Reproductive behavior of the wild carrots Daucus pusillus and Daucus montanus from Argentina

Diploid Daucus pusillus Michx. (x = 11) and hexaploid Daucus montanus Humb. et Bonpl. ex Schult. (x = 11) are wild taxonomic carrot species, closely related to diploid Daucus carota L. (x = 9), spontaneous in Argentina. For efficient ex situ conservation and potential use in breeding, we investigated their reproductive behavior by (i) carrying out controlled pollinations among D. pusillus accessions from a wide distribution area in the country and between these and one plant of D. montanus that overlapped in flowering, and (ii) bagging a few inflorescences to prevent outcrossings. Part of the pollinated pistils were analyzed by fluorescence microscopy; others were left on the plant. Pollen viability was high (>87%) in all accessions, but heterogeneity for size and shape was observed. Seed formation in bagged inflorescences confirmed that D. pusillus is autogamous and revealed that D. montanus is self-compatible. Fully developed mericarps were obtained only in intraspecific combinations. It is concluded that populations classified as the taxonomic species D. pusillus constitute a biological species as well, and that they are closely related to the taxonomic species D. montanus because they share the basic chromosome number and are reproductively isolated mainly by post-zygotic barriers, which could be eventually circumvented via 2n gametes. Key words: hybridization, breeding barriers, taxonomic species, biological species. Resume: Daucus pusillus Michx. (x = 11) diploide et Daucus montanus Humb. et Bonpl. ex Schult. (x = 11) hexaploide sont des especes taxonomiques de carottes sauvages, etroitement reliees a Daucus carota L. (x = 9) diploide, spontanee en Argentine. Les auteurs ont examine leurs comportement reproducteur a des fins de conservation efficiente ex situ et d'utilisation potentielle en reproduction, (i) en realisant des pollinisations controlees parmi des accessions de D. pusillus provenant d'une large zone de distribution dans le pays, et entre elles et un plant de D. montanus dont les floraisons se chevauchaient, et (ii) en enveloppant quelques inflorescences afin de prevenir les croisements heterogenes. Une partie des pistils pollinises ont ete analyses par microscopie en fluorescence, les autres etant laisses sur la plante. La viabilite du pollen etait elevee (>87 %) chez toutes les accessions, mais une heterogeneite sur le plan de la taille et de la forme a ete observee. La grenaison des inflorescences enveloppees a confirme que D. pusillus est autogame et revele que D. montanus est auto-compatible. Des mericarpes pleinement developpes ont ete obtenus uniquement lors de combinaisons intraspecifiques. Les auteurs concluent que les populations attribuees a l'espece taxonomique D. pusillus constituent une egalement une espece biologique, et qu'elles sont etroitement reliees a l'espece taxonomique D. montanus car elles partagent le nombre de base de chromosomes et sont isolees sur le plan reproducteur principalement par des barrieres post-zygotiques, qui pourraient eventuellement etre contournees via un nombre diploide de gametes. [Traduit par la Redaction] Mots-cles: hybridation, barrieres reproductrices, espece taxonomique, espece biologique.
Introduction Three to four wild Daucus species (according to different authors), closely related to the edible carrot (D. carota L.), have been reported in Argentina: naturalized Daucus carota L., Daucus [...]