| As one of the main staple crops in China, potato is playing more and more important role in agriculture production. Clear breeding objectives need to be established in order to meet the requirements of potato industry and demanding of market. Varieties approved in China have contributed not only to potato production but also to be genetic resourse in varietial improvement. In this thesis, genetic diversity of approved potato varities in China was studied by pedigree analysis, phenotypic traits identification and SSR markers. The main conclusions are as follows:1. Genetic relationship between 288 potato cultivars authorized in China were analysed by documentary study. The results indicated: (1) 93 cultivars released before 1983 were shown a narrow genetic background, 60 of 93 varieties were the progenies of 'Duozibai'; (2) It was the downturn since 31 cultivars were bred during 1983 to 1990; (3) Diverse germplasm were introduced in breeding as parents during 1991 and 2000, while many released varieties were used for parents to develop new cultivars; (4) More and more exotic germplasm has been integrated into breeding program so that genetic background has been broaden since 2001 while 94 cultivars has been released. (5) The cultivars's genetic diversity at four stages by SSR makers was given the same results as pedigree analysis.2. As breeding parents, exotic cultivars greatly contributed to gene pool in potato breeding. Of 235 cultivars, 34.7% with 100 cultivars were derived from USA stocks, 33.3% with 93 cultivars were from German, 20.8% with 58 cultivars were from Polish, 21.5% with 63 cultivars were from Canadian, Dutch and CIP's.3. UPGMA cluster analysis based on 20 phenotypic traits showed that 185 cultivars could be classified into two clusters when D=12.5. And the second cluster could be grouped into two sub-clusters when D=11.5. All 185 cultivars were classified into 11 groups when D=10.0. The group 6 was the biggest one including 90 cultivars.4. 12 SSR primers were employed to study genetic diversity of 203 cultivars. They produced amplified fragments with a total of 125 putative alleles, in an average of 10.4 alleles per marker and ranged from 5 to 18. Genetic distance between 203 cultivars varied from 0.22 to 0.72 with an average of 0.62.5. UPGMA cluster analysis based on SSR markers showed that 203 cultivars were classified into two groups of wild and potato cultivars when GS =0.47; All cultivars were grouped into 15 clusters when GS =0.7. Most cultivars with close genetic relationship were grouped into same clusters and the first cluster included 91 cultivars. |
