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ARS Home » Plains Area » Fargo, North Dakota » Edward T. Schafer Agricultural Research Center » Sunflower and Plant Biology Research » Research » Publications at this Location » Publication #311422
Title: Pl17 is a novel gene independent of known downy mildew resistance genes in the cultivated sunflower (Helianthus annuus L.)

Author
item Qi, Lili
item LONG, YUNMING - North Dakota State University
item Jan, Chao-Chien
item MA, GUOJIA - North Dakota State University
item GULYA, THOMAS - Retired ARS Employee

Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2014
Publication Date: 4/1/2015
Citation: Qi, L.L., Long, Y.M., Jan, C.C., Ma, G., Gulya, T.J. 2015. Pl17 is a novel gene independent of known downy mildew resistance genes in the cultivated sunflower (Helianthus annuus L.). Journal of Theoretical and Applied Genetics. 128(4):757-767. DOI:10.1007/s00122-015-2470-8.

Interpretive Summary: Sunflower downy mildew (DM) is a widespread disease with regular occurrence in the United States and worldwide. The disease can cause heavy yield losses of 50 to 95 percent in cool, wet years and adversely affects other aspects of seed quality. Because of this destructive potential, DM is one of the most serious sunflower diseases. The use of resistant hybrids, where available, is the most efficient measure of controlling downy mildew. DM resistance in the USDA inbred line, HA 458, has been shown to be effective against all virulent races of P. halstedii currently identified in the United States. To determine the chromosomal location of this resistance, 186 F3 families derived from a cross of HA 458 with HA 234 were tested for their resistance to DM race 734. The segregation ratio of the population supported that the resistance was controlled by a single dominant gene, Pl17. Simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) primers were used to identify molecular markers linked to Pl17. Bulked segregant analysis using 849 SSR markers located Pl17 to linkage group (LG) 4, which is the first DM gene discovered in this linkage group. An F2 population of 186 individuals was screened with polymorphic SSR and SNP primers from LG4. Two flanking markers, SNP SFW04052 and SSR ORS963, delineated Pl17 in an interval of 3.0 cM. The markers linked to Pl17 were validated in a BC3 population. A search for the physical location of flanking markers in sunflower genome sequences revealed that the Pl17 region has a recombination frequency of 0.59 Mb/cM, which is a 4-fold higher recombination rate relative to the genomic average. This region can be considered amenable to molecular manipulation for further map-based cloning of Pl17.

Technical Abstract: Downy mildew (DM), caused by Plasmopara halstedii (Farl.) Berl. et de Toni, is one of the serious sunflower diseases in the world due to its high virulence and the variability of the pathogen. DM resistance in the USDA inbred line, HA 458, has been shown to be effective against all virulent races of P. halstedii currently identified in the United States. To determine the chromosomal location of this resistance, 186 F2:3 families derived from a cross of HA 458 with HA 234 were phenotyped for their resistance to race 734 of P. halstedii. The segregation ratio of the population supported that the resistance was controlled by a single dominant gene, Pl17. Simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) primers were used to identify molecular markers linked to Pl17. Bulked segregant analysis using 849 SSR markers located Pl17 to linkage group (LG) 4, which is the first DM gene discovered in this linkage group. An F2 population of 186 individuals was screened with polymorphic SSR and SNP primers from LG4. Two flanking markers, SNP SFW04052 and SSR ORS963, delineated Pl17 in an interval of 3.0 cM. The markers linked to Pl17 were validated in a BC3 population. A search for the physical location of flanking markers in sunflower genome sequences revealed that the Pl17 region has a recombination frequency of 0.59 Mb/cM, which is a 4-fold higher recombination rate relative to the genomic average. This region can be considered amenable to molecular manipulation for further map-based cloning of Pl17.