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Characterization and mapping of QTLS conferring resistance to late blight in potato

by Costanzo, Stefano.

Abstract (Summary)
Field resistance to Phytophthora infestans (Mont.) de Bary, the causal agent of late blight in potatoes, has been genetically characterized by analyzing trait-marker association in a potato diploid segregating family of 230 full-sib progenies derived from a cross between two hybrid Solanum phureja × S. stenotomum clones. Trait data were developed at two locations in Pennsylvania in three replicated field trials between 1999 and 2002. Area under the disease progress curve (AUDPC) was calculated for individual clones in each environment. The distribution of AUDPC values was consistent with the inheritance of a quantitative trait. Relatively high levels of resistance and transgressive segregations were observed within this family. Broad-sense heritability was estimated to be 0.67 with a 95% confidence interval of 0.65-0.78. Since P. infestans can rapidly overcome major race-specific resistance genes, identifying the basis for quantitative resistance is a crucial element for implementing advanced breeding strategies. For this purpose, a genetic linkage map of this population was constructed using previously mapped restriction fragment length polymorphism (RFLP) markers on 132 clones from the same family. A total of 114 RFLP markers have been used and 14 linkage groups, covering approximately 855 cM, have been identified. The total number of loci mapped was 126, and the genome coverage by the map is estimated to be at least 70% with an average distance of 6.8 cM between two markers. Two methods were employed to determine trait-marker association: the non-parametric Kruskal-Wallis test and interval mapping analysis. Analysis of the trait scores combined with the marker segregation data allowed the identification of regions of the genome that were significantly correlated with components of disease resistance. Three major QTLs (quantitative trait loci) were detected on linkage group III, V and XI as a contribution from both parents, explaining 23, 17 and 10%, respectively, of the total phenotypic variation. One additional QTL was detected on linkage group VII with less statistical support. The present study revealed the presence of potentially new genetic loci in the potato genome contributing to general resistance against late blight. These QTLs could represent a specific contribution of the two diploid potato species used in this study. iii
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School:Pennsylvania State University

School Location:USA - Pennsylvania

Source Type:Master's Thesis

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