An RFLP map of diploid Hordeum bulbosum L. and comparison with maps of barley (H-vulgare L.) and wheat (Triticum aestivum L.)

This paper describes the first extensive genetic map of Hordeum bulbosum, t he closest wild relative of cultivated barley. H. bulbosum is valuable for haploid production in barley breeding, and because of desirable agronomic c haracteristics, it also has potential for trait introgression into barley. A H. bulbosum map will assist introgression and provide a basis for the ide ntification of QTLs for crossability with barley and other potentially usef ul genes. The present study used a population of 111 individuals from a PB1 xPB 11 cross to develop a genetic linkage map of diploid H. bulbosum (2n=2 x=14) based on barley, wheat and other "anchor" cereal RFLP markers previou sly mapped in other species. Because of the cross-pollinating and highly po lymorphic nature of H. bulbosum, up to four alleles showed segregation at a ny one locus, and five different segregation types were found. This enabled maps to be developed for the PB1 and PB11 parents, as well as a combined m ap. In total, 136 RFLP loci were mapped with a marker coverage of 621 cM. T he markers were generally colinear with barley but H. bulbosum had less rec ombination in the centromeric regions and similar or more in the distal reg ions. Cytological studies on pollen mother cells at metaphase-I showed mark ed distal localization of chiasmata and a frequency consistent with the gen etic map length. This study showed that H. bulbosum was highly polymorphic, making it suitable for trait analysis and supplementing maps of barley.