Undergraduate Honors Theses

Thesis Defended

Fall 2018

Document Type


Type of Thesis

Departmental Honors


Ecology and Evolutionary Biology

First Advisor

Dr. Stacey D. Smith

Second Advisor

Dr. Barbara Demmig-Adams

Third Advisor

Dr. Robert Wyrod


Although the overarching process of plant breeding biology has received considerable attention in the plant sciences, few studies thoroughly examine the complexities of breeding system variability. Physalis acutifolia is a self-incompatible (SI) flowering plant in the Solanaceae family native to the southwestern United States. Self-incompatibility (SI) is a reproductive adaptation that serves to promote outcrossing and increase genetic fitness, and it is the opposite of self-compatibility (SC), which permits self-fertilization. Occasionally, certain species will be capable of employing more than one reproductive strategy. In P. acutifolia, specimens were collected from a variety of locations in the southwest U.S., and SI and SC populations were identified through preliminary crossing experiments in a greenhouse. Using these data, I focused on pollination crosses of SI and SC populations of P. acutifolia with three other species in the Physalis genus. These designed crosses contained a variety of SI and SC populations, and were intended to test the SI x SC hypothesis, which states that species that are self-compatible are also more likely to be compatible with an SI species, but the converse would not be true. Based on this previous work, I hypothesized that a SC female (the flower being pollinated) would be successfully fertilized by an SI male (the pollen donor), but that the reciprocal would not be true. Flowers received one of four treatments: emasculated and not crossed (negative control); crossed with individuals from the same location (positive control); pollinated with self pollen (experimental treatment 1); and crossed with individuals of a different species (experimental treatment 2). There was a statistically significant difference between the crossing outcomes of SI and SC species (p-value: 0.00247). However, there is not sufficient evidence to suggest that P. acutifolia consistently behaves as predicted by the SI x SC hypothesis. This experiment addresses the complexities of breeding systems, and is a necessary first step for understanding how and why such complexities occur.