Linked inheritance of the microsatellite locus ORS 822 with the gene Plarg controlling the resistance to downy mildew in sunflower

Resistance to the downy mildew pathogen Plasmopara halstedii (Farl.) Berlese et de Toni in sunflower is controlled by the resistance gene Pl. The Plarg gene is currently promising in breeding for resistance as it is effective against all known races of the pathogen. This gene is introgressed from the wild species Helianthus argophyllus. Molecular markers and, in particular, simple microsatellite repeats (SSRs) allow to control the transfer and pyramiding of disease resistance genes. However, validation of the molecular marker is needed to prove its reliability. The microsatellite marker ORS 822 was tested to identify the Plarg gene. We conducted the research on a hybrid combination of a susceptible sunflower line of VNIIMK's breeding VK 925 and a resistant line RHA 419, a donor of the Plarg gene. We es-tablished that these lines differ from each other by the allelic state of this locus. Molecular analysis of the F1 generation showed that the microsatellite locus is inherited codominantly. We obtained the F2 generation by self-pollination and made a phytopathological evaluation of resistance to P. halstedii. Split analysis by ph-notype showed that the actually observed segregation corresponded to the theoretically expected 3:1 model for monogenic inheritance of the trait. Based on the obtained data, we determined that the Plarg gene and microsatellite locus ORS 822 are linked with a recombination frequency of 0.26. As a result of this research, we concluded that this marker can be used to select homozygous resistant sunflower plants for resistance to downy mildew in marker-assisted selection (MAS).