Arbuscular mycorrhizal fungi (AMF) colonizing corn (Zea mays) roots as viewed with a compound light microscope (400x). Roots were cleared with 10 percent KOH and stained with 0.05 percent trypan blue in lactoglycerol to visualize fungal structures. Arbuscules, which are thought to be the site of nutrient exchange between the fungus and plant host, can be seen as branching, tree-like structures within plant cells. Fungal hyphae are the thick, thread-like structures that connect to the arbuscules and extend into soil, increasing the surface area of roots, and often improving plant nutrient and water uptake. The article in the American Journal of Botany reports the results of a greenhouse study to evaluate AMF colonization in nine genetically modified Bacillus thuringiensis (Bt) maize lines differing in number and type of engineered traits, and in five corresponding near-isogenic parental base-hybrids. Insect-resistant maize is genetically modified to express insecticidal toxins derived from the spore-forming soil bacterium, B. thuringiensis, to protect plants against damage from agricultural pests such as the corn rootworm and the European corn borer. Although Bt maize is widely cultivated, few studies have examined the interaction of different lines of Bt maize with symbiotic arbuscular mycorrhizal fungi in the soil. The authors examined differential levels of AMF colonization in multiple lines of Bt and non-Bt maize grown under the same experimental conditions. Transgenic Bt maize plants had lower levels of AMF colonization in their roots than did the non-Bt parental base-hybrids. This work contributes to the growing body of knowledge on the unanticipated effects of Bt crop cultivation on non-target soil organisms.