PHYSICAL MAPPING AND CLONING OF A TRANSLOCATION IN SUGAR-BEET (BETA-VULGARIS L) CARRYING A GENE FOR NEMATODE (HETERODERA-SCHACHTII) RESISTANCE FROM BETA-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 w ere investigated. Short interspersed repetitive DNA elements exclusive ly hybridizing with wild beet DNA were found to be dispersed around th e translocations. The banding pattern as revealed by genomic Southern hybridization was highly conserved among translocation lines of differ ent origins indicating that the translocations are not affected by rec ombination events with sugar beet chromosomes. Physical mapping reveal ed that the entire translocation is represented by a single SalI fragm ent 300 kb in size. A representative YAC (yeast artifical chromosome) library consisting of approximately 13,000 recombinant clones (2.2 gen ome equivalents) with insert sizes ranging between 50 and 450 kb and a n average of 130 kb has been constructed from the resistant line A9060 01. Three recombinant YACs were isolated from this library using the w ild beet-specific repetitive elements as probes for screening. Colinea rity between YAC inserts and donor DNA was confirmed by DNA fingerprin ting utilizing these repetitive probes. The YACs were arranged into tw o contigs with a total size of 215 kb; these represent a minimum of 72 % of the translocation.