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.