POTENTIAL AND LIMITATIONS OF ISOZYMES FOR CHROMOSOMAL LOCALIZATION OFRESISTANCE GENES AGAINST BARLEY MILD MOSAIC-VIRUS (BAMMV)

To assess the possibilities offered by isozymes to locate resistance g enes against barley mild mosaic virus (BaMMV), the isozyme patterns of 19 barley (Hordeum vulgare L.) genotypes carrying genes different fro m ym4 were determined. Of the 15 isozyme systems tested, only three we re polymorphic, namely aconitate hydratase, esterase, phosphogluconate dehydrogenase, providing markers on four of the seven barley chromoso mes. Studies of F-2 progenies derived from three crosses between resis tant genotypes and susceptible varieties failed to reveal linkage betw een resistance genes and isozymes. Another goal of the experiment was to study the linkage relationships between ym4 and the esterase locus (Est1-Est2-Est4). Our estimates of the recombination rate between thes e two loci (3.41 acid 8.32%) were in the range of those reported betwe en these esterases and one of the resistance genes of the Chinese vari ety Mokusekko 3.