| Narrow genetic background of cultivated potato (S. tuberosum) is crucial constraint for cultivar improvement, which has been testified by breeding practices all around the world. Fortunately, plenty of primal cultivated species and wild species of potatoes are still existed, which are potential germplasm for cultivar improvement and adopted gradually in potato breeding. As a valuable germplasm highly resistance to late blight, wild species, Solanum demissum, has been being used in potato breeding programs worldwide, by which good results were achieved. S. demissum (2n=72) originated from Mexico. About 200 cultivars related genetically with S. demissum were released worldwide. Except for resistance to late blight, S. demissum also possesses resistances to wart, scab, PVY, PVA, PLRV, and potato beetle, as well as high contents of protein and starch. It has been approved by breeding practices that S. demissum as a female parent can cross easily with cultivated species, and yield components such as more tubers and high specific gravity can be improved by 2~3 times of backcross by its hybrid progenies with cultivated varieties. However, cultivar improvement through crossing with wild species is time-consuming work. How to achieve favorable progresses in relative short time and speed up breeding procedure has been being hotspot attended by breeders.In this thesis, genetic parameters of progeny populations derived from 40 interspecies crosses were analyzed based on three crossing models. The purpose was to explore the effect of improvement of interspecies progeny population, find available methods for eliminating ill characters originated from wild species, and increase breeding efficiency through optimizing procedure of interspecies breeding. The final objective is to speed up breeding course of interspecies hybridization, and to increase efficiency of using wild species in cultivar improvement.The result showed that linkages and interactions of characters between cultivated species and wild species were lessened greatly by means of backcross hybrid population with cultivated varieties. Therefore, there is no any constraint for recombination of characters when S. demissum was used in conventional potato breeding programs.Correlations between some characters were inconsistent in various hybrid populations and backcross populations. The results indicated that correlation coefficients derived from one population cannot be used in others.By means of combining ability analysis, trial result from using the earliness of cultivated varieties to overcome long stolen and late tuberization of interspecific hybrid populations showed that significant variations at 0.01 level were found on mean single tuber weight, marketable tuber rate, length of stolen and variations at 0.05 level were found on yield per hill, tuber number per hill, maturity, specific gravity of tubers, protein content, vitamin content and reducing sugar content in cultivated varieties. Significant variations at 0.01 level were found on number of main stems, stem thickness, marketable tuber rate, and protein content, and significant variation at 0.05 level were found on yield per hill, tuber number per hill, mean tuber weight per hill, length of stolen, maturity, specific gravity and reducing sugar content in interspecific variety populations. Variation of parental interaction effects only was showed on tuber specific gravity significantly. General combining ability (GCA) value of the same character varied greatly among parents, and specific combining ability (SGA) value of the same character was also changeable among cross combinations. The result also showed that the earliness of cultivated varieties can overcome ill characters such as long stolen and late tuberization of wild species.Genetic parameters of first backcross populations derived from various crossing type were analyzed cytogenetically. The results showed that all effects brought by cytoplasm, nucleus, and interaction between cytoplasm and nucleus can be transferred into progenies obviously. Parental cytogenetic effects showed variation significantly in all characters tested. The nucleus effects of the combinations showed variations significantly in 9 characters tested except for plant height, number of main stems, reducing sugar and vitamin C content. Cytogenetic-nucleus interaction effects showed variation at 0.05 level on plant height, stem thickness, yield per hill, and protein content, showed variation at 0.01 level on tuber number per hill, reducing sugar and vitamin C contents. For the same character, effects aroused by cytoplasm and nucleus were varied dramatically among parental lines. Similarly, interaction effects of cytoplasm and nucleus for the same character were also varied greatly. Obvious genetic differences on progenies were found when a parental line used as male or female.Genetic parameters of the second backcross populations were analyzed based on the model of additive-dominant effect and contribution rate analysis. The results indicated that plant height, number of main stems, tuber number per hill, mean tuber weight, stolen length, protein content, reducing sugar content, vitamin C content and eye depth are mainly dominated by gene additive effects, which can be selected in early generations. The ratio of additive variances of maturity and specific gravity of tubers was less than dominant variances, which mean that heterosis would be available for those characters improvement. Contribution rate to phenotypic variances (CRP(C→T)) of marketable tuber rate of all characters tested were different. Except for stem thickness and yield per hill, additive contribution rate on marketable tuber rate (CRA(C→T)) of other 11 characters tested are all significant at 0.01 level, and CRA(C→T)of tuber number per hill, mean tuber weight, specific gravity, protein content, reducing sugar content, vitamin C content, and maturity were all higher than their CRP(C→T). Marketable tuber rate of the second backcross populations can be improved effectively by selecting mean tuber weight and tuber number per hill. Additive contribution rates to marketable tuber rate (CRD(C→T)) of all characters tested were also varied. Crosses selected based on maturity and stem thickness can easily improve marketable tuber rates.According to genetic analysis on backcross populations and application of various improving methods, strategy for accelerating the improving process of interspecific hybrid was made, by which breeding efficiency of interspecific hybridization can be increased. |
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