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Accueil du site → Doctorat → Afrique du Sud → Voortplantingspatrone van Felicia muricata (Thunb.) Nees, ’n suksesvolle indringerspesie in die semi-ariede grasveld van Suid-Afrika

North-West University (1995)

Voortplantingspatrone van Felicia muricata (Thunb.) Nees, ’n suksesvolle indringerspesie in die semi-ariede grasveld van Suid-Afrika

Jordaan A

Titre : Voortplantingspatrone van Felicia muricata (Thunb.) Nees, ’n suksesvolle indringerspesie in die semi-ariede grasveld van Suid-Afrika

Auteur : Jordaan A

Université de soutenance : North-West University

Grade : Doctor of Philosophy (PhD) 1995

Résumé
Reproductive aspects of 5 different populations of Felicia muricata, a successful encroacher species in the semi-arid grasslands of South Africa were investigated.

Chromosomal studies were conducted to determine chromosome numbers and pairing relations of chromosomes during meiosis I. Interpopulational variation in achene characteristics was determined as an indication of morphological and possible genetic variability. Megasporogenesis, pollen viability, male sterility, apomixis, seed and fruit abortion, and the ontogeny of male and female gametophytes were also investigated.

Two populations consisted of diploid plants (2n=18) and 3 populations of tetraploid plants (2n=36). Diploids and tetraploids produce a relatively high percentage of viable pollen and they exhibit predominantly normal bivalent formation during meiosis I.

Considerable variation among achene traits of different populations was detected and considered as an indication of genotypic variation. As achene traits are often related to dispersal and therefore regarded as a fitness component, it was proposed that these traits are shaped in relation to the specific micro habitat into which propagules are deposited.

An investigation of megasporogenesis revealed that the position of the functional megaspore is often variable. This is related to gamete competition and associated heterozygosity, often advantageous to plants occupying unfavourable or variable habitats.

Abnormal microsporogenesis and male sterility were exhibited by plants in all the investigated populations. These abnormalities may influence reproductive output and population size. They were also considered as a possible indication of a prospective shift in breeding system and of the plasticity of the breeding system in relation to the variability or homogeneity of the habitat.

Seed and/or achene abortion occur in every population. Abortion is assumed to be selective and of importance for regulating offspring genotype and heterozygosity. Seed set was not correlated to ploidy level. Seed set percentages of tetraploids often exceeded those of diploids.

Normal developmental patterns of male and female gametophytes were compared to specific stages at which abnormalities manifest during male sterility and seed abortion.

Apomictic processes such as apospory were detected in the ovules of all the investigated plants. Although a considerable number of unreduced embryo sacs are produced, agamospermy was not detected. It was presumed that these unreduced embryo sacs may become fertilized and their importance for the maintenance of diploid-tetraploid-haploid cycles was discussed. These cycles were considered to be important for the colonization of variable habitats and for the expansion of the geographical ranges of the species when they contribute to gene exchange between different populations and plants with different ploidy levels.

All of the investigated aspects that are probably integrated into a strategy for the effective colonization of the large number of micro-habitats which characterize the semi-arid grassland region of South Africa were discussed. Some aspects such as gamete competition, as well as seed and fruit abortion were regarded to be of specific importance to the maintenance of fitness in the different populations

Présentation (NRF)

Page publiée le 11 juillet 2017