A Physiological and Molecular Analysis of the GenusNicotiana

Abstract An analysis of the evolution of the genusNicotianawas carried out with physiological and molecular tools. The capacity of explants from seedlings of several species ofNicotianato differentiate roots or shoots or to habituate was used to ascertain whether thein vitrobehavior of species has a nonrandom distribution in the genus. The results obtained allowed us to identify two groups of species, one root-forming prone composed ofPaniculatae(subgenusRustica) and the other composed ofAlatae, Repandae,andNoctiflorae(subgenusPetunioides), with a major tendency toward the production of shoots. Habituation capacity was characteristic of species randomly distributed throughout the phylogenetic tree. These data suggest fixation throughout the evolution of coadapted gene complexes (hormone-related genes) involved in the control of developmental processes. RAPDs, on the other hand, used as molecular markers for the clustering of related species, seem entirely coherent both with classical morphological and karyological studies and within vitrophysiological methods, supporting an early subdivision of the whole genus into two diverging developmental patterns.