RAPD ANALYSES IN COLONIAL AND ANCESTRAL POPULATIONS OF CAPSELLA-BURSA-PASTORIS (L) MED (BRASSICACEAE)

Capsella bursa-pastoris is a neophyte in the New World. It arrived in California not before 200 years ago. Thirteen populations from Califor nia, seven from Spain and one from Germany were analyzed with RAPDs in order to trace the introduction history and to study the structure of the colonial populations. The results not only supported earlier hypo theses on the colonization of Capsella which were based in isozyme stu dies (Hurka, 1993; Hurka ef al, 1989) and phenotypic traits (Hurka and Neuffer, 1991), but helped also to understand the colonization histor y in more detail. Overall similarity in RAPD markers was greater betwe en Californian Central Valley and Spanish populations than it was betw een Central Valley and Californian mountain populations. It is conclud ed that genotypes preadapted to Mediterranean climate conditions were brought to California by Spaniards from Mexico. Their ancestral popula tions might be found in Spain which is strongly argued far by RAPD mar kers. They now occupy the Central Valley of California. The California n mountains are colonized by other genotypes, the source of which is n ot yet clear, but unlikely to be of Mediterranean climate origin. In g eneral, colonial Californian populations are genetically less variable than the European populations, but more variable than one would concl ude by isozyme studies. Population structures of the colonial populati ons as revealed by RAPD studies are in full accordance with the expect ed organization of genetic variability within and between populations of a predominantly self colonizing plant. Copyright (C) 1996 Elsevier Science Ltd