Confirmation of repulsion molecular markers linked to rhizomania resistance gene (Rz1) and evaluation of gene dose effect in sugar beet genotypes

Rhizomania is the most important disease of sugar beet in Iran and some other parts of the world, and plays an essential role in decreasing sugar yield in fields. The best approach to control this disease is to use resistant varieties. Tagging the resistance genes in breeding programs, by molecular markers is necessary. In this study, some breeding populations and commercial varieties of sugar beet originated from Rz1 resistance source were used for validation and repeatability of 6 repulsion molecular markers. Accordingly, ELISA data related to greenhouse evaluation of rhizomania resistance were used in some breeding populations. For molecular analysis, DNA was extracted from leaf samples and RAPD-PCR was performed by using the primers related to the markers of interest. The RAPD-PCR products were separated by gel electrophoresis, After electrophoresis, was stained with ethidium bromide and was observed using gel documentation device and finally was scored for the presence or absence of marker bands. In next step, conformation of the markers with ELISA data in single plants were measured in breeding populations and the precent presence of the markers in commercial varieties was determined. Comparison between ELISA and molecular analysis results showed that repulsion markers (the markers linked to the susceptibility allele) PN3 and PN7-2 had acceptable agreement with ELISA (92% and 98% respectively), susceptible varieties (87% and 90% respectively), and resistant varieties (75% and 97% respectively). Also, the results of the gene dose effect showed that the average OD value of ELISA of the dominant homozygote plants (Rz1Rz1) was significantly lower than the heterozygote plant (Rz1rz1) in the repulsion markers.