Detecting hybridization in mixed populations ofRhinanthus minor andRhinanthus angustifolius

Rhinanthus minor andRhinanthus angustifolius are known to hybridize in mixed populations in nature. These hybridization events can have important evolutionary consequences. The development and use of species-specific RAPD and ISSR markers allowed the detection of hybrid individuals not always distinguishable with morphological characters. Two mixed populations of different ages were studied. In a young mixed 2-year-old population, both individuals of the two parental species and F₁ hybrids were found using genetic analysis, showing that hybridization occurred rapidly. Flower morphology of F₁ hybrids was too variable to distinguish all these hybrids from the parental species. This morphological variability of F₁ hybrids was also confirmed in artificial crosses in the greenhouse. In an old and no longer mixed 30-year-old population, onlyR. angustifolius plants and a few genetically introgressed individuals close toR. angustifolius were present. Genetic markers showed traces of past hybridization and introgression. Unidirectional introgression ofR. minor intoR. angustifolius with the complete disappearance ofR. minor from this population was observed.