Although compatible phytopathogenic bacteria share a common ability to spread and multiply within the host plant, the manner in which they do this and the effect they have on the host plant (disease) vary considerably. This chapter considers general aspects of disease induction, different types of disease that are caused by plant pathogenic bacteria and the range of bacterial characteristics that are important in disease development.

The induction of bacterial disease

The ability of plant pathogenic bacteria to cause disease in a particular host plant depends on many features, including environmental aspects, plant physiology and development, and the expression of pathogenicity and virulence factors by the bacterial cells.

Environmental and physiological factors affecting disease development

Environmental factors are important in the development of plant disease for their direct effects on infection (Chapter 5) and for their indirect effects in determining the physiological status of the plant.

The various aspects of the plant which affect disease development are discussed by Lozano & Zeigler (1990) and include nutritional status, photoperiodic conditioning and stage of maturity and development.

Levels of macronutrients have been shown to be important in plant susceptibility to Erwinia stewartii, where elevated levels of N and P increase susceptibility and high levels of Ca and K increase resistance.