Physical mapping and cloning of a translocation in sugar beet (Beta vulgaris L) carrying a gene for nematode (Heterodera schachtii) resistance from B. procumbens

Two diploid (2n=18) sugar beet (Beta vulgaris L.) lines which carry monogenic traits for nematode (Heterodera schachtii Schm.) resistance located on translocations from the wild beet species Beta procumbens were investigated. Short interspersed repetitive DNA elements exclusively hybridizing with wild beet DNA were found to be dispersed around the translocations. The banding pattern as revealed by genomic Southern hybridization was highly conserved among translocation lines of different origins indicating that the translocations are not affected by recombination events with sugar beet chromosomes. Physical mapping revealed that the entire translocation is represented by a single Sal I fragment 300 kb in size. A representative YAC (yeast artifical chromosome) library consisting of approximately 13,000 recombinant clones (2.2 genome equivalents) with insert sizes ranging between 50 and 450 kb and an average of 130kb has been constructed from the resistant line A906001. Three recombinant YACs were isolated from this library using the wild beet-specific repetitive elements as probes for screening. Colinearity between YAC inserts and donor DNA was confirmed by DNA fingerprinting utilizing these repetitive probes. The YACs were arranged into two contigs with a total size of 215 kb; these represent a minimum of 72% of the translocation.