Abstract

<p>Cannabis sativa L. has been domesticated for fibre, oilseed, and marijuana; it also occurs as ruderal plants. “Marijuana” refers to plants selected for high concentrations of the chemical tetrahydrocannabinol (THC), while “hemp” refers to plants low in concentration of THC and which are domesticated for either stem fibre or oilseed. In my first chapter I review the botany of cannabis, taxonomy and origins, ethnobotany, and crop ferality. In my second chapter, I performed a study where achenes (“seeds”) from herbarium collections representative of these classes of C. sativa were assessed for variation in morphological characters and pericarp resistance to fracture. Multivariate analysis of the data revealed significant divergence among the groups. In contrast to ruderal plants, domesticated plants (hemp or marijuana) possessed achenes that are significantly longer, heavier, covered with a less adherent perianth, and lacking a pronounced basal attenuation. These characteristics reflect traits that are advantageous in domesticated plants, and are consistent with the "domestication syndrome”. Marijuana achenes, in comparison with hemp achenes, are shorter and darker. Achenes of fibre cultivars are larger than the achenes of oilseed cultivars. Achenes of dioecious oilseed cultivars are larger than the achenes of monoecious oilseed cultivars. We propose several mechanisms by which this phenotypic divergence may have occurred, including potential differences in outcrossing rate and the evolution of life history strategies among C. sativa groups that deserve further exploration. While only one species of Cannabis merits recognition, we postulate these phenotypic differences in C. sativa are a result of domestication for different purposes. In my final chapter I discuss the limitations and future studies. This work contributes a more complete understanding of cannabis morphology to the greater body of literature on plant domestication.</p>

Highlights

  • 1.4 Domestication Syndrome: Consistent Differences Between Crops and Wild Relatives To maximize harvest of the stored food in seeds, humans have frequently altered the phenotype of the plants, especially the morphology and physiology of seeds

  • The most significant modern crops differ from their wild ancestors in propagule features, often exhibiting the well-known “domestication syndrome,” and this study demonstrated several of these trends, including loss of disarticulation, reduced hull, and larger size in the domesticate, as well as loss of camouflage

  • The achenes of monoecious oilseed cultivars proved to be smaller than those of dioecious cultivars, presumably because the former suffer from inbreeding depression. These trends are consistent with a crop in its early stages of domestication for quite different purposes

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Summary

CHAPTER 1: INTRODUCTION

Angiosperm) plants are generally dioecious (and rarely monoecious) and possesses unisexual flowers that are wind pollinated (Amaducci, Coluzzi, Zatta, & Venturi, 2008). Escaped populations of weedy crop-derived plants grow outside of cultivation in many parts of the world, commonly in disturbed soils near ditches and streams (Small, Pocock, & Cavers, 2003). Such ruderal plants have evolved adaptations to local environments For at least 6000 years, the plant has been grown in north temperate areas, primarily as a fibrous stem crop, to a much lesser degree for oilseed These two “industrial hemp” cultigens have very limited levels of the euphoriant chemical tetrahydrocannabinol (THC), but relatively high amounts of the non-euphoriant compound cannabidiol (CBD). The seeds represent only a small part of the phenotype of C. sativa, they are, critical to its survival, as well as providing an important economic product, and so merit special attention

Achene Anatomy
Domestication Syndrome
Crop Ferality
Thesis Objectives
CHAPTER 2: MATERIALS & METHODS
Herbarium Specimens The Herbarium of Agriculture and Agri-food Canada in
Specimens Examined
Seed Dimensions
Seed Mass The weight each seed was determined using a digital balance (Mettler
Pericarp shade
Resistance to Pericarp Fracturing
Statistical Analysis
Differences Between Domesticated (Hemp and Marijuana) and North-Temperate, Low-THC Ruderal Plants
Differences Between Hemp and Marijuana Genotypes
Differences Among Dioecious Fibre, Dioecious Oilseed, and Monecious Oilseed Genotypes
Fracture Resistance in Relation to Pericarp Thickness
CHAPTER 4: DISCUSSION & CONCLUSIONS
Cannabis Crop Seeds are Larger than Ruderal Seeds
Marijuana Seeds are Smaller and Lighter than Hemp
Fibre Hemp Seeds are Heavier than Oilseed Hemp Seeds
Dioecious Genotypes Produce Heavier Seeds than Monoecious Genotypes
Thick Pericarps Protect Achenes from Fracturing
Future Studies & Limitations
Conclusion Humans have domesticated
Programming code to import images to MATLAB and convert it into a matrix
Findings
Programming code to calculate greyscale of achenes
Full Text
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