Analysis Of Genetic Diversity Of Sweetpotato Germplasm In China And Improvement Of High Starch Sweetpotato Population By Recurrent Selection

"Sweet potato is the health and energy plants of human in 21st century." To develop new good-quality, high-yielding, resistance and specialized type varieties is the main aim of breeders at anytime. Moreover, exploration, innovation and utilization of the sweet potato germplasm resources are the basis of gained new breakthrough sweet potato varieties. Therefore, the agronomic traits, the integrated index of agronomic and morphological traits and the RAPD markers were used for genetic diversity of the Chinese sweet potato cuurent germplasm. This study was to use recurrent selection in population improvement of high starch sweet potato in China. The results showed the there were obvious effect of recurrent selection method on agronomic traits population improvement effect. At the same time, foundation populations were compared to recurrent selection population in genetic diversity with RAPD markers. The main results were as following:1. Genetic diversity of Chinese sweet potato germplasm resources.(1) Genetic diversity analysis of 36 germplasm resources based on agronomic traits showed that the introduction resources existed a longest vine leaves, the largest fresh weight of relativity, standard deviation and coefficient of variation and the smallest drying rate and the rate of starch, stem diameter of relativity, the small standard deviation, coefficient of variation, which suggest that they have abundant genetic diversity. Wide planting varieties of important agronomic traits such as a long, the number of branches, leaves and vine stem heavy differential, standard deviation, the coefficient of variation was less than both the domestic and the introduction resources. As far as agronomic traits (especially with a long, vine leaves and fresh weight of the genetic diversity) are concerned, the genetic diversity of the introduced resources was significantly higher than that of domestic germplasm. Therefore, the introduced resources will play a very important role in sweet potato breeding. (2) Genetic diversity analysis based on RAPD analysis:Twenty out of 50 stripes of RAPD primers that can produce polymorphic, clear and bright bands, with reliable repeatability, have been used for DNA amplification of 36 genotypes. The results showed that total 177 bands were amplified in these materials and 172 bands were polymorphic among them. The polymorphism frequency was up to 97.18%. Each primer amplified 4～15 polymorphic bands, with an average of 8.7. It was obvious that there were abundant diversity in the 36 materials on the DNA level.(3) The cluster dendrogram from the agronomic traits was not consistent with the pedigree of the materials, while the cluster dendrogram based on RAPD markers was not consistent with it. The cluster dendrogram based on the integrated index was also consistent with the pedigree and the cluster dendrogram based on RAPD markers. The results showed that it was reliable to utilize RAPD markers for assisted selection in sweet potato breeding.(4) The results derived from agronomic traits and integrated index showed the largest genetic distance was in introduced resources, and the next was in domestic resources, while the smallest was in main planting varieties. Moreover, the largest average genetic distance was between introduced resources and domestic resources, and the second between introduced resources and main planting varieties, while the smallest between domestic resources and main planting varieties. RAPD analysis showed that the largest genetic diversity exists within in main planting varieties, and the next within introduced resources, while the smallest in domestic resources. Moreover, the largest genetic difference existed within types was between main planting varieties and introduced resources, and the next between main planting varieties and domestic resources, while the smallest between domestic resources and introduced resources.(5) The results showed that the average genetic distances, based on the RAPD markers with the genotypes including H11-67, chuanshu 294, mianfen 1, mainshuzaoqiu, chuanshu 27 and zhapyuan 16 in domestic resources, fengshoubai, chaoshu 1 and yushu 7 in main planting resources, and tainong 27, neiyuan, and aozhouhuang in introduced resources, were larger than their main parents. Among them, H11-67 was with half blood of the wild species, and was large difference from other resources. This showed that it was significant to further strengthen the study and utilization of the wild relatives resources to broaden the genetic basis in the sweet potato breeding.2 Improvement effect and genetic diversity analysis of the high starch sweet potato recurrent selection populations (1) To determine basic principles and methods of the construction of high starch sweet potato basic populations and the recurrent selection, it commenced from the construction of basic parents populations, centered the recurrent selection, and aimed at improving innovation germplasm resources and identification of high sweet potato starch based groups and the construction of recurrent selection of the basic principles and breeding good-quality, high-yielding, resistance and specialized varieties. The basic populations of excellent genes, high mean, and rich genetic variation high starch sweet potato varieties or lines had been constructed, with artificial mixture pollination or group hybridizing, recurrent selection to break the linked negative gene, enhance favorable gene recombination frequency and create new breakthrough quality traits.(2) During recurrent selecting, the first selection population (C₁) had the reduced agronomic traits compared with the basic population. After the second selecting, the agronomic traits especially the weight of dried potato and fresh potato of the population (C₂) were infinitely improved compared with C₁. The change tendency of quality traits such as the drying rate and starch rate were different from others. Results of selection showed that after a slightly degradation of C₁, C₂ had the improvement but they had not reached the level of C₀. Although it is rather difficult to enhance the drying rate and starch rate in a short period, the genetic correlation coefficient between the drying and starch rate and the dry weight per plant was changed from the strong negative correlation to the weak negative or positive correlation with recurrent selecting.(3) Along with the increase of selection times, fresh weight and dry weight per plant were significantly improved with the slightly lowered variation coefficient, and there was the small variation in drying and starch rate.(4) RAPD analysis results showed that the genetic difference within populations reduced after the first selection and it was saliently increased after the second selection. Cluster analyses showed that RAPD markers could accurately response and determine the genetic variations and the pedigree relations. The result further indicated that RAPD markers are reasonable and reliable markers in assisted selection breeding of sweet potato.