Cultivated rice is a staple food crop grown worldwide. A major threat to the production and yield of cultivated rice is due to a closely related agricultural weed, weedy rice. Most weedy rice populations have evolved through the process of de-domestication of different cultivated rice varieties grown worldwide. During this process, these populations have gained competitive traits such as increased seed shattering ability. In this dissertation thesis, I sought to determine if there are potential physiological differences and genetic mechanisms responsible for the increased competitive ability of weedy rice in cultivated rice fields. In Chapter 1, I determined and compared the root endophytic microbial community composition, diversity, and richness of multiple genotypes of weedy and cultivated rice. I found no distinct differences between community composition, however, cultivated rice was found to have higher bacterial richness and diversity. In Chapter 2, I isolated the culturable seed endophytic microbiome of weedy and cultivated rice and assessed the isolates for four plant growth-promoting abilities: nitrogen fixation ability, indole-3-acetic acid production, phosphate solubilization, and iron scavenging ability. We found microbial isolates from these weedy or cultivated rice groups do not have distinctly different plant growth-promotion ability. The top performing microbial isolates were used as seed bioinoculants and we demonstrated a differential response in seedling growth between weedy and cultivated rice. In Chapter 3, I conducted a quantitative trait locus mapping study to identify potential genomic regions that are responsible for seed shattering in weedy rice. In this work, I identified a marker that was identified as a single nucleotide polymorphism previously suggested as influential on seed shattering in weedy rice. We found that this G to T mutation was correlated with a high shattering ability and a defined abscission zone in our mapping population and in created hybrid inbred families. Overall, these findings build upon our foundation of weedy rice competitive ability which is important for the creation of novel mitigation strategies.