Development of bacterial populations in vivo in relation to plant pathogenicity

Rates of multiplication and population levels at stationary phase were determined quantitatively for pathogenic pseudomonads and non‐pathogenic bacteria in leaves of Phaseolus vulgaris . Multiplication of the homologous pathogen Pseudomonas phaseolicola suggested that inhibitory factors did not regulate its behaviour. Heterologous pathogens multiplied at lower rates and to lower stationary phase population levels, and non‐pathogens remained in stasis or declined slowly. A stimulation of bacteria normally limited in growth occurred when they were coinoculated with multiplying bacteria. The intercellular environment of plant tissue favoured general bacterial growth after inoculation with a multiplying organism, and it is concluded that this effect is connected with increased host cell‐membrane permeability allowing leakage of cellular components which support bacterial growth.