Sunflower Genetics and Genomics: From a Combined Linkage and Association Mapping of Flowering Time to the Development of a Transcriptome Web Portal

Association mapping and linkage mapping were used to identify quantitative trait loci (QTL) and/or causative mutations involved in the control of flowering time in cultivated sunflower Helianthus annuus. A panel of 384 inbred lines was phenotyped on testcrosses with two tester inbred lines across 15 location * year * environment combinations. A Recombinant Inbred Line (RIL) population was phenotyped both per se and on testcrosses giving 23 year *environment combinations.

In the association mapping approach, kinship estimation using 5923 single nucleotide polymorphisms (SNP) was found to be the best covariate to correct for effects of panel structure. Linkage disequilibrium decay ranged from 0.08 to 0.26 cM for a threshold of 0.20, after correcting for structure effects, depending on the linkage group (LG) and the ancestry of inbred lines. A possible hitchhiking effect is hypothesized for LG10 and LG8. A total of 11 regions across 10 LGs were found to be associated with flowering traits, and QTLs were mapped on 11 LGs in the 273 RILs population. Whereas eight regions were demonstrated to be common between the two approaches, the linkage disequilibrium approach did not detect a documented QTL that was confirmed using the linkage mapping approach.

Functional annotation of the genes holding the markers associated to flowering time through linkage desiquilibrium revealed the possible involvement of several flowering time controling pathways. This will be the opportunity to present a new web portal with functional annotation of sunflower transcripts publically available at www.heliagene.org