DNA MARKERS CLOSELY LINKED TO NEMATODE RESISTANCE GENES IN SUGAR-BEET(BETA-VULGARIS L) MAPPED USING CHROMOSOME ADDITIONS AND TRANSLOCATIONS ORIGINATING FROM WILD BEETS OF THE PROCUMBENTES SECTION

Genes conferring resistance to the beet cyst nematode (Heterodera scha chtii Schm.) have been transferred to sugar beet (Beta vulgaris L.) fr om three wild species of the Procumbentes section using monosomic addi tion and translocation lines, because no meiotic recombination occurs between chromosomes of cultured and wild species. In the course of a p roject to isolate the nematode resistance genes by strategies of rever se genetics, probes were cloned from DNA of a fragmented B. procumbens chromosome carrying a resistance gene, which had been isolated by pul sed-field gel electrophoresis. One probe (pRK643) hybridized with a sh ort dispersed repetitive DNA element, which was found only in wild bee ts, and thus may be used as a molecular marker for nematode resistance to progenies of monosomic addition lines segregating resistant and su sceptible individuals. Additional probes for the resistance gene regio n were obtained with a polymerase chain reaction (PCR)-based strategy using repetitive primers to amplify DNA located between repetitive ele ments. One of these probes established the existence of at least six d ifferent chromosomes from wild beet species, each conferring resistanc e independently of the others. A strict correlation between the length of the wild beet chromatin introduced in fragment addition and transl ocation lines and the repeat copy number has been used physically to m ap the region conferring resistance to a chromosome segment of 0.5-3 M b.