ON THE BACTERIA RESPONSIBLE FOR SOFT ROT IN STORED POTATOES, AND THE REACTION OF THE TUBER TO INVASION BY BACTERIUM CAROTOVORUM (JONES) LEHMANN & NEUMANN

Bacterium carotovorum (Jones) Lehmann & Neumann and Pseudomonas syringae van Hall were the only two species of Gram-negative bacteria isolated from rotting potatoes collected from clamps in England in 1945-7. Both were found capable of producing a rot under known conditions, and both were isolated on plates of a pectate-gel medium which is liquefied by these bacteria. Ps. syringae has not been recorded before as causing a rot of stored potatoes. In a slightly different type of rot which was ropy or gassy and often pink in colour, Gram-positive spore-forming bacilli were found, generally associated with Bacterium carotovorum. These bacilli proved to be anaerobes–species of Clostridium –one of which, when inoculated together with Bacterium carotovorum, produced a gassy rot pink in colour.
On infection by Bad. carotovorum the tuber reacts to form a barrier of suberized cells, the extent and efficiency of which depend on temperature and relative humidity. Low temperatures and a low humidity favour the formation of the barrier and eventually of periderm; high temperatures favour the multiplication of the bacteria the advance of which is limited by humidities not reaching saturation. Fluctuations of temperature or humidity may promote a succession of barriers.