Polyploid cytotypes and formation of unreduced male gametes in wild and cultivated fennel (Foeniculum vulgare Mill.)

Foeniculum vulgare Mill. (2n=22) is an herbaceous species native to the Mediterranean region and naturalized in many temperate areas around the world. It includes subsp. piperitum and subsp. vulgare which are, respectively, the wild and cultivated forms. Fennel is of economic importance both as a vegetable crop and for its wide use in the food and pharmaceutical industries. In recent years, the therapeutic and pharmacological potential of this species has been widely analyzed, its cytogenetic traits have aroused less interest. Therefore, the intention of this study was to reduce this gap by investigating some aspects, such as the variations in its chromosome number and the occurrence of polyploidization events, so far neglected. By means of extensive chromosome counting, the presence of tetraploid cytotypes has been discovered both in the wild and cultivated fennel. Moreover, the analysis of pollen and PMCs at the tetrad stage provided evidence for spontaneous sexual polyploidization as the most probable origin of the tetraploid cytotypes discovered. The results of this study provide the first evidence of the occurrence of polyploidization events in F. vulgare and suggest that the use of 2n gametes could be a useful approach to genetic improvement of this crop.