Flowering ecotypes of Capsella bursa-pastoris (L.) Medik. (Brassicaceae) analysed by a cosegregation of phenotypic characters (QTL) and molecular markers

Capsella bursa-pastoris (Brassicaceae) is an annual to biennial predominant ly autogamous species distributed worldwide. Using a linkage map with RAPDs and isozymes we studied quantitative trait loci (QTL) controlling phenotyp ic traits in this invasive species. To obtain a mapping population we cross ed two plants occurring in different climatic regions in California, USA (C entral Valley and Sierra Nevada) with the most diverse ecotypes (phenotypic parameters) and genotypes (isozyme multilocus genotypes). A hundred and th irteen F-2 individuals were raised and analysed for segregation at 107 RAPD s, six isozyme loci, and one locus determining leaf type. The number, locat ion and magnitude of genes underlying 13 traits were determined by using bo th interval and composite interval mapping. Two to five QTL affecting one c haracter have been detected. Altogether the 13 quantitative traits produced 48 QTL. The inheritance patterns of trails ranged from those controlled by one QTL with a major effect to those controlled by several QTL with only m inor effects. Closely linked QTL, e.g. onset of flowering with rosette leaf number, were interpreted as pleiotropic. Three major QTL account for onset of flowering. These loci were linked to at least three isozyme loci and se veral other QTL responsible for developmental traits like rosette leaf numb er. Heritability of quantitative traits, segregation of the leaf type, and segregation of the allozymes was tested in the F-3 generation. We conclude that historical events alone are insufficient to explain the distribution p attern of isozyme multilocus genotypes during the colonization of new regio ns and habitats. The present evidence indicates that ecotypic adaptation an d genetic linkage of isozyme loci with adaptive characters are involved. (C ) 2000 Annals of Botany Company.