The answer is; a loss in biodiversity due to the replanting of the same modified crops each year
Monoculture has a drastic effect on biodiversity. Monoculture reduces the genetic diversity in a region and hence the environment is unable to maintain itself. This makes the environment less adaptable to environmental changes since natural selection acts on genetic diversity. Biodiversity is also important for living communities because it provides critical ecosystem services and resources critical for life, such as nutrient cycling.