potatoes are one of the most important crops in the world. For the protection of environmental and human health (by reducing pesticide inputs), to avoid problems associated with pesticide-resistant crop-plant pathogens and to safeguard global food security, there is a pressing need to develop novel, eco-friendly, and cost-effective control methods for pathogens. The potato-pathogens Phytophthora infestans (late-blight which infects the plant above-soil) and Fusarium species (which typically cause dry-rot of stored tubers) can cause loses of 100 and 25% respectively. The current study was carried out to explore fundamental aspects of microbial ecology that can inform biological strategies for the control of potato-pathogenic microbes. The Introduction (Chapter 1) discusses what is currently known about microbial interactions and solute activities of biologically relevant substances, and outlines current control methods for potato pathogens and current biological controls. Chapter 2 explores the hypothesis that some microbial species can dominate specific habitats, characterizes and defines open habitats of microbes, and determines the traits that can enable some species to dominate open habitats. Chapter 3 reports the development and validation of a new, spectrophotometric method for the quantification of the macromolecule-destabilising (chaotropic) or stabilising (kosmotropic) activities of diverse substances; the method was tested via application to the characterisation of a newly discovered, deep-sea brine lake - Lake Kryos - which has high concentrations of the chaotropic salt, magnesium chloride. Chapter 4 determines the implications of chaotropicity in two types of biotechnological process: product toxicity in biofuel fermentations and mode-of-action of antifungal compounds. Chapter 5 reports a sampling campaign to obtain ecophysiologically diverse potato-associated microbes, and the development of a protocol to quantify their inhibitory potency against potato-pathogenic microbes. Chapter 6 determines (both qualitatively and quantitatively) the nature of interactions between P. infestans or Fusarium species against and the potential biocontrol agents in relation to inhibitory potency and whether the latter can also promote the multiplication of potato pathogens.