THE COLIFORM BACTERIA ASSOCIATED WITH POTATO BLACK-LEG AND OTHER SOFT ROTS I. THEIR PATHOGENICITY IN RELATION TO TEMPERATURE

Twelve glasshouse trials using twenty- five isolates of coliform soft- rot bacteria obtained from various countries showed that all the isolates produced typical black- leg of potato at temperatures of 76 degrees F. (24 center dot 5 degrees C.) or over, while some of them could also produce the disease at temperatures below 66 degrees F. (19 degrees C.). Thus the isolates fall into two main groups of which the high- temperature group originates mostly from tropical or subtropical countries or from plants grown in heated glasshouses, whereas the low- temperature group is indigenous in the north temperate regions. The high- temperature group comprises Pectobacterium carotovorum (Erwinia carotovora), P. carotovorum var. chrysanthemi (E. chrysanthemi) and P. carotovorum var. aroideae (E. aroideae). The low- temperature group consists of one variety, P. carotovorum var. atrosepticum (E. atroseptica). This temperature relation provides a possible means of discovering the origin of the black- leg pathogen in crops grown from Scottish seed in certain tropical or subtropical countries. As a result of this investigation it is considered that all soft-rot coliform bacteria are varieties of a single species, P. carotovorum (Jones) Waldee.