PCR-based markers facilitating marker assisted selection in sunflower for resistance to downy mildew

Sunflower (Helianthus annuus L.) production is endangered by several diseases, necessitating sophisticated disease management strategies. Downy mildew of sunflower, incited by Plasmopara halstedii (Farl.) Berl. et de Toni, is a major sunflower disease. Recent reports of pathotypes resistant to metalaxyl [N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-DL-alanine methyl ester], which was used as a seed treatment against downy mildew, showed the necessity to breed for durable downy mildew resistance in future hybrids. This process can be accelerated by marker assisted selection (MAS) including pyramiding of several resistance genes. The objective of this study was to develop molecular markers for the Pl(2) gene of cultivated sunflower, which confers resistance to downy mildew races 1, 2, 7, and 9. Two sets of near isogenic lines (AS110/AS110Pl(2) and S1358/S1358Pl(2)) and bulks of a segregating F-2 population were used to identify random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) markers. Public maintainer and restorer lines were used to evaluate the markers. Disease resistance was evaluated by the whole seedling immersion method. DNA was extracted from leaves at flowering. RAPD markers OPAA14(750) and OPAC20(831), as well as the AFLP marker E35M48-3, showed a tight linkage of about 2 centimorgans (cM) to the Pl(2) locus. RAPD marker OPAA11(1008) linked to a distance of about 6 cM with the resistance locus and could be converted to a SCAR marker. Closely linked RAPDs and the sequence characterized amplified region (SCAR) marker demonstrated their practicability for marker assisted breeding by differentiating between resistant and susceptible germplasm of a set of diverse sunflower inbred lines.