Different cultivars of in vitro plants of potato Solanum tuberosum L. were cultivated with a bacterium Clavibacter michiganensis ssp. sepedonicus (Spieck. et Kott.) Skaptason et Burkh., causing wilt of the overground part and ring rot of tubers. Development of disease symptoms (chlorosis, growth suppression) closely correlated with strong acidification of the medium, caused by the bacterium producing extracellular polysaccharides. However, root cells of the host plant (potato) and other non‐host plants (seedlings of tomato, wheat and radish) were able to restore extracellular pH. The efficiency of such restoration correlated with the resistance of the potato cultivar to bacteriosis. Plasma membrane and vacuolar H+‐ATPases were not involved in the stabilization of extracellular pH‐homeostasis, but a significant role was played by the buffer capacity of the cells. The maintenance of pH‐homeostasis in the plants is inferred to be one of the main factors of nonspecific resistance.