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United States Department of Agriculture

Agricultural Research Service

Title: Genetic Mapping of Sulfur Assimilation Genes Reveals a QTL for Onion Bulb Pungency

Authors
item Mccallum, John - CROP&FOOD RS-NEW ZEALAND
item Pither-Joyce, Meeghan - CROP&FOOD RS-NEW ZEALAND
item Shaw, Martin - CROP&FOOD RS-NEW ZEALAND
item Kenel, Fernand - CROP&FOOD RS-NEW ZEALAND
item Davis, Sheree - CROP&FOOD RS-NEW ZEALAND
item Butler, Ruth - CROP&FOOD RS-NEW ZEALAND
item Scheffer, John - CROP&FOOD RS-NEW ZEALAND
item Jakse, Jernej - UNIV OF WI-MADISON
item Havey, Michael

Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 3, 2006
Publication Date: December 16, 2006
Citation: Mccallum, J., Pither-Joyce, M., Shaw, M., Kenel, F., Davis, S., Butler, R., Scheffer, J., Jakse, J., Havey, M.J. 2006. Genetic Mapping of Sulfur Assimilation Genes Reveals a QTL for Onion Bulb Pungency. Journal of Theoretical and Applied Genetics. 114:815.822.

Interpretive Summary: Onion exhibits wide genetic and environmental variation in bioactive organosulfur compounds that affect flavor (pungency) and health benefits. A genetic map that included candidate genes for sulfur assimilation was used to identify genomic regions affecting pungency in the cross 'W202A' x 'Texas Grano 438'. Linkage mapping revealed that genes encoding plastidic ferredoxin-sulfite reductase (SiR) and plastidic ATP sulfurylase (ATPS) are closely linked (1-2cM) on chromosome 3 of onion. Inbred families used to construct the genetic map were grown in replicated trials in two environments and bulb pungency was evaluated as pyruvic acid or lachrymatory (tearing) factor. Broad-sense heritability of pungency was estimated to be 0.78-0.80. QTL analysis revealed significant associations of both bulb pungency and soluble solids content with marker intervals on chromosomes 3 and 5, which have previously been reported to affect bulb carbohydrate composition. Highly significant associations were observed between ATPS and SiR and bulb pungency, but not with bulb solids content. Genetic models suggest that the region carrying these candidate genes controls 30-50% of genetic variation for pungency. Therefore, these markers may provide a practical means to select for lower pungency without correlated selection for lower solids. This research is of interest to plant scientists and breeders interested in developing health-enhancing onions with lower pungency.

Technical Abstract: Onion exhibits wide genetic and environmental variation in bioactive organosulfur compounds that impart pungency and health benefits. A PCR-based molecular marker map that included candidate genes for sulfur assimilation was used to identify genomic regions affecting pungency in the cross 'W202A' x 'Texas Grano 438'. Linkage mapping revealed that genes encoding plastidic ferredoxin-sulfite reductase (SiR) and plastidic ATP sulfurylase (ATPS) are closely linked (1-2cM) on chromosome 3. Inbred F3 families derived from the F2 population used to construct the genetic map were grown in replicated trials in two environments and bulb pungency was evaluated as pyruvic acid or lachrymatory factor. Broad-sense heritability of pungency was estimated to be 0.78-0.80. QTL analysis revealed significant associations of both pungency and bulb soluble solids content with marker intervals on chromosomes 3 and 5, which have previously been reported to condition pleiotropic effects on bulb carbohydrate composition. Highly significant associations (LOD 3.7-8.7) were observed between ATPS and SiR Loci and bulb pungency but not with bulb solids content. This association was confirmed in two larger, independently derived F2 families from the same cross. Single-locus models suggested that the partially dominant locus associated with these candidate genes controls 30-50% of genetic variation in pungency in these pedigree. These markers may provide a practical means to select for lower pungency without correlated selection for lowered solids.

Last Modified: 12/22/2014
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