. Here, the wild resources of Fortunella are very abundant. The C. ichangensis Swingle of subgenus Papeda is widely distributed in the hilly area in the west part of Hunan.From the view-point of geographical distribution, It is proposed that the evolution of the wild resources of citrus seem to have gone through such a process that the wild species of loose-skin mandarin growing in the hilly areas of the south China have evolved from the wild C. ichangensis Swingle growing in the southwest plateaus of China. And the Fortunella growing in the southeast part of China has evolved from wild mandarin. The discovery of Mangshan wild mandarin supplied the sample for the classification between Gan and Ju.The pollen exine ultrastructure of several citrus plants was examined by using ultrathinned sectioning technique under transmission electron microscope. Results showed that the pollen grains of the citrus have 4~5 colporates, thicker endoexine. The pollen exine ultrastructure is different from each other, which specifies the genetic diversification of citrus. The pollen exine of wild citrus possesses granular bacules, and that of cultivated citrus possesses columellate. It may be concluded that the developed tendency of the pollen exine of citrus goes from the granular bacule to...