M. Amoozadeh - Department of Plant Breeding and Biotechnology, Urmia University, P. O. Box ۱۶۵, km ۱۲ Nazlou Road, Urmia, Islamic Republic of Iran.
R. Darvishzadeh - Department of Plant Breeding and Biotechnology, Urmia University, P. O. Box ۱۶۵, km ۱۲ Nazlou Road, Urmia, Islamic Republic of Iran.
R. Davar - Institute of Biotechnology, Urmia University, Shahid Beheshti St., Urmia, Islamic Republic of Iran.
B. Abdollahi Mandoulakani - Department of Plant Breeding and Biotechnology, Urmia University, P. O. Box ۱۶۵, km ۱۲ Nazlou Road, Urmia, Islamic Republic of Iran.
P. Haddadi - INRA, Institute Jean-Pierre Bourgin (IJPB), ۷۸۰۲۶, Versailles Cedex, France.
A. Basirnia - Department of Plant Breeding and Biotechnology, Urmia University, P. O. Box ۱۶۵, km ۱۲ Nazlou Road, Urmia, Islamic Republic of Iran.

Basal stem rot caused by Sclerotinia sclerotiorum (Lib.) de Bary is one of the most important diseases of sunflower. Quantitative trait loci (QTL) implicated in partial resistance to two isolates of S. sclerotiorum (SSU۱۰۷ and SSKH۴۱) were investigated using F۹ recombinant inbred lines (RILs) from the cross between sunflower parental lines PAC۲ and RHA۲۶۶. Experiments were conducted in completely randomized design with ۳-۶ replications under controlled conditions. The reaction of genotypes to basal stem rot disease was evaluated by measuring the percentage of necrosis area three days after inoculation. Combined analysis of experiments showed significant interactions between sunflower genotypes and S. sclerotiorum isolates suggesting that partial resistance to S. sclerotiorum should be isolate-specific in sunflower. QTLs were mapped using an updated high-density SSR and SNP linkage map. The map consisted of ۲۱۰ SSRs and ۱۱ gene-derived markers placed in ۱۷ linkage groups (LGs). The total map length was ۱,۶۵۳.۱ cM with a mean density of ۱ marker per ۷.۴۴ cM. A total of ۱۴ QTLs were detected for partial resistance to two isolates. The phenotypic variance explained by QTLs (R۲) ranged from ۰.۱۰ to ۹.۸۵. The sign of additive gene effects showed that favorable alleles for partial resistance to isolates came from both parents. Six QTLs were common between two isolates on LGs ۱, ۸ and ۱۷, whereas the others were specific for each isolate. Co-localized QTLs on LG ۱ were linked to the glutathione S-transferase gene (GST). The co-localized QTLs for partial resistance to basal stem rot isolates could be good candidates for marker assisted selection (MAS).

Basal stem rot, Helianthus annuus L, isolate specificity, partial resistance, QTL mapping