Document Type

Thesis

Degree

Master of Science

Major

Biology, Plant Systematics

Date of Defense

12-4-2023

Graduate Advisor

Nathan Muchhala, PhD

Committee

Sara Miller, PhD

Aimee Dunlap, PhD

Behtany Zolman, PhD

Abstract

The human population is projected to continue growing throughout the remainder of the 21st century. Thus, agricultural production will need to increase drastically in order to ensure global food security. Management strategies aimed at enhancing crop pollination by promoting pollinator diversity have shown potential as an environmentally sustainable method of increasing yields. Optimizing the design and implementation of these strategies will require us to expand our understanding of the processes which influence crop pollen limitation. In this study, we examined pollen limitation in self-incompatible apple trees (Malus domestica) within urban orchards located in St. Louis, MO. In our first field season, we conducted a series of pollen limitation experiments to determine if the apple trees were pollen limited, as well as if the spatial arrangement of the trees or the receipt of heterospecific pollen affected pollination success. In our second field season we conducted an experiment which aimed to determine if different bee taxa (A. mellifera, O. cornifrons, and Andrena sp.) differed in their rates of outcross pollen transfer. We found that the apple trees were experiencing pollen limitation, and that this was likely due to high rates of geitonogamous pollen deposition. We also found evidence which indicated that honeybees (A. mellifera) moved between the apple trees less often than the other bee taxa, leading to high levels of within-plant pollen transfer and low rates of outcross pollen deposition. Key words: Malus, pollen limitation, ecological intensification, urban agriculture, pollinators

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