Hybridization experiments in the genus Luzula IV. Studies with taxa of the campestris-multiflora complex from the Nothern and Southern Hemispheres

Abstract

Material of the widely distributed campestris-multiflora complex of genus Luzula has been collected from different localities in its areas in Europe, North America, and Japan in the Northern Hemisphere, and in Australia and New Zealand in the Southern Hemisphere. Individuals from these localities have been crossed intra- and inter-regionally, in order to determine the differentiation between the studied populations as expressed in the intensity of crossing barriers. F1-hybrids have been obtained in all tried taxa combinations. The sterility of the hybrids is of the postzygotic type, showing up in F1 and/or F2. The sterility barriers as isolating mechanisms are enhanced, in certain individual combinations, by sub-lethality of F1 or by the occurrence of abnormal segregates in F2. The intensity of the crossing barriers, determined by the mean fertility reduction of the hybrid populations in first and second generations, is approximately proportional to the distance between the geographical origins of the parental populations. The intensity of the sterility barriers is, furthermore, dependent on the effect of the selection pressure brought about by environmental stress and varying with the ecology of the habitats of the crossed populations.