Map- vs. homology-based cloning for the recessive gene ol-2 conferring resistance to tomato powdery mildew |
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Authors: | Stefano Pavan Zheng Zheng Mariya Borisova Petra van den Berg Concetta Lotti Claudio De Giovanni Pim Lindhout Hans de Jong Luigi Ricciardi Richard G. F. Visser Yuling Bai |
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Affiliation: | 1. Laboratory of Plant Breeding, Wageningen University, Droevendaalsesteeg 1, 6708 PB, Wageningen, The Netherlands 2. Department of Agroforestry, Environmental Biology and Chemistry, Section of Genetics and Plant Breeding, University of Bari, Via Amendola 165/A, Bari, 70126, Italy 3. Laboratory of Genetics, Wageningen University, Arboretumlaan 4, 6703 BD, Wageningen, The Netherlands 4. Department of Agro-Environmental Science, Chemistry and Crop Protection, University of Foggia, Via Napoli 25, Foggia, 71100, Italy
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Abstract: | The recessive gene ol-2 confers papilla-associated and race-non-specific resistance to tomato powdery mildew caused by Oidium neolycopersici. In order to facilitate marker assisted selection (MAS) in practical breeding programmes, we identified two simple sequence repeat (SSR) markers and one cleaved amplified polymorphic sequence (CAPS) marker which are linked to the resistance locus and co-dominantly inherited. Aiming to provide a base for ol-2 positional cloning, we used a large segregating F2 population to merge these markers with all the ol-2 linked amplified fragment length polymorphism (AFLP®) markers previously identified in an integrated genetic map. By screening a tomato bacterial artificial chromosome (BAC) library, we detected two BAC clones containing two expressed sequence tags (ESTs) homologous to the gene mlo, responsible for powdery mildew resistance in barley, as well as an ol-2-linked marker. Chromosomal mapping by Fluorescence in situ Hybridization (FISH) revealed major signals of the two BAC DNAs in the pericentromeric heterochromatin of the short arm of chromosome 4, in the same region where the ol-2 gene was previously mapped. The genetic and cytogenetic co-localisation between ol-2 and tomato mlo-homologue(s), in addition to the similarity of ol-2 and mlo resistances for both genetic and phytopathological characteristics, suggests that ol-2 is likely a mlo-homologue. Thus, a homology-based cloning approach could be more suitable than positional cloning for ol-2 isolation. |
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Keywords: | Fluorescence in situ hybridization Homology-based cloning Integrated linkage map Map-based cloning Oidium neolycopersici Solanum lycopersicum |
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