GENETIC-BASIS OF ADAPTATION - FLOWERING TIME IN ARABIDOPSIS-THALIANA

We have mapped QTLs (quantitative trait loci) for an adaptive trait, f lowering time, in a selfing annual, Arabidopsis thaliana. To obtain a mapping population we made a cross between an early-summer, annual str ain, Li-5, and an individual from a late overwintering natural populat ion, Naantali. From the backcross to Li-5 298 progeny were grown, of w hich 93 of the most extreme individuals were genotyped. The data were analysed with both interval mapping and composite interval mapping met hods to reveal one major and six minor QTLs, with at least one QTL on each of the five chromosomes. The QTL on chromosome 4 was a major one with an effect of 17.3 days on flowering time and explaining 53.4% of the total variance. The others had effects of at most 6.5 days, and th ey accounted for only small portions of the variance. Epistasis was in dicated between one pair of the QTLs. The result of finding one major QTL and little epistasis agrees with previous studies on flowering tim e in Arabidopsis thaliana and other species. That several QTLs were fo und was expected considering the large number of possible candidate lo ci. In the light of the suggested genetic models of gene action at the candidate loci, epistasis was to be expected. The data showed that ma jor QTLs for adaptive traits can be detected in non-domesticated speci es.