MOLECULAR MARKER ANALYSES OF POWDERY MILDEW RESISTANCE IN BARLEY

Powdery mildew, caused by Eryisphe graminis f. sp. hordei, is one of t he most important diseases of barley (Hordeum vulgare). A number of lo ci conditioning resistance to this disease have been reported previous ly. The objective of this study was to use molecular markers to identi fy chromosomal regions containing genes for powdery mildew resistance and to estimate the resistance effect of each locus. A set of 28 F-1 h ybrids and eight parental lines from a barley diallel study was inocul ated with each of five isolates of E. graminis. The parents were surve yed for restriction fragment length polymorphisms (RFLPs) at 84 marker loci that cover about 1100 cM of the barley genome. The RFLP genotype s of the F(1)s were deduced from those of the parents. A total of 27 l oci, distributed on six of the seven barley chromosomes, detected sign ificant resistance effects to at least one of the five isolates. Almos t all the chromosomal regions previously reported to carry genes for p owdery mildew resistance were detected, plus the possible existence of 1 additional locus on chromosome 7. The analysis indicated that addit ive genetic effects are the most important component in conditioning p owdery mildew resistance. However, there is also a considerable amount of dominance effects at most loci, and even overdominance is likely t o be present at a number of loci. These results suggest that quantitat ive differences are likely to exist among alleles even at loci which a re considered to carry major genes for resistance, and minor effects m ay be prevalent in cultivars that are not known to carry major genes f or resistance.