Estimating genetic variability in horticultural crop species at different stages of domestication

Domestication may be viewed as an evolutionary process, involving mechanisms like muta- tion, selection, genetic drift, hybridization and polyploidization, and in the end resulting in individuals with traits profitable for man. The advent of modern plant breeding has acceler- ated the domestication of plants considerably. Plant breeding is essentially a selection of plant material based on the existence of genetic variation. Genetic variation within species has been assessed by many methods and from several perspectives. In the present thesis, I study some genetical aspects in five crop species at different stages of domestication, using RAPD and morphological characters. The very first step in the domestication process in- volves selection of plant material in nature. Often, only a small amount of the variation present in the source material is represented in the samples taken. Domesticated populations of Turk‘s-cap lily proved, however, to contain as high levels of genetic variation as native populations. A totally different pattern was found in black chokeberry, as no variation at all could be found in cultivated material. In such a case, it is of vital importance to broaden the genetic basis within the crop, and this may be accomplished by incorporation of new selec- tions from nature. In order to optimize collection strategies, information must be aquired about genetic structure in these populations. Native plant material of black chokeberry turned out to contain substantial amounts of variation, however tetraploid and presumably apomic- tic plants produced progeny groups with much less variability than progeny groups derived from diploid plants. In native populations of lingonberry, individual clones extended at least 30m, which gives an indication of how to collect plants for maximizing the genetic variation within the material. In crops where valuable cultivars already have been developed, tools for simple and fast identification of these cultivars are needed. In the present thesis, both RAPD markers and morphology were successfully used to identify twelve cultivars of rhubarb. Moreover, to facilitate the breeding work, molecular markers linked to traits of interest are highly desirable. In this thesis, RAPD was used to search for a marker linked to sex determi- nation in sea bucktho