Environmental effects on pollen performance:potential consequences on gene flow

This thesis illustrates the effects of environmental factors on pollen performance and its importance on gene flow. Pollen competitive ability between the wild and cultivated species of four genera belonging to Cucurbitaceae family was compared to evaluate the evolutionary potential for selection on pollen tube growth rate. A possibility of hybrids formation between these species was also determined through hand pollination. Effects of herbivory and nutrients on pollen performance and female selection were determined in Cucumis sativus and N. alata. In addition, a study on flower colour inheritance on Nicotiana alata was carried out with the aim of obtaining a possible genetic marker for future gene flow studies. Hybrids between wild and cultivated species were formed in some species of Cucurbitaceae indicating a higher possibility of gene flow. Differences in individual variations on pollen tube growth rate within and between species suggest that there is an evolutionary potential for selection on this trait. Herbivory and nutrient factors were found to have effects on pollen performance on Cucumis sativus and N. alata. The interaction of the two factors was also found to be significant. Nutrient was found to influence herbivory effect on pollen performance. Effects of genotype-by-environment interaction in cultivars of the studied species were observed. The study on the flower colour inheritance suggested that in some cultivars of N. alata, flower colour could be used as a morphological marker on gene flow studies. Because pollen performance influences gene flow, an understanding of the factors affecting pollen performance is fundamental when conducting risk assessment studies. Since plants function the same way whether they are the result of natural selection, human selection, or gene modified, findings from cultivated plants or wild relatives will aid in assessing the environmental effects of all future introductions of GM crops