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| Potato Genome Analysis (Christiane Gebhardt, Research Group ... |
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Group Gebhardt
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Research: Structure and Function of the Potato Genome
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The group’s research activities concentrate on the potato (Solanum tuberosum), which is the worldwide most important crop species of the Solanaceae family comprising more than 3000 species. The potato is most closely related to about 200 tuber-bearing Solanum species native to Mexico, Middle or South America and represents a rich source of biodiversity. Potatoes have with humans in common that both are outcrossing species and that phenotypic and genotypic variation is natural. Unlike humans, the cultivated potato is tetraploid and each heterozygous genotype is fixed by vegetative propagation. Our long-term goals are (1) to elucidate the genetic basis of complex agronomic characters of potato at the molecular level, (2) to contribute to the understanding of structure, function and natural diversity of crop plant genomes and (3) to contribute to the genetic improvement of the cultivated potato by developing molecular diagnostic tools to assist the breeding of new cultivars. To reach our goals, we exploit, as in human genetics, the natural diversity available in the species and its close relatives, and we adapt principles and approaches of human population genetics. Our outputs are: (1) knowledge of genomic positions and identity of genes, which control qualitative or quantitative agronomic characters; (2) DNA-based markers that can be used for marker-assisted selection of superior cultivars; and (3) cloned genes and superior alleles of agronomic characters, which may be transferred into cultivars by genetic engineering.
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Current research areas:
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Late blight of potato caused by the oomycete Phytophthora infestans is the most important disease in potato cultivation. The combination of durable resistance to late blight with good agronomic quality is still a major target of variety development, particularly for production systems that cannot or must not use chemical control. Resistance to late blight can be classified at the phenotypic level as qualitative resistance controlled by single R genes or as quantitative or field resistance controlled by an unknown number of genes. Identification of the genes that control both types of resistance to P. infestans can reveal new strategies and diagnostic markers for molecular breeding. We have cloned R1, the first R gene for late blight resistance and completed several QTL (quantitative trait locus) mapping experiments for quantitative late blight resistance (Ballvora et al. 2002, Bormann et al. 2004). Based on these results, candidate genes for resistance QTL have been identified. Natural variation at candidate loci is now tested for association with quantitative resistance evaluated under field conditions. For genetic material and phenotypic analysis of field resistance to late blight, we collaborate with potato breeding companies. First associations between candidate loci and field resistance to late blight were found (Gebhardt et al. 2004). R1 homologous sequences have been isolated from other S. tuberosum genotypes and other Solanum species and are being characterized for their expression and resistance function.
Damage caused by two root cyst nematode species, Globodera rostochiensis and Globodera pallida, is relevant in middle European potato cultivation. Genetic dissection has previously shown that resistance to these nematodes is controlled by R genes and/or by major QTL. Recently, we cloned the Gro1-4 gene for resistance to G. rostochiensis based on a candidate gene approach (Paal et al. 2004). The Gro1-4 gene is one member of a gene family, which we further characterize for gene specific expression and function. Diagnostic PCR markers for resistance to G. pallida were developed that are being evaluated in collaboration with potato breeders for general applicability in marker-assisted selection.
Tuber yield, tuber starch content and tuber sugar content are complex quality traits, which are all functionally connected with carbohydrate metabolism. The genes and biochemical pathways for synthesis, degradation and transport of carbohydrates are among the best studied in plants. Therefore, QTL (quantitative trait loci) for tuber starch and sugar content are a model system for testing the candidate gene approach to identify genes that control complex agronomic traits. QTL for tuber starch and sugar content (cold-sweetening) have been mapped previously using molecular markers, as well as genes functional in carbohydrate metabolism and transport (Schäfer-Pregl et al. 1998, Chen et al.2001, Menendez et al. 2002) . A number of positional candidate genes were identified. These candidate genes are now studied for natural variation associated with tuber quality traits in tetraploid potato breeding populations (Li et al. 2005).
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© 2011, Max Planck Institute for Plant Breeding Research, Cologne |
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