ABSTRACT
It has long been recognized that the monoculture of what leads to the development of soils that are suppressive to take-all, a disease of wheat caused by Gaeumannomyces graminis var. tritici. This suppressiveness is due to the development of populations of microbes, especially fluorescent pseudomonads, in the soil that are inhibitory to the growth of pathogens. It is known that different biological mechanisms account for this phenomenon, known as biocontrol. In many cases, biocontrol activity from a single microbe is derived from a combination of these mechanisms. This chapter focuses primarily on the role of antifungal compounds which are increasingly believed to be the dominant factor determining biocontrol activity in many systems. Antibiotic metabolites for which important roles in biocontrol have clearly been demonstrated include phenazine-1-carboxylate and 2, 4-diacetylphloroglucinol. In addition to controlling soil-borne fungal pathogens, recent reports have demonstrated that some rhizosphere bacteria are able to induce resistance to invasion by foliar plant pathogens.
