Complex sentence: Little to no genetic diversity makes crops extremely susceptible to widespread disease; bacteria morph and change constantly and when a disease-causing bacterium changes to attack a specific genetic variation, it can easily wipe out vast quantities of the species.
Split into simpler sentences: Little to no genetic diversity makes crops extremely susceptible to widespread disease. When a disease-causing bacterium changes to attack a specific genetic variation, it can easily wipe out vast quantities of the species.