Endomycorrhizal fungi play an important role in the survival of plants on poor soils. Planting seeds into lunar soil at a lunar colony will be a challenge for seeds of any plant. The seeds will need a special microbial "tool kit" that will help them germinate and the young seedlings establish themselves. In this study, seeds of the prickly pear cactus, Opuntia ficus-indica, were chosen to examine the presence of fungus spores in the soil, inside the seeds and after germination in the rhizosphere, roots and other tissues of the young seedlings. The nutrient poor lunar regolith simulant JSC-1A was used as autoclaved or untreated growth medium. The mycorrhizal fungus Trichoderma viride was predominantly identified on the roots of new seedlings. This fungus also demonstrated the strongest effect on the germination rate of the seeds in comparison with other fungi isolated from the rhizosphere of Opuntia plants. T. viride was not detected within seeds and also not within seedlings, besides the root tips, whereas an arbuscular mycorrhizal Glomus species was seed-borne and present throughout most of the seedling. A close association between T. viride and a Glomus species associated with O. ficus-indica is demonstrated through light microscopic and electron microscopic images of the outside and inside root tips of the seedlings.