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University of Windsor (1996)

Reproductive biology of the perennial desert shrub, Thymelaea hirsuta, studies in gender, self-fertility and architecture

Morbia Rita

Titre : Reproductive biology of the perennial desert shrub, Thymelaea hirsuta, studies in gender, self-fertility and architecture

Auteur : Rita Morbia

Université de soutenance : University of Windsor (Canada)

Grade : Master of Science 1996

Résumé
The modular construction of plants allows them to display significant phenotypic plasticity in both morphology and sex expression. Thymelaea hirsuta (Thymelaeaceae) is a xerophytic evergreen shrub cornmon to the Mediterranean region and known to dernonstrate significant variability in sex expression. A series of observational and experimental studies were carried out to investigate the nature of this variability in greenhouse-raised plants. Seeds were obtained from Egyptian populations, and following seedling establishment, an irrigation treatment was applied. Plants were watered every 3 days, 6 days or 9 days. A survey of two year old flowering plants (n = 305) showed significant bimodality in sex expression. Quantitative gender estimates indicated that individual plants tended to be either more male or more female. Water treatment had no significant effect upon estirnates of gender, number of male flowers, number of fernale flowers, total number of flowers or an index of sexual lability. A controlled pollination study revealed significant differences in seed mass among geitonogarnous, half-sib and outcrossed treatments, resuking in an estimate of inbreeding depression (6) of 0.23. Nonsignificant differences in fruit set were also observed. In general, selfing resulted in less fit progeny. To examine the effect of water treatment on various morphological ("architectural") parameters, repeated measurements were taken every two months on a subset of 202 plants for a total of ten months. Water treatment, time and the interaction effect between water treatment and time al1 significantly affected plant architecture, particularly height. Male, fernale and hermaphrodite flowers were compared for differences in position. There were significant differences among male, female and hermaphrodite flowers with respect to plant height, vertical distribution and branch order, suggesting that male flowers and female flowers may have different morphological optima. These studies indicate that selection for the evolution of dioecy in Thymelaea hirsuta may involve a combination of selection for outcrossing and resource or pollinator efficiency.

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Page publiée le 29 mars 2010, mise à jour le 4 février 2018