Osservazioni sul comportamento sessuale delPopulus tremulaL. in Italia

Abstract

OBSERVATIONS ON SEXUAL BEHAVIOUR OF POPULUS TREMULA L. IN ITALY. — A research has been carried on sex distribution of Populus tremula in Italy. On 101 observed populations the sexual ratio resulted of 2:1 in favour of male sex. The analysis of results referred to the two geographycal sectors of the peninsula, North and MiddleSouth, is however showing some discordant data in the sexual composition of several populations. In North-Italy the ratio results of 2,5:1 in favour of male sex, in MiddleSouth 1:1. These discordant results would show that male sex can be adapted whether in continental or in mountain climate. The Author deems that the geographycal position of populations and corresponding climatic characteristics can be responsible for the sexual selection, so that the several deviations wich are found in natural populations of P. tremula can get an explanation in an possible correlation between habitat and sex. The Author dwells particulary upon population discovered at Campiglione, near Pozzuoli (Naples). Stamens, varying in number from 2 to 4, were observed on almost all the pistillate flowers of every single catkin of these individuals and especially from the base to a little over halfway up the catkin. The high proportion of bisexual catkins found on every individual examined leads to the conclusion that P. tremula is « polygamo-dioecious » in character, that is, it produces bisexual and unisexual character in the case of P. tremuloides, where, however, in the majority of the bisexual individuals, the percentage of hermaphrodite flowers on one catkin was very small (1–2%). These cases of bisexuality lead one to thing that dioecism is an acquired character in the genus Populus. This condition (wich, at least in the case of P. tremula, is perhaps to be connected with the poor fertility of the species) could in time have lead to the present geographycal distribution in colonies of isolated and sexually anbalanced individuals. These cold have survived to our times due to their aptitude vegetative propagation by means of suckers, giving rise to scattered clumps of unisexual individuals of the same clone. The finding of these bisexual individuals is of considerable importance for applied genetics, and could initiate new researches in Italy to obtain genotypic and polyploid descendants.