Thus, the expectation is that
periodic application of copper or streptomycin based
bactericides on crops to control bacterial diseases
increases the selection pressure for the development
of epiphytic bacterial populations resistant to these
chemicals, elevating the risks for transfer of resistance
within the plant pathogenic bacterial population. Once
resistance is acquired by the plant pathogen targeted
by these chemicals, either by mutation or conjugation,
the frequency of the resistant strains in the pathogen
population will increase eventually, resulting in less
effective disease control (Stall and Thayer 1962)