Patterns of molecular genetic variation in Plantago major and P. intermedia in relation to ozone resistance

Patterns of molecular genetic variation were examined in seed collections of Plantago major and Plantago intermedia , used previously to investigate the variations in ozone (O₃) resistance of these species across Europe. Total genomic DNA was amplified with random primers (random amplied polymorphic DNA (RAPD) and inter- single sequence repeats (SSR)) to produce 73 genetic markers. In addition, allozyme and chloroplast variations were surveyed. Genetic markers were examined for association with O₃ resistance in 18 British populations of P. major as well as 27 continental European populations of P. major and P. intermedia . Two populations that exhibited increased resistance to O₃ following several years' exposure to high O₃ concentrations in the field showed decreased genetic variation over time. In addition, their genetic composition showed no drastic change, which suggests that the change in resistance to O₃ was probably the result of selection on genotypes already present in local populations (selection in situ ). It appears that selection for O₃ resistance may occur in independent populations, and also may involve a number of genetically determined traits. Consequently the finding that plants with similar degrees of O₃ resistance are not closely related was not unexpected. However, the finding of an association of several genetic markers with O₃ resistance merits further investigation.