Effect of water on bacterial multiplication in plant tissue

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Abstract
When pathogenic and non-pathogenic bacteria were inoculated into bean leaves which were then kept saturated with water, those bacteria which are normally limited in growth increased in numbers. Pathogens in heterologous relationships with beans (Pseudomonas lachrymans and Ps. syringae) multiplied at a rate equal to the homologue Ps. phaseolicola, and to higher stationary-phase populations than developed under normal conditions of plant growth. Non-pathogenic bacteria (Ps. fluorescens, Ps. putida, and Erwinia herbicola) increased in numbers, but their stationary-phase populations were lower than those of the pathogens. Peptone added as a bacterial nutrient to the inoculum of Ps. fluorescens did not affect the growth of the non-pathogen in bean leaves. The availability of nutrients and water to bacteria in the intercellular spaces of leaf tissue may be important parameters regulating their development. The function of water as a determinant of specificity in host-pathogen relationships in the field is discussed.