soilborne rhizosphere - incompetent biocontrol agents can be converted into rhizosphere - competent agents by exposing them to a mutagenic agent and then screening the exposed rhizosphere - incompetent agent for a strain showing increased cellulase production . the increased cellulase production characteristic serves to convert the originally rhizosphere - incompetent agent into one which is rhizosphere - competent . seeds of plants to be protected against various diseases can then be treated with the rhizosphere - competent strain . the roots of the plant , as well as its original seed , are protected by biocontrol agents produced by the disclosed process .